The impact of pre-operative oral carbohydrate loading on peri-operative outcomes: A systematic review and meta-analysis of randomised controlled trials

ABSTRACT

Background and Aims

Pre-operative oral carbohydrate loading is widely adopted in enhanced recovery after surgery protocols, yet its clinical benefits remain uncertain. This review aimed to determine the effect of pre-operative oral carbohydrate loading on the incidence of post-operative nausea and vomiting (PONV) and other peri-operative outcomes in surgical patients.

Methods:

MEDLINE, EMBASE, and CENTRAL databases were systematically searched from database inception to 31 August 2025. Randomised controlled trials examining the effects of pre-operative oral carbohydrate loading with conventional fasting or placebo in adult patients were included.

Results:

Ninety-eight trials involving 9,824 patients were included. The main pooled analysis showed lower incidence of PONV with oral carbohydrate loading prior to surgery [risk ratio (RR) 0.74, 95% confidence interval (CI) 0.58–0.94, P = 0.02, trial sequential analysis = inconclusive]. Significant reductions were also found in the carbohydrate group for pre-operative hunger [mean difference (MD) -1.56, 95% CI -2.57 to -0.55, P = 0.003], thirst (MD -1.61, 95% CI -2.35 to -0.88, P < 0.001), post-operative glucose level (MD -3.45, 95% CI -6.64 to -0.25, P = 0.03), insulin resistance (MD -1.21, 95% CI -1.70 to -0.72, P < 0.001), post-operative pain (MD -0.43, 95% CI -0.71 to -0.15, P = 0.003), and length of stay (MD -0.40, 95% CI -0.59 to -0.21, P < 0.001).

Conclusion:

Pre-operative oral carbohydrate loading may reduce PONV. However, this benefit was not confirmed in the sensitivity analysis restricted to low-risk bias studies. It also reduces pre-operative hunger and thirst, post-operative pain, and the length of hospital stay, although the certainty of evidence for these outcomes is low. The absolute effect sizes for post-operative pain and length of stay were small and of uncertain clinical importance. These findings should be interpreted with caution due to substantial heterogeneity, publication bias, and lower certainty of evidence.

INTRODUCTION

Post-operative nausea and vomiting (PONV) remains one of the most common anaesthetic complications. It is associated with patient discomfort, delayed recovery, and prolonged hospital stay.[1] Surgical patients have traditionally been instructed to undergo overnight fasting to minimise the risk of pulmonary aspiration during anaesthesia, but overnight fasting also worsens thirst, hunger, and peri-operative metabolic stress. Surgical trauma also provokes a neuroendocrine stress response characterised by peripheral insulin resistance, transient hyperglycaemia, and post-operative catabolism.[2]

Pre-operative oral carbohydrate loading has been proposed to improve patient comfort pre-operatively and reduce the risk of PONV without increasing the risk of pulmonary aspiration. The idea of pre-operative oral carbohydrate loading up to 2 h before anaesthesia was also incorporated into several enhanced recovery after surgery (ERAS) pathways for selected elective surgical patients.[3,4,5] However, recent studies have reported conflicting findings.[6,7] Beyond PONV, the effects of pre-operative oral carbohydrate loading on peri-operative comfort, metabolic, safety, and recovery outcomes also remain incompletely defined. Although several systematic reviews on this topic have been published, most have restricted to specific surgical populations, pooled a comparatively small number of trials, or have not incorporated trial sequential analysis and formal Grading of Recommendations Assessment, Development and Evaluation (GRADE) certainty assessment. Therefore, an updated systematic review and meta-analysis such as the present meta-analysis that synthesised all relevant trials published up to August 2025, standardised outcome definitions, and assessed the certainty and robustness of the cumulative evidence was necessary.

The current review evaluated adult surgical patients who received pre-operative oral carbohydrate loading compared with placebo or conventional fasting. We hypothesised that pre-operative oral carbohydrate loading reduces the incidence of PONV in adult patients undergoing surgery. The primary objective of this review was to evaluate the impact of pre-operative oral carbohydrate loading in the reduction of PONV. The secondary objectives were to examine the impact of pre-operative oral carbohydrate loading on pre-operative hunger and thirst scores, post-operative pain scores, post-operative serum glucose level, insulin resistance, residual gastric volume, and length of hospital stay.

METHODS

The Cochrane Handbook for Systematic Reviews of Interventions was used in conducting this review.[8] Prior to the literature search, the review protocol was published in the International Prospective Register of Systematic Reviews (PROSPERO) on 3 May 2025 (CRD420251036146). A population-intervention- comparison-outcomes (PICO) approach was used to generate the research questions [Supplementary Table 1].

Supplementary Table 1.

Population-Intervention-Comparison-Outcomes (PICO) table

Population	Adult patients aged above 18 years undergoing surgery
Intervention	Pre-operative oral carbohydrate loading
Comparison	Conventional fasting or placebo drink
Outcome	Peri-operative outcomes (post-operative nausea and vomiting, pre-operative hunger and thirst, post-operative pain, residual gastric volume, glucose, insulin resistance, length of stay)

Databases of EMBASE, Ovid MEDLINE, and CENTRAL were systematically searched from their respective database inception dates to 31 August 2025 for randomised controlled trials (RCTs) comparing pre-operative oral carbohydrate loading with conventional fasting or placebo in adult patients undergoing surgery. The authors did not apply any restrictions on language or publication date. The search term and strategy were included [Supplementary Table 2]. Additional studies were hand-searched from the references of all included papers and relevant systematic reviews.

Supplementary Table 2 Search strategy

Supplementary Table 2a EMBASE (1947 - 31 August 2025)

1	preoperative.mp. or exp Preoperative Care/ or exp Preoperative Period/	739114
2	perioperative.mp. or exp Perioperative Medicine / or exp Perioperative Care/ or exp Perioperative Period/	1388676
3	carbohydrate loading.mp. or exp Diet, Carbohydrate Loading/	953
4	1 or 2	1611427
5	3 and 4	647
6	limit 5 to humans	634
7	limit 6 to “remove medline records”	305

Supplementary Table 2b.

Ovid MEDLINE (1947 – 31 August 2025)

1	preoperative.mp. or exp Preoperative Care/ or exp Preoperative Period/	388838
2	perioperative.mp. or exp Perioperative Medicine / or exp Perioperative Care/ or exp Perioperative Period/	368826
3	carbohydrate loading.mp. or exp Diet, Carbohydrate Loading/	712
4	1 or 2	629615
5	3 and 4	260
6	limit 5 to humans	210

Supplementary Table 2c.

CENTRAL (1947 - 31 August 2025)

1	preoperative OR preoperative care OR preoperative period	51513
2	perioperative OR perioperative medicine OR perioperative care OR perioperative period	30644
3	carbohydrate loading OR diet, carbohydrate loading	453
4	#1 OR #2	74692
5	#3 AND #4	266

Inclusion criteria included: (a) RCTs examining the effects of oral carbohydrate loading versus conventional fasting or placebo before surgery and (b) trials involving adult patients (≥18 years old).

Exclusion criteria were: (a) observational studies, case series, case reports, and trials published as abstracts; (b) trials examining intravenous carbohydrate loading and a combination of oral carbohydrate with other confounders (chewing gum, whey protein, antioxidant); and (c) trials with healthy volunteers.

The primary outcome was the incidence of PONV. Secondary outcomes included length of hospital stay, residual gastric volume, pre-operative hunger, pre-operative thirst, post-operative pain, glucose level, and insulin resistance. Subgroup analysis was also conducted for the carbohydrate group, comparing it with the conventional fasting group and the placebo group for the incidence of PONV.

Two authors (TC, EH) screened the title and abstract of each study independently. Discussion was made with the third author (KN) to resolve any discrepancy. Both authors (TC, EH) independently screened the full texts, and again, any conflict was resolved by the third author (KN). The final studies were included based on consensus among all three authors. A standardised data extraction form was used to extract data from all included studies. Both authors (TC, EH) independently used the Cochrane Risk of Bias Assessment tool to assess the risk of bias for included RCTs.[9] Disagreements were resolved via a discussion with the third author (KN). In the case of missing data, the corresponding author of the individual trial was contacted in an attempt to retrieve the data.

Review Manager version 5.4 was used for statistical analyses.[10] A two-tail P value < 0.05 was considered as statistically significant. Findings were reported as Mantel–Haenszel risk ratio (RR) and mean difference (MD) for binary and continuous outcomes, respectively. For patient-reported outcomes measured using different numerical scales including hunger, thirst, and pain scores, data were harmonised by converting eligible scores to a common 0–10 scale before pooling. Mean and standard deviations were also transformed using the same conversion factor. Due to variation of study population, types of surgery, and dosage of carbohydrate load, a random-effects model was used to pool estimates. Heterogeneity was assessed using I² statistic, with values of <40%, 40–60%, and >60% categorised as low, moderate, and substantial, respectively. Sensitivity analysis was conducted for the primary outcome based on low risk of bias studies to ensure robustness of the findings. A funnel plot was also created to assess potential publication bias for the primary outcome.

The GRADE assessment of evidence and summary of findings were independently performed by two authors (TC, EH) using GRADEpro/GDT software.[11] The certainty of evidence was assessed based on five criteria (risk of bias, inconsistency, indirectness, imprecision, and publication bias). Any discrepancy was resolved by the third author (KN). Trial sequential analysis was performed for the primary outcome to assess the statistical reliability of the cumulative evidence and the risk of random errors due to sparse data and repeated significance testing in the meta-analysis using the trial sequential analysis viewer version 0.9.5.5 Beta (Copenhagen Trial Unit, 2017).[12] The required information size was calculated with 5% risk of type 1 error, a power of 80%, and model variance-based heterogeneity correction.

RESULTS

The study selection process is summarised in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow chart [Figure 1]. After removing duplicates, 655 citations were screened, and 98 articles were included in the review; six of these were identified through citation searching. Details of excluded studies are provided in the supplementary material [Supplementary Table 3].

Figure 1.

Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) flow diagram

Supplementary Table 3.

List of excluded studies

No.	Author	Year	Journal	Country	Age	Population	Surgery	Reason for exclusion
1	Svanfeldt et al.	2007	British Journal of Surgery	Sweden	25 - 75 years old	15	Elective open colorectal resection	Different comparator: The study compared the difference in effect between high-dose carbohydrate versus low-dose carbohydrate instead of carbohydrate drink versus placebo or conventional fasting.
2	Awad et al.	2010	Annals of Surgery	United Kingdom	18 - 80 years old	40	Elective laparoscopic cholecystectomy	Different intervention: The study provided oral nutritional supplement (ONS) which contains glutamine and antioxidants.
3	Tudor-Drobjewski et al.	2018	British Journal or Anaesthesia	Austria	2 - 18 years old	120	Elective endoscopic examinations	Different population: The study targeted children aged 2-18years old. Moreover, the participants undergone elective endoscopic examinations, which are not considered surgery.
4	Öbrink et al.	2019	Annals of Medicine and Surgery	Sweden	18 - 75 years old	98	Elective laparoscopic cholecystectomy or elective gynaecologic laparoscopy in general anaesthesia	Different intervention: The study provided chewing gum along with carbohydrate drink.
5	Aleisa et al.	2020	Dermatologic Surgery	USA	Adult patients (age not specified)	100	Mohs micrographic surgery for nonmelanoma skin cancer	Different intervention: The study provided acetaminophen along with carbohydrate drink for intervention group.
6	Ho et al.	2020	Trials	Malaysia	>18 years old	110	Elective surgery for gynaecological cancer	Different intervention: The study used whey-protein-infused carbohydrate drink for intervention group.
7	Balabolu et al.	2023	World Journal of Surgery	India	18 - 65 years old	100	Day care laparoscopic cholecystectomy	Different intervention: The study provided chewing gum along with carbohydrate drink for intervention group.
8	Zulkifli et al.	2023	Scientific Reports	Malaysia	>18 years old	80	Elective gastroscopy	Different setting: The study recruited participants for elective gastroscopy, which is not considered a surgery.

The clinical characteristics of included studies are summarised [Supplementary Table 4]. Of the 98 included RCTs,[13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110] the majority were single-centred, and six were multi-centred.[13,17,27,28,61,64] In four trials that included both oral and intravenous groups,[25,27,53,83] only data from the oral group were analysed. Most studies used a 12.5% maltodextrin-based oral carbohydrate solution, typically administered as 400 mL (equivalent to 50g carbohydrate) 2–3 h before surgery, with many trials including an additional 800 mL dose the night before surgery.[13,14,15,16,17,18,19,20,23,28,30,31,35,37,39,40,42,43,45,46,48,51,52,53,54,57,60,61,68,72,73,74,76,78,93,97,102] The most frequently used formulation was Nutricia PreOp®, a standardised iso-osmolar drink providing 50 kcal/100 mL. However, there was considerable variability in both the timing (ranging from single morning doses to split regimens over 12–24 h) and the product composition, with alternatives such as Clearfast®, ShuNeng®, and Arginaid Water® also used. In overall risk of bias assessment, 41 trials were of low risk,[22,24,28,33,39,43,44,45,47,48,50,53,55,57,59,60,62,66,67,72,74,77,78,80,81,87,88,91,92,93,94,96,97,98,99,100,101,104,106,108,110] 42 trials had some concerns due to bias from the randomisation process, measurement of outcome, or selection of the reported result,[13,14,15,16,17,18,19,20,21,25,26,27,29,30,32,34,36,37,38,40,41,49,51,52,54,57,58,63,64,68,69,70,71,76,79,82,83,84,86,89,102,103] and 15 trials were of high risk [Supplementary Figure 1 ^{(4.4MB, tif)} ].[23,31,35,42,46,61,65,73,75,85,90,95,105,107,109] Risk-of-bias assessment showed three main issues: 32 studies raised concerns about selective reporting because no protocol or registry entry was available; 20 trials did not adequately describe the randomisation method, thereby introducing potential bias; and eight trials were at high risk for missing outcome data owing to substantial or unexplained loss to follow-up. The overview of data analysis of primary and secondary outcomes is provided [Table 1]. Summary of findings and certainty of evidence using GRADEpro/GDT is presented [Table 2]. PRISMA checklists are provided in the supplementary material [Supplementary Table 5 and Supplementary Table 6].

Supplementary Table 4.

Clinical characteristics of included studies

No	Author(s) / Year	Country	Sample Size	Age*, years	Type of surgery	Intervention (I)	Control (C)	Placebo (P)	Brand of CHO drink	Outcome Measure d
1	Hausel et al./2001[13]	Sweden	252	Cholecystectomy: I: 49(36,58) P: 52(34,58) C: 48(37,59) Colorectal: I: 56(50,67) P: 56(46,69) C: 52(34,66)	Abdominal	800mL 12.5% CHO drink evening before surgery + 400mL morning of surgery	fasting since midnight	800mL flavoured water evening before surgery + 400mL morning of surgery	Nutricia Preop®; Numico, Zoetermeer, the Netherlands	Hunger; thirst; other wellbeing/comfort symptoms; nausea; pain; glucose; insulin
2	Soop et al./2001[14]	Sweden	15	I: 66±3 P: 58±3	Orthopaedics	800mL 12.5% CHO drink evening before surgery + 400mL 2h before insertion of epidural catheter	-	800mL of sweetened water evening before surgery + 400mL 2h before insertion of epidural catheter	Nutricia Preop®; Numico, Zoetermeer, the Netherlands	Glucose; insulin; substrate oxidation; energy expenditure; urinary urea excretion
3	Henriksen et al./2003[15]	Denmark	48	I: 64[44-82] C: 64[52-81]	Abdominal	400mL 12.5% CHO drink evening before surgery + 400mL	fasting with clear fluid up to 3h before	-	Unspecified	Glucose; insulin; IGF-1; free fatty acids; glucagon; CRP; handgrip
						up to 3h before anaesthesia	anaesthesia			strength; pulmonary function; gastric residual volume; nutritional intake; mobility; wellbeing/comfort symptoms
4	Bisgaard et al./2004[16]	Denmark	94	I: 42[24-69] P: 44[18-65]	Abdominal	800mL 12.5% CHO drink evening before surgery + 400mL 2h before anaesthesia	-	800mL flavoured water evening before surgery + 400mL 2h before anaesthesia	Nutricia Preop®; Numico, Zoetermeer, the Netherlands	Wellbeing/comfort symptoms; fatigue; pain; postoperative nausea and vomiting; sleep quality; actigraphy/physica l activity
5	Hausel et al./2005[17]	Sweden	174	I: 48.3±14.6 P: 46.8±14.9 C: 48±14.9	Abdominal	800mL 12.5% CHO drink evening before surgery + 400mL 2h before anaesthesia	fasting since midnight	800mL flavoured water evening before surgery + 400mL 2h before anaesthesia	Nutricia Pre-op®, Nutricia, Zoetermeer, The Netherlands	Postoperative nausea and vomiting; pain; antiemetic use
6	Yuill et al./2005[18]	United Kingdom	72	I: 52.8±2.5 P: 52.1±2.4	Abdominal	800mL 12.6% CHO drink	-	800mL placebo drink	Unspecified	Nutritional status; body composition;
						evening before surgery + 400mL 2h before anaesthesia		evening before surgery + 400mL 2h before anaesthesia		glucose; insulin; length of stay; postoperative complications
7	Breuer et al./2006[19]	Germany	188	I: 64±9 P: 64±10 C: 64±10	Cardiac	800mL 12.5% CHO drink evening before surgery + 400mL 2h before anaesthesia	fasting since midnight	800mL placebo drink evening before surgery + 400mL 2h before anaesthesia	Unspecified	Insulin; wellbeing/comfort symptoms; residual gastric fluid volume; morbidity
8	Noblett et al./2006[20]	United Kingdom	35	I: 58{30-77} P: 59{32-71} C: 55{21-79}	Abdominal	800mL 12.5% CHO drink evening before surgery + 400mL 3h before surgery	fasting since midnight	800mL of water evening before surgery + 400mL 3h before surgery	Vitaflo limited UK	Length of stay; return of gastrointestinal function; handgrip strength
9	Rapp-Kesek et al./2007[21]	Sweden	18	I: 71(1) † C: 73(1) †	Cardiac	400ml 12.5% CHO drink evening before surgery + morning on the day of surgery	fasting since midnight	-	Nutricia Pre-op®, Nutricia, Zoetermeer, The Netherlands	Residual gastric volume; glucose; insulin; HbA1c; C-peptide; glucagon; cortisol; IGF-1; growth hormone; epinephrine;
										norepinephrine; chromogranin A; pancreatic polypeptide
10	Järvelä et al./2008[22]	Finland	101	I: 64±8.6 C: 66.8±11.4	Cardiac	400mL 12.5% CHO 2h before anaesthesia	standard preoperative fasting	-	Nutricia Pre-op®, Nutricia, Zoetermeer, The Netherlands	Insulin; glucose; HbA1c; residual gastric volume; postoperative nausea and vomiting; pain; haemodynamic parameters; length of stay
11	Yagci et al./2008[23]	Turkey	70	I: 49.59±15.2 C: 43.11±15.1	Mixed	800mL 12.5% CHO drink evening before surgery + 400mL 2h before induction	fasting since midnight	-	Nutricia Pre-op®, Nutricia, Zoetermeer, The Netherlands	Residual gastric volume; gastric pH; glucose; insulin
12	Faria et al./2009[24]	Brazil	23	I: 47[19-65] C: 48[29-65)	Abdominal	200mL 12.5% CHO drink 2h before surgery	fasting for 8h	-	Nidex, Nestle, Brazil	Glucose; insulin; β-hydroxybutyrate; pyruvate; lactate; triglycerides; urinary nitrogen; postoperative vomiting
13	Helminen et al./2009[25]	Finland	210	I: 60±15 C: 58±4	Mixed	400mL 12.5% CHO drink between 06:00 and 07:00 morning of surgery	fasting since midnight	-	Nutricia Pre-op; Numici, The Netherlands	Thirst; hunger; pain; glucose; insulin; other wellbeing/comfort symptoms
14	Lauwick et al./2009[26]	Belgium	208	I: 45±13 P: 46±12	Head and neck	400mL 12.5% CHO drink 2h before surgery	-	100mL of water 2h before surgery	Unspecified	Postoperative nausea and vomiting; pain; analgesic use; hunger; thirst; anxiety; fatigue; time to first intake
15	Kaska et al./2010[27]	Austria	221	60.4{35-75}	Abdominal	400mL 12.6% CHO drink evening before surgery + 400-mL 2h before surgery	fasting since midnight	-	Preop© Nutricia	Glucose; insulin; biochemical markers; cardiac function; psychosomatic symptoms; residual gastric volume; gastric pH; handgrip strength; length of stay; postoperative complications
16	Mathur et al./2010[28]	New Zealand	162	I: 60[27-80] P: 65[22-81]	Abdominal	800mL 12.5% CHO drink evening before surgery + 400mL 2h before anaesthesia	-	800mL flavoured water evening before surgery + 400mL 2h before anaesthesia	Nutricia Preop®; Numico, Zoetermeer, the Netherlands	Fatigue; length of stay; infections; glucose; insulin; cortisol; inflammatory markers; muscle function; total body protein; other wellbeing/comfort symptoms
17	Wang et al./2010[29]	China	52	I: median 66 (48- 74) P: 62(48-74) C: 63(37-74)	Abdominal	400mL 12.5% CHO drink 3h before anaesthesia	fasting since midnight	400mL flavoured water 3h before anaesthesia	Nutricia Preop®; Numico, Zoetermeer, the Netherlands	Glucose; insulin; hunger; thirst; other wellbeing/comfort symptoms; muscle insulin-signalling markers
18	Özdemir et al./2011[30]	Turkey	90	Group 1: I: 45.66±10.09 P: 51.53±7.20 C: 47.66±8.89 Group 2: I: 45.80±9.74 P: 48.06±6.81 C: 45.5±9.98	Abdominal	800mL 12.5% CHO drink evening before surgery + 400mL 2h before surgery	fasting since midnight	800mL water evening before surgery + 400mL 2h before surgery	Nutricia Pre-op®, Nutricia, Zoetermeer, The Netherlands	Hunger; thirst; postoperative nausea and vomiting; glucose; insulin; cortisol; bowel movement onset; length of stay; other wellbeing/comfort symptoms
19	Yagmurdu r et al./2011[31]	Turkey	44	I: 45±7 C: 43±8	Abdominal	800mL 12.5% CHO drink evening before surgery + 400mL 90min before anaesthesia	fasting since midnight	-	Nutricia Preop®; Numico, Zoetermeer, the Netherlands	Hunger; thirst; nausea; pain; other wellbeing/comfort symptoms; glucose; insulin; haemodynamic parameters
20	Dock- Nasciment o et al./2012[32]	Brazil	36	42[18-62]	Abdominal	400mL 12.5% CHO drink 8h before anaesthesia + 200mL 2h before anaesthesia	fasting for 8h	C+G†: 400mL 12.5% CHO drink + glutamine 8h before anaesthesia + 200mL 2h before anaesthesia	NidexÒ, Nestlé, São Paulo, Brazil	Glucose; insulin; gastric residual volume
21	Feguri et al./2012[33]	Brazil	40	I: 56.6±6.56 P: 60.5±7.25	Cardiac	400mL 12.5% CHO 6h before anaesthesia + 200mL 2h before	-	400mL water 6h before anaesthesia + 200mL 2h	Unspecified	Glucose; insulin; postoperative complications; mortality; length
						anaesthesia		before anaesthesia		of stay; hunger; thirst; postoperative nausea and vomiting; vasoactive drug use; ventilation; atrial fibrillation
22	Harsten et al./2012[34]	Sweden	60	I: median 69 (range 45-80) P: 71(58-79)	Orthopaedics	400mL 12.5% CHO drink 1.5h before surgery + 400mL 2h after surgery	-	400mL flavoured water 1.5h before surgery + 400mL 2h after surgery	Nutricia Preop®; Numico, Zoetermeer, the Netherlands	Pain; hunger; thirst; nausea; glucose; biochemical markers; cognitive function; length of stay; complications; other wellbeing/comfort symptoms
23	Ljunggren et al./2012[35]	Sweden	60	I: 65.2±8 P: 66.4±10.6 C: 68.5±9.6	Orthopaedics	800mL of CHO drink evening before surgery + 400mL 2h before surgery	fasting since midnight	800mL tap water 2h before surgery	PreopR, Nutricia, Nordica AB, Stockholm, Sweden	Glucose; insulin; cortisol; urinary 3-methylhistidine; postoperative complications; other wellbeing/comfort symptoms
24	Yang et al./2012[36]	China	60	I: 63.38±9.07 P: 62.58±10.22	Abdominal	500mL 10% CHO drink 2-3h before anaesthesia	-	500mL sweetened water 2-3h before anaesthesia	Unspecified	Glucose; insulin; postoperative complications; length of stay
25	Belitova et al./2013[37]	Bulgaria	50	I: 52.9(27,77) C: 54.4(23,76)	Head and neck	800mL 12.5% CHO drink between 22:00 and 23:00 evening before surgery + 400mL 2h before surgery	small amount of water or tea up to 12h before surgery	-	Nutricia Pre-op®, Nutricia, Zoetermeer, The Netherlands	Residual gastric volume; insulin; glucose; creatinine; CRP; hunger; thirst; other wellbeing/comfort symptoms
26	Lidder et al./2013[38]	United Kingdom	120	I: 69(64,73.8) P: 73(63.8,81)	Abdominal	400mL of CHO drink 2h before surgery + 400mL flavoured water post surgery	-	400mL of flavoured water 2h before surgery + 400mL post surgery	Nutricia Preop®; Numico, Zoetermeer, the Netherlands	Glucose; insulin; handgrip strength; pulmonary function; intestinal permeability; postoperative complications
27	Tran et al./2013[39]	Canada	38	I: 59(50,67) C: 59(52,64)	Mixed	800mL 12.5% CHO water between 21:00 and 23:00 evening	fasting after 20:00 evening before	-	Nutricia Pre-op®, Nutricia, Zoetermeer, The	Insulin; blood glucose; β-cell function; adiponectin; free
						before surgery + 400mL 2h before surgery	surgery		Netherlands	fatty acids; IL-6; CRP; length of stay; hunger; thirst; pain; other wellbeing/comfort symptoms
28	Yildiz et al./2013[40]	Turkey	60	I: 47.63±8.83 C: 43.56±9.82	Abdominal	800mL 12.5% CHO drink evening before surgery + 400mL 2-3h before surgery	fasting for 8h	-	Nutricia Preop®; Numico, Zoetermeer, the Netherlands	Hunger; thirst; nausea; glucose; haemodynamic parameters; gastric volume; gastric pH; satisfaction; other wellbeing/comfort symptoms
29	Yilmaz et al./2013[41]	Turkey	40	I: 42.57±14.42 C: 45.73±10.385	Abdominal	400mL 12.5% CHO drink 2h before surgery	fasting for 8h	-	Nutricia Pre-op®, Nutricia, Zoetermeer, The Netherlands	Anxiety; residual gastric volume; gastric pH; postoperative nausea and vomiting; antiemetic use
30	Canbay et al./2014[42]	Turkey	50	I: 60±10.37 C: 58.36±11.19	Urological	800mL 12.5% CHO drink 00:00 evening before surgery + 400mL	fasting since midnight	-	Nutricia Pre-op®	Glucose; insulin; procalcitonin; anxiety; hunger; thirst; nausea;
						2h before surgery				haemodynamic parameters; wellbeing/comfort symptoms
31	Ljunggren et al./2014[43]	Sweden	23	I: 66 (range: 57- 75) P: 68 (range: 57- 76)	Orthopaedics	800mL of CHO drink at bedtime + 400mL 2h before surgery	-	800mL of lemon flavoured tap water at bedtime + 400mL 2h before surgery	Pre-op; Nutricia; Nordica AB, Stockholm, Sweden	Insulin; glucose
32	Raksakieti sak et al./2014[44]	Thailand	100	I: 69.8±7.3 C: 70.8±8.5	Orthopaedics	400mL 10% CHO drink between 18:00 and 00:00 evening before surgery + 400mL 2h before anaesthesia	fasting since midnight	-	Greenmate® orange juice	Hunger; thirst; anxiety; nausea; postoperative nausea and vomiting; hypotension; glucose; antiemetic and analgesic use; blood loss; length of stay; complications
33	Sada et al./2014[45]	Kosovo	162	Cholecystectomy: I: 55.8±13.5 P: 54.8±15.1	Abdominal	800mL 12.5% CHO drink 22:00 evening before	standard preoperative fasting	800mL non-caloric colourless	Nutricia preOp, Nutricia Ltd., Wiltshire, UK	Hunger; thirst; other wellbeing/comfort
				C: 59.1±12 Colorectal: I: 57.9±12 P: 56.6±13 C: 53.8±15.8		surgery + 400mL 2h before anaesthesia		liquid 22:00 evening before surgery + 400mL 2h before anaesthesia		symptoms; SAPS-II; length of stay
34	Webster et al./2014[46]	Australia	46	I: 54.5 (SD 36.0, 79.0) C: 61.0 (SD 27.0, 77.0)	Abdominal	800mL of CHO drink between 19:00 and midnight on evening before surgery + 200mL at 05:00 on day of surgery	fasting since midnight for solid and clear fluid up to 05:00 on day of surgery	-	Unspecified	Time to flatus; return of gastrointestinal function; mortality; adverse events; length of stay
35	Asakura et al./2015[47]	Japan	150	I: 63.4±13.6 C: 64.5±10.4	Unclear (surgery of body surface)	250mL 18% CHO drink between 06:00 and 06:30 morning of surgery	fasting since midnight	-	Arginaid WaterTM, Nestle Health Science, Tokyo, Japan	Postoperative nausea and vomiting; aspiration; body temperature; wellbeing/comfort symptoms
36	Azagury et al./2015[48]	Switzerla nd	203	Male: I: 42.4±11.7 C: 42.1±10.6 Female: I: 41.1±10.5 C: 42.4±10.8	Abdominal	800mL 12.5% CHO drink 12h before surgery + 400mL 2h before surgery	fasting since midnight	-	Nutricia Pre-op®, Nutricia, Zoetermeer, The Netherlands	Lean body mass; body weight loss; postoperative complications; length of stay
37	Pędziwiatr et al./2015[49]	Poland	43	I: 53.7±15.29 P: 55±9.55	Abdominal	400mL 12.5% CHO drink 2h before surgery	-	400mL clear water 2h before surgery	Nutricia Pre-op®	Glucose; insulin; cortisol; postoperative complications; length of stay
38	Singh et al./2015[50]	India	120	I: 43.2±15.85 P: 43.72±15.4 C: 44.4±11.45	Abdominal	400mL 12.5% CHO drink between 20:00 and 22:00 evening before surgery + 200mL 06:00 morning of surgery	fasting since midnight	400mL flavoured water between 20:00 and 22:00 evening before surgery + 200mL 06:00 morning of surgery	Unspecified	Postoperative nausea and vomiting; pain
39	Çeliksular et al./2016[51]	Turkey	80	General anaesthesia: I: 52.7±15.21 C: 47.95±16.28 Epidural: I: 53.3±14.69 C: 57.65±18.05	Orthopaedics	800mL 12.5% CHO drink 8h before surgery + 400mL 2h before surgery	fasting for 8h	-	PreopQ, Nutricia, Holland	Glucose; insulin; cortisol; inflammatory markers; haemodynamic parameters; blood loss/transfusion; pain; postoperative nausea and vomiting
40	Karlsson et al./2016[52]	Sweden	90	I: 40±2 P: 43.7±1.7	Abdominal	800mL CHO drink 16h before surgery + 400mL 2h before surgery	-	800mL water 16h before surgery + 400mL 2h before surgery	Nutricia Pre-op®	Pain; nausea; tiredness; headache
41	Çakar et al./2017[53]	Turkey	90	I: 48.17±9.81 C: 50.07±9.95	Head and neck	800mL 12.5% CHO drink at 00:00 + 400mL 2h before surgery	fasting since midnight	-	Nutricia Pre-op®	Hunger; thirst; perioperative vital signs; glucose; postoperative nausea and vomiting; pain; other wellbeing/comfort symptoms
42	Dilmen et al./2017[54]	Turkey	43	I: 48.95±11.51 C: 45.25±7.23	Spine	800mL 12.5% CHO drink between 21:00 and 00:00 evening before surgery + 400mL 2h before surgery	fasting for 8h	-	Nutricia Pre-op®	Glucose; insulin; cortisol; inflammatory markers; postoperative nausea and vomiting
43	Feguri et al./2017[55]	Brazil	60	I: 60.86±10.55 P: 63.43±8.56	Cardiac	200mL 12.5% CHO drink 2h before anaesthesia	-	200mL water before anaesthesia	Unspecified
44	Lee et al./2017[56]	Korea	60	I: 64±8 C: 65±9	Cardiac	400mL 12.8% CHO between 21:00 and 23:00 evening before surgery + 400mL 2-3h before surgery	fasting since midnight	-	NO-NPO, Daesang WelLife, Seoul, Korea	Glucose; insulin; free fatty acids; inflammatory markers; cardiac injury markers
45	Şavluk et al./2017[57]	Turkey	152	I: 59±11 F: 57±12	Cardiac	800mL 12.5% CHO drink 8h before surgery + 400mL 2h before surgery I2: 400mL 12.5% CHO drink 8h before surgery I3: 400mL 12.5% CHO drink 2h before surgery	fasting for 8h	-	Nutricia PreOp, Pfrimmer Nutricia GmbH, Germany	Insulin; glucose; inotrope/vasopress or requirement; ventilation; length of stay; hunger; nausea; other wellbeing/comfort symptoms
46	Doo et al./2018[58]	Korea	50	I: 49.8±7.1 C: 51±7.5	Head and neck	400mL 12.8% CHO drink 2h before anaesthesia	fasting since midnight	-	Nucare NONPO®, Daesang Wellife, Korea	Hunger; thirst; other wellbeing/comfort symptoms; postoperative nausea and vomiting; satisfaction; glucose; fasting time
47	Esaki et al./2018[59]	Japan	23	I: 43±13 P: 42±13	Head and neck	overnight fast followed by 278mL of 18% CHO water 2h before surgery	-	overnight fast followed by 278mL of mineral water 2h before surgery	Unspecified	Ketone bodies; free fatty acids; blood glucose; insulin; cortisol; noradrenaline; respiratory quotient
48	Fard et al./2018[60]	Iran	120	I: 30.2±3.37 P: 29.45±3.52	Caesarean section	800mL 12.5% CHO drink between 20-24h before surgery + 400mL 2h before anaesthesia	-	800mL flavoured water between 20-24h before surgery + 400mL 2h before anaesthesia	Nutricia Preop®; Numico, Zoetermeer, the Netherlands	Effect on breastfeeding
49	Gianotti et al./2018[61]	Italy	880	I: 68(58,75.5) P: 67(57,75)	Abdominal	800mL 12.6% CHO drink between 20:00 evening and 2h before surgery	-	800mL plain water between 20:00 evening and 2h before surgery	PeriOp, Nutricia, Milan, Italy	Postoperative infection; glucose; insulin
50	Hamamot o et al./2018[62]	Japan	70	I: 71[43-84] C: 69[49-85]	Abdominal	500mL 18% CHO drink evening	fasting with clear fluid	-	Arginaid Water®, Nestle	Intraoperative core temperature;
						before surgery + 250mL 2h before induction ± 250mL 2h before induction if surgery in afternoon	up to 2h before induction		Health Science, Kobe, Japan	short-term clinical outcomes; body composition
51	Lee et al./2018[63]	Korea	153	I: 49±12 P: 48±12 C: 50±13	Abdominal	400mL 12.8% CHO water between 20:00 and 22:00 evening before surgery + 400mL 2h before induction	fasting since midnight	400mL flavoured water between 20:00 and 22:00 evening before surgery + 400mL 2h before induction	Daesang WelLife Co., Ltd.	Quality of recovery; postoperative nausea and vomiting; pain; physical comfort; emotional state; physical independence; psychological support; haemodynamic response to positional change
52	Helminen et al./2019[64]	Finland	113	I: 47±13 C: 46±11	Abdominal	200mL of CHO drink by 06:00 for surgery scheduled at 08:00; or 08:00 for later surgery	fasting since midnight	-	Providextra; Fresenius Kabi Ab, Bad Homburg vor der Hohe, Germany	Thirst; hunger; nausea; pain; glucose; other wellbeing/comfort symptoms
53	Lende et al./2019[65]	Norway	80	Unspecified	Breast	400mL 12% CHO drink 18h before surgery + 400mL 2-4h before surgery	standard fasting with free intake of tap water	-	Pre-OpTM Nutricia, Netherlands	Tumour proliferation; glucose;insulin; IGF-1; IGFBP3; other wellbeing/comfort symptoms; clinical outcomes
54	Liu et al./2019[66]	China	120	Unspecified	Head and neck	400mL 12.5% CHO Drink 2h before surgery	fast for 8h prior to surgery	-	Maltodextrin Fructose Solution, SuQian®, Xi’an, China	Glucose; handgrip strength; pulmonary function; postoperative complications; length of stay
55	Morimoto et al./2019[67]	Japan	34	I: 40.5(28.25, 61) P: 31.5(24.75, 56)	Head and neck	no more than 250mL 18% CHO drink 2h before surgery	-	no more than 500mL plain water 2h before surgery	Arginaid Water; Nestle Health Science Co., Tokyo, Japan	Resting metabolic rate; total body water; ketone bodies; free fatty acids; insulin; glucose; 3-methylhistidine; retinol-binding protein; adiponectin; leptin
56	Onalan et al./2019[68]	Turkey	53	I: 53 IQR 16 C: 54 IQR 14	Abdominal	800mL 12.5% CHO drink at 00:00 + 400mL 2h before surgery	fasting since 00:00	-	Nutricia Pre-op®	Glucose; insulin; biochemistry; hunger; thirst; pain; anxiety; wellbeing/comfort symptoms
57	Rizvanovi ć et al./2019[69]	Bosnia and Herzegov ina	50	I: 61±7.3 C: 60.2±9.7	Abdominal	400mL 12.5% CHO drink at 22:00 evening before surgery + 200mL 2h before anaesthesia	fasted for 8h prior to surgery	-	Unspecified	Glucose; insulin; Glasgow Prognostic Score; IL-6; hunger; thirst; pain; return of gastrointestinal function; time to independent ambulation; postoperative discharge day; other wellbeing/comfort symptoms
58	Sokolic et al./2019[70]	Croatia	80	On pump: I: 68.5(59,74.5)	Cardiac	200mL 12.6% CHO drink 2h	standard preoperative	-	PreOp Nutricia, Dublin, Ireland	Peripheral lymphocyte
				C: 66(62,72) Off pump: I: 66(62,69) C: 67.5(61,72)		before surgery	fasting			subsets; NK/NKT cells; perforin expression
59	Wang et al./2019[71]	China	100	I: 57.5±2.3 C: 55.59±2.1	Abdominal	710mL of CHO drink evening before surgery + 355mL 2h before surgery	fasting for 10h	-	Unspecified	Hunger; thirst; other wellbeing/comfort symptoms; postoperative nausea and vomiting; gastric emptying; operation score; clinical outcomes
60	Wongying sinn et al./2019[72]	Thailand	70	I: 62.9±10.2 P: 62.7±9.7	Abdominal	800mL 12.5% CHO drink evening before surgery + 400mL 3h before anaesthesia	-	800mL pure water evening before surgery + 400mL 3h before anaesthesia	Unspecified	Walking capacity; glucose; insulin; nitrogen balance; length of stay; patient satisfaction
61	Al- Hirmizy et al./2020[73]	United Kingdom	80	I: 63.2{44-85} P: 61{38-83}	Gynaecologica l	800mL 12.6% CHO evening before surgery + 400mL 2h before anaesthesia	-	800mL flavoured water evening before surgery + 400mL 2h	Nutricia Clinical Care, Wiltshire, UK	Length of stay; pain; nausea and vomiting; return of gastrointestinal function;
								before anaesthesia		postoperative complications
62	Gök et al./2020[74]	Turkey	42	I: 46.76±11.01 C: 50±14.24	Abdominal	800mL 12.5% CHO water 8h before surgery + 200mL 2h before surgery	fasting since midnight	-	Unspecified	Thirst; hunger; dry mouth; nausea; vomiting; pain; abdominal distension; other wellbeing/comfort symptoms
63	Wendling et al./2020[75]	USA	67	Unspecified	Caesarean section	710mL 14% CHO drink evening before surgery + 355mL in morning of surgery	fasted for 8h prior to surgery	P†: 710mL commercial rehydration drink evening before surgery + 355mL in morning of surgery	Clearfast®; BevMD, Oceanside, CA, USA	Hunger; thirst; nausea; haemodynamic parameters; maternal complications; blood loss/transfusion; length of stay; infection; breastfeeding; neonatal glucose and complications; other wellbeing/comfort symptoms
64	Zhang et	China	58	I: 42.64±5.26	Gynaecologica	800mL 12.5%	fasting since	-	Nutricia	Phantom limb
	al./2020[76]			C: 43.57±5.60	l	CHO drink between 20:00 and 22:00 + 400mL 2h before surgery	midnight		Pre-op®, Nutricia, Zoetermeer, The Netherlands	syndrome; hunger; thirst; postoperative nausea and vomiting; glucose; insulin; IL-6; CRP; cortisol; lactate/pyruvate; handgrip strength; clinical recovery; length of stay; other wellbeing/comfort symptoms
65	Cho et al./2021[77]	Korea	88	I: 41.3±11.9 C: 38.9±10.9	Gynaecologica l	400mL 12.8% CHO drink midnight before surgery + 200mL 06:00 + 100mL up to 2h before surgery	fasting since midnight	-	NO-NPO®, Daesang WelLife Co., Ltd., Korea	Length of stay; satisfaction; pain; analgesic use; glucose; insulin
66	Clark et al./2021[78]	United Kingdom	209	I: 33±4.5 C: 33±4.84	Caesarean section	800mL 11.8% CHO drink evening before surgery + 400mL 06:00 on the day of surgery ± 400mL / 800mL if surgery later than 11:00 or 13:00 respectively	fasting since midnight for solid and fluid up to 06:00 day of surgery (09:00 if between 11:00 and 13:00 and 11:00 if after 13:00)	-	PreloadTM, Vitaflo International Ltd®	Urinary ketones; handgrip strength; anxiety; hunger; thirst; length of stay; adverse event
67	Gümüs et al./2021[79]	Turkey	68	I: 48.68±9.61 C: 42.38±9.27	Abdominal	400mL 12.5% CHO drink 2h before surgery	fasted for 12h	-	Unspecified	Glucose; insulin; cortisol; noradrenaline; adrenaline
68	He et al./2021[80]	China	90	I: 30(28.8,34) P: 31(29.5,34.5) C: 32(29,35.5)	Caesarean section	400mL 12.5% CHO drink 2h before surgery	fasting since 22:00 evening before surgery	400mL plain water 2h before surgery	Shu YuTM, Chongqing, China	Glucose; insulin; hunger; thirst; postoperative nausea and vomiting; time to flatus; fever; neonatal Apgar and glucose
69	Jeong et al./2021[81]	Korea	58	I: 73.3 ± 5.4 C: 73.9 ± 5.8	Urological	400mL 12.8% CHO drink 2h before anaesthesia	fasting since midnight	-	NO-NPO, Daesang WelLife Co., Ltd., South Korea	Gastric ultrasound grade; residual gastric volume; gastric pH; hunger; thirst; anxiety
70	Liu et al./2021[82]	China	120	I: 68.3±5.49 C: 69.2±6.55	Abdominal	200mL of CHO drink 2h before surgery	fasting for 8h for solid and 4h for liquid	-	ShuNeng; Yi Chang Ren Fu Pharmaceutical Co Ltd., China	Glucose; insulin; neonatal glucose; hunger; thirst; postoperative nausea and vomiting; time to flatus; abdominal distension; aspiration
71	Mousavie et al./2021[83]	Iran	95	I: 38±11 C: 41±13	Abdominal	200mL 12.5% CHO drink 2h before surgery	fasting since midnight	-	Unspecified	Postoperative nausea and vomiting; pain; quality of recovery; glucose
72	Rajan et al./2021[84]	India	52	I: 47.5±13.9 P: 15.6±13.0	Head and neck	250mL 15.6% apple juice 2h before surgery	-	250mL plain water 2h before surgery	Apple juice; brand unspecified	Glucose; haemodynamic parameters; postoperative nausea and vomiting
73	Suh et al./2021[85]	USA	176	I: 42.6±11.6 C: 43.9±11.2	Abdominal	296mL of CHO drink 20:00 night before surgery + 296mL 3h before surgery	fasting since midnight	-	Ensure before surgery	Length of stay; postoperative nausea and vomiting; antiemetic and analgesic use; glucose; postoperative complications; weight loss
74	Yang et al./2021[86]	China	120	I: 31.8±3.5 P: 32.4±4.1 C: 32.1±4.6	Caesarean section	300mL of CHO drink 2h before surgery	fasting since 20:00 for solid and 22:00 for liquid	300mL of distilled water 2h before surgery	ShuNeng, Humanwell, Yichang, China	Body temperature; intraoperative side effects/shivering
75	Liu et al./2021[87]	China	85	I: 34.63±5.14 P: 34.62±3.75	Caesarean section	300mL 7.5% CHO drink 2h before anaesthesia	-	300mL warm water 2h before anaesthesia	Unspecified	Postoperative complications; length of stay
76	Shi et al./2021[88]	China	75	I: 29.88±1.51 P: 29.36±1.52 C: 29.64±1.5	Caesarean section	300mL 14.2% CHO drink 2h before surgery	fasting for at least 6h	300mL water 2h before surgery	Renfu Farewell Pharmaceutical Company, China	Haemodynamic parameters; gastric antral cross-sectional area; hunger; thirst; anxiety; glucose; insulin
77	Chaudhar y et al./2022[89]	Nepal	66	I: 66.4±11.8 C: 69.3±13.9	Orthopaedics	100g of CHO evening before surgery + 50g 2h before surgery	fasting since midnight	-	Glucose-D, Nepali product	Pain; functional mobility; serum albumin
78	Cheng et al./2022[90]	China	120	I: 31.8±3.5 P: 32.4±4.1 C: 32.1±4.6	Caesarean section	300mL of CHO drink 2h before surgery	fasting on the day of operation	300mL of distilled water 2h before surgery	ShuNeng, Humanwell, Yichang, China	Time to colostrum; time to flatus; vomiting; pain; analgesic use; vaginal bleeding volume; postoperative complications
79	Choi et al./2022[91]	Korea	56	I: 71.9 ±4.8 C: 71.3 ±4.1	Orthopaedics	400mL 12.8% CHO drink 2-3h before anaesthesia	fasting with clear fluid up to 2h before anaesthesia	-	Unspecified	Handgrip strength; glucose; insulin; free fatty acids; glucagon/GLP-1; length of stay; postoperative nausea and vomiting; dizziness; hypotension; inflammatory markers; pain
80	Hosseini et al./2022[92]	Iran	260	I: 59.03±7.8 C: 57.7±7.9	Cardiac	dietitian-prescribed diet at 19:00, fasted for 6h, then received	dietitian-prescribed diet at 19:00, fasted for	-	Unspecified	Hospital length of stay; time to first intake; glucose; insulin;
						250mL 10% CHO drink 2h before surgery	12h			postoperative nausea and vomiting; pain; thirst; hunger; anxiety
81	Kadado et al./2022[93]	USA	153	I: 67.1 ±7.4 P: 65.3 ±10.2 C: 67.7 ±9.9	Orthopaedics	800mL 12.5% CHO drink evening before surgery + 400mL 3h before surgery	fasting since midnight	800mL lemon-flavored water evening before surgery + 400mL 3h before surgery	Nutricia Pre-op®	Length of stay; postoperative nausea and vomiting; pain; glucose; analgesic use; fluid bolus; adverse events; readmissions
82	Lee et al./2022[94]	Korea	50	I: 70.3±6.8 C: 70.5±6	Orthopaedics	400mL 12.8% CHO drink 2-3h before anaesthesia	fasting since midnight	-	NO-NPO, Daesang WelLife, Seoul, Korea	Glucose; insulin; free fatty acids; glucagon; GLP-1; C-peptide; length of stay; postoperative nausea and vomiting; dizziness; hypotension; delirium; wound infection; inflammatory
										markers; pain; gastric ultrasound; aspiration
83	Li et al./2022[95]	China	63	I: 62(55,66) C: 68(62,73)	Abdominal	CHO drink at 22:00 evening before surgery + 06:00 day of surgery (individualised volume of CHO drink prescribed by an endocrinologist)	fasting from 22:00 for solid and clear fluid up to 06:00 day on of surgery	-	Unspecified	Time to flatus; hunger; thirst; fatigue; postoperative nausea and vomiting; hypotension; adverse events
84	Lin et al./2022[96]	China	80	I1: 65.6±9.5 I2: 57.4±9.6 I3: 62.1±10.9 C: 62.0±8.8	Unclear (surgeries under general anaesthesia)	I1: 100mL 14.2% CHO drink 2h before induction I2: 200mL 14.2% CHO drink 2h before induction I3: 300mL 14.2% CHO drink 2h before induction	did not receive CHO drink	-	Yichang Human Medical Food Co., Ltd.	Gastric volume; Perlas grade; blood glucose; risk of reflux and aspiration
85	Tavalaee et al./2022[97]	Iran	95	Unspecified	Abdominal	800mL 12.5% CHO drink evening before surgery + 400mL	standard preoperative fasting	-	Unspecified	Pain; glucose; insulin; cortisol; albumin; CRP; wound infection;
						2-4h before surgery				drain fluid output
86	Kotfis et al./2023[98]	Poland	148	I: 31(28, 36) C: 34(29, 36)	Caesarean section	200 mL 12.5% CHO drink 2h before surgery	standard fasting (6h for solid foods and 2h for clear liquids)	-	Nutricia Pre-op®, Nutricia, Zoetermeer, The Netherlands	Postoperative nausea and vomiting; gastrointestinal recovery; maternal lactate; β-hydroxybutyrate; glucose; insulin; urinary N; neonatal glucose
87	Rizvanovi ć et al./2023[99]	Bosnia and Herzegov ina	60	I: 60.9±6.8 C: 59.93±9.31	Abdominal	400mL 12.5% CHO drink at 22:00 evening before surgery + 200mL 2h before anaesthesia	fasting since midnight	-	Nutricia Pre-op®, Nutricia, Zoetermeer, The Netherlands	Inflammatory markers; postoperative complications; readmission
88	Vishak et al./2023[100]	India	240	I-DM: 46±10.19 I-NDM: 41.3±12.9 P-DM: 47.7±9.5 P-NDM: 37.3±9.3	Abdominal	I-DM: 400mL of CHO drink 2h before surgery I-NDM: 400mL of CHO drink 2h before surgery	-	P-DM: 400mL of plain water 2h before surgery P-NDM: 400mL of plain water 2h before surgery	Unspecified	Glucose; insulin; haemodynamic parameters; gastric antral cross-sectional area; gastric volume; discomfort; thirst
89	Yadav et al./2023[101]	India	64	I: 42.53±8.88 C: 43.63±8.41	Abdominal	400mL 12.5% CHO drink 2h before surgery	standard fasting protocol (fast for 8h)	-	Unspecified	Glucose; insulin; cortisol; aspiration; adverse events
90	Boruah et al./2024[102]	India	60	I: 50.3±8.9 C: 51.1±9.2	Abdominal	800mL 12.5% CHO drink evening before surgery + 400mL 2-3h before surgery	fast for 8-10h for solids and 2h for clear fluids	-	Unspecified	Haemodynamic parameters; postoperative nausea and vomiting; pain; recovery scores; gastric volume
91	Kumar et al./2024[103]	India	72	I: 56.60±13.10 C: 52.20±13.90	Abdominal	400mL of 12.5% CHO drink 22:00 evening before surgery + 200mL 2h before surgery	fasted for 6-8h before surgery	-	Unspecified	Glucose; insulin; albumin; CRP; IL-6; Glasgow Prognostic Score; hunger; thirst; other wellbeing/comfort symptoms; pain; postoperative nausea and vomiting; return of gastrointestinal function; independent ambulation; morbidity; length of stay
92	Sharma et al./2024[104]	India	120	I: 30.07±4.69 P: 29.72±4.29	Caesarean section	400mL of CHO drink 2h before surgery	-	400mL of filtered water 2h before surgery	Glucon-D powder	Ketonuria; hunger; thirst; anxiety; dominant handgrip strength; recovery score
93	Tang et al./2024[105]	China	100	I: 29.15±9.32 C: 28.16±7.43	Head and neck	4mL/kg of 14.2% CHO drink 2-3h before anaesthesia	fasting since midnight	-	Outfast, Yichang Humanwell FSMP CO., LTD, Yichang, China	Hunger; thirst; postoperative nausea and vomiting; sleep quality; satisfaction; other wellbeing/comfort symptoms
94	Varughese et al./2024[106]	India	50	I: 59.08±10.25 P: 58.7±8.29	Unclear (surgeries under general anaesthesia)	400mL 12.5% CHO drink 3h before surgery	-	400mL flavoured water 3h before surgery	Unspecified	Glucose; residual gastric volume; gastric pH; hunger; thirst; postoperative vomiting
95	Wang et al./2024[107]	China	167	I: 42.6±10.2 C: 39.4±9.9 C-EOF: 43.1±11.9	Gynaecologica l	200mL 12.5% CHO drink up to 2h before anaesthesia	fasting for 6-8h before surgery	C-EOF†: 200mL 12.5% CHO drink up to 2h before anaesthesia + chewing gum after awakening from anaesthesia + 200mL 6h after surgery	Unspecified	I-FEED score; return of gastrointestinal function; dietary tolerance; postoperative nausea and vomiting; pain; postoperative complications; satisfaction; functional recovery; length of stay
96	Yap et al./2024[108]	Malaysia	34	I: 78(2.2) † C: 77.5(1.9) †	Orthopaedics	237mL 22.6% CHO drink 16:00 and 20:00 day before surgery + 237mL 2-6h before surgery	fast for 6h for solids and 2h for clear fluids	-	Unspecified	Recruitment rate; attrition rate; compliance; drink tolerability; adverse events; postoperative nausea and vomiting; pain; fatigue; length of stay; postoperative complications
97	Dulger et al./2025[109]	Turkey	84	I: 27.95±4.61 P: 29.76±4.58	Caesarean section	400mL 25% CHO drink evening before surgery + 200mL 2h before anaesthesia	-	400mL distilled water evening before surgery + 200mL 2h before anaesthesia	Nutricia-Fantomalt	Thiol/disulphide homeostasis; ischemia-modified albumin; gastric volume; gastric antral cross-sectional area; haemodynamic parameters; fetal blood gas
98	Lai et al./2025[110]	China	90	I1: 65±7.8 I2: 67±9.5 P: 67±7.9	Orthopaedics	I1: 400mL 12% CHO drink 2h before surgery I2: 400mL 12% CHO drink 4h before surgery	-	400mL warm water 4h before surgery	Unspecified	Glucose; insulin; aspiration; wound complications; length of stay; hunger; thirst; postoperative nausea and vomiting; satisfaction; mortality; readmission

^*Results reported as mean±standard deviation, mean {range}, median (25^th quartile, 75^th quartile), median [range]

^†Reported as mean (standard error of mean)

Note: Only study arms relevant to the predefined review questions and included in the quantitative synthesis are presented in this table. Additional intervention arms that were not analysed were not included in this table for clarity.

Abbreviations: CHO- Carbohydrate; I- Intervention group; P- Placebo group; C- Control group; DM- Diabetic; NDM- Non-diabetic; IGF-1- Insulin-like growth factor 1; CRP- C-reactive protein; HbA1c- Glycated haemoglobin; pH- Potential of hydrogen; IL-6- Interleukin-6; SAPS-II- Simplified Acute Physiology Score changes; IGFBP-3-Insulin-like growth factor-binding protein 3; NK/NKT cells- Natural killer/natural killer T cells; GLP-1- Glucagon-like peptide 1; C-peptide- Connecting peptide; I-FEED-Intake, Feeling nauseated, Emesis, physical Exam, and Duration of symptoms

Table 1.

Data analysis of primary and secondary outcomes

Outcomes	Trials	n	I2 (%)	MD/RR (95% CI)	P
1 PONV	21	1709	58	0.74 (0.58-0.94)	0.02
1.1 PONV – subgroup analysis CHO vs Fasting	13	1018	52	0.79 (0.59-1.07)	0.13
1.2 PONV – subgroup analysis CHO vs Placebo 1.3 Sensitivity analysis – only low risk of bias	11 7	795 490	61 8	0.62 (0.42-0.92) 1.06 (0.84-1.33)	0.02 0.63
2 Pre-operative hunger	20	1802	100	-1.56 (-2.57- -0.55)	0.003
3 Pre-operative thirst	19	1642	99	-1.61 (-2.35 - -0.88)	<0.001
4 Post-operative pain	19	1756	92	-0.43 (-0.71 - -0.15)	0.003
5 Length of hospital stay (days)	46	4787	85	-0.40 (-0.59 - -0.21)	<0.001
6 Residual gastric volume (mL)	12	1528	84	1.02 (-1.37 – 3.41)	0.40
7 Post-operative glucose (mg/dL)	30	2267	78	-3.45 (-6.64 - -0.25)	0.03
8 Insulin resistance, HOMA-IR	15	1026	96	-1.21 (-1.70 - -0.72)	<0.001

PONV: Post-operative nausea and vomiting; HOMA-IR: Homeostatic model assessment for insulin resistance; MD: Mean difference; RR: Risk ratio; CI: Confidence interval; CHO: Carbohydrate loading. A two-tailed P<0.05 was considered statistically significant

Table 2.

Summary of findings

Outcomes	Anticipated absolute effects* (95% CI)		Relative effect (95% CI)	№ of participants (studies)	Certainty of the evidence (GRADE)	Comments
	Risk with control	Risk with Pre-op Carb Loading
PONV	35 per 100	26 per 100 (20 to 33)	RR 0.74 (0.58 to 0.94)	1709 (21 RCTs)	⨁⨁◯◯ Low	Pre-operative oral carbohydrate loading may reduce post-operative nausea and vomiting.
Hunger Scale from: 0 to 10	The mean Hunger was 3.63	MD 1.56 lower (2.57 lower to 0.55 lower)	-	1802 (20 RCTs)	⨁⨁◯◯ Low	Pre-operative oral carbohydrate loading may reduce pre-operative hunger.
Thirst Scale from: 0 to 10	The mean Thirst was 3.76	MD 1.61 lower (2.35 lower to 0.88 lower)	-	1642 (19 RCTs)	⨁⨁◯◯ Low	Pre-operative oral carbohydrate loading may reduce pre-operative thirst.
Pain Scale from: 0 to 10	The mean Pain was 4	MD 0.43 lower (0.71 lower to 0.15 lower)	-	1756 (19 RCTs)	⨁⨁◯◯ Low	Pre-operative oral carbohydrate loading may reduce post-operative pain.
Length of Stay assessed with: day	The mean length of Stay was 7.3 days	MD 0.4 days lower (0.59 lower to 0.21 lower)	-	4787 (46 RCTs)	⨁⨁◯◯ Low	Pre-operative oral carbohydrate loading may reduce length of hospital stay, although the effect is small.
Residual Gastric Volume assessed with: mL	The mean Residual Gastric Volume was 23.9 mL	MD 1.02 mL higher (1.37 lower to 3.41 higher)	-	1528 (12 RCTs)	⨁◯◯◯ Very low	The effect of pre-operative oral carbohydrate loading on residual gastric volume is uncertain.
Glucose assessed with: mg/dL	The mean Glucose was 115.85 mg/dL	MD 3.45 mg/dL lower (6.64 lower to 0.25 lower)	-	2267 (30 RCTs)	⨁⨁⨁◯ Moderate	Pre-operative oral carbohydrate loading probably reduces post-operative glucose levels.
Insulin resistance assessed with: HOMA-IR	The mean Insulin Resistance was 5.47	MD 1.21 lower (1.7 lower to 0.72 lower)	-	1026 (15 RCTs)	⨁⨁⨁◯ Moderate	Pre-operative oral carbohydrate loading probably reduces insulin resistance (HOMA-IR).

*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; MD: Mean difference; RCT: Randomised controlled trial; Pre-op: Preoperative; Carb: Carbohydrate; GRADE: Grading of Recommendations Assessment, Development and Evaluation; PONV: Postoperative nausea and vomiting; HOMA-IR: Homeostatic model assessment for insulin resistance; RR: Relative risk. GRADE Working Group grades of evidence. High certainty: We are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: We are moderately confident in the effect estimate: The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: Our confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect. Very low certainty: We have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of effect

Supplementary Table 5.

PRISMA abstract checklist

Topic	No.	Item	Reported?
TITLE
Title	1	Identify the report as a systematic review.	Yes
BACKGROUND
Objectives	2	Provide an explicit statement of the main objective(s) or question(s) the review addresses.	Yes
METHODS
Eligibility criteria	3	Specify the inclusion and exclusion criteria for the review.	Yes
Information sources	4	Specify the information sources (e.g. databases, registers) used to identify studies and the date when each was last searched.	Yes
Risk of bias	5	Specify the methods used to assess risk of bias in the included studies.	No
Synthesis of results	6	Specify the methods used to present and synthesize results.	No
RESULTS
Included studies	7	Give the total number of included studies and participants and summarise relevant characteristics of studies.	Yes
Synthesis of results	8	Present results for main outcomes, preferably indicating the number of included studies and participants for each. If meta-analysis was done, report the summary estimate and confidence/credible interval. If comparing groups, indicate the direction of the effect (i.e. which group is favoured).	Yes
DISCUSSION
Limitations of evidence	9	Provide a brief summary of the limitations of the evidence included in the review (e.g. study risk of bias, inconsistency and imprecision).	Yes
Interpretation	10	Provide a general interpretation of the results and important implications.	Yes
OTHER
Funding	11	Specify the primary source of funding for the review.	No
Registration	12	Provide the register name and registration number.	Yes

From: Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. MetaArXiv. 2020, September 14. DOI: 10.31222/osf.io/v7gm2. For more information, visit: www.prisma-statement.org

Supplementary Table 6.

PRISMA main checklist

Topic	No.	Item	Location where item is reported
TITLE
Title	1	Identify the report as a systematic review.	1
ABSTRACT
Abstract	2	See the PRISMA 2020 for Abstracts checklist	1,2
INTRODUCTION
Rationale	3	Describe the rationale for the review in the context of existing knowledge.	3
Objectives	4	Provide an explicit statement of the objective(s) or question(s) the review addresses.	3
METHODS
Eligibility criteria	5	Specify the inclusion and exclusion criteria for the review and how studies were grouped for the syntheses.	4,5
Information sources	6	Specify all databases, registers, websites, organisations, reference lists and other sources searched or consulted to identify studies. Specify the date when each source was last searched or consulted.	4
Search strategy	7	Present the full search strategies for all databases, registers and websites, including any filters and limits used.	4
Selection process	8	Specify the methods used to decide whether a study met the inclusion criteria of the review, including how many reviewers screened each record and each report retrieved, whether they worked independently, and if applicable, details of automation tools used in the process.	4,5
Data collection process	9	Specify the methods used to collect data from reports, including how many reviewers collected data from each report, whether they worked independently, any processes for obtaining or confirming data from study investigators, and if applicable, details of automation tools used in the process.	4,5
Data items	10a	List and define all outcomes for which data were sought. Specify whether all results that were compatible with each outcome domain in each study were sought (e.g. for all measures, time points, analyses), and if not, the methods used to decide which results to collect.	4,5
	10b	List and define all other variables for which data were sought (e.g. participant and intervention characteristics, funding sources). Describe any assumptions made about any missing or unclear information.	4,5
Study risk of bias assessment	11	Specify the methods used to assess risk of bias in the included studies, including details of the tool(s) used, how many reviewers assessed each study and whether they worked independently, and if applicable, details of automation tools used in the process.	4,5
Effect measures	12	Specify for each outcome the effect measure(s) (e.g. risk ratio, mean difference) used in the synthesis or presentation of results.	4,5
Synthesis methods	13a	Describe the processes used to decide which studies were eligible for each synthesis (e.g. tabulating the study intervention characteristics and comparing against the planned groups for each synthesis (item 5)).	4,5
	13b	Describe any methods required to prepare the data for presentation or synthesis, such as handling of missing summary statistics, or data conversions.	4,5
	13c	Describe any methods used to tabulate or visually display results of individual studies and syntheses.	4,5,6
	13d	Describe any methods used to synthesize results and provide a rationale for the choice(s). If meta-analysis was performed, describe the model(s), method(s) to identify the presence and extent of statistical heterogeneity, and software package(s) used.	4,5,6
	13e	Describe any methods used to explore possible causes of heterogeneity among study results (e.g. subgroup analysis, meta-regression).	4,5,6
	13f	Describe any sensitivity analyses conducted to assess robustness of the synthesized results.	N/A
Reporting bias assessment	14	Describe any methods used to assess risk of bias due to missing results in a synthesis (arising from reporting biases).	4,5
Certainty assessment	15	Describe any methods used to assess certainty (or confidence) in the body of evidence for an outcome.	4,5,6
RESULTS
Study selection	16a	Describe the results of the search and selection process, from the number of records identified in the search to the number of studies included in the review, ideally using a flow diagram.	7
	16b	Cite studies that might appear to meet the inclusion criteria, but which were excluded, and explain why they were excluded.	7
Study characteristics	17	Cite each included study and present its characteristics.	7
Risk of bias in studies	18	Present assessments of risk of bias for each included study.	7
Results of individual studies	19	For all outcomes, present, for each study: (a) summary statistics for each group (where appropriate) and (b) an effect estimate and its precision (e.g. confidence/credible interval), ideally using structured tables or plots.	8,9
Results of syntheses	20a	For each synthesis, briefly summarise the characteristics and risk of bias among contributing studies.	8,9
	20b	Present results of all statistical syntheses conducted. If meta-analysis was done, present for each the summary estimate and its precision (e.g. confidence/credible interval) and measures of statistical heterogeneity. If comparing groups, describe the direction of the effect.	8,9
	20c	Present results of all investigations of possible causes of heterogeneity among study results.	8,9
	20d	Present results of all sensitivity analyses conducted to assess the robustness of the synthesized results.	8
Reporting biases	21	Present assessments of risk of bias due to missing results (arising from reporting biases) for each synthesis assessed.	7,8
Certainty of evidence	22	Present assessments of certainty (or confidence) in the body of evidence for each outcome assessed.	7,8,9
DISCUSSION
Discussion	23a	Provide a general interpretation of the results in the context of other evidence.	10,11,12,13,14
	23b	Discuss any limitations of the evidence included in the review.	10,11,12,13,14
	23c	Discuss any limitations of the review processes used.	14,15
	23d	Discuss implications of the results for practice, policy, and future research.	14,15
OTHER INFORMATION
Registration and protocol	24a	Provide registration information for the review, including register name and registration number, or state that the review was not registered.	4
	24b	Indicate where the review protocol can be accessed, or state that a protocol was not prepared.	4
	24c	Describe and explain any amendments to information provided at registration or in the protocol.	N/A
Support	25	Describe sources of financial or non-financial support for the review, and the role of the funders or sponsors in the review.	First page file
Competing interests	26	Declare any competing interests of review authors.	First page file
Availability of data, code and other materials	27	Report which of the following are publicly available and where they can be found: template data collection forms; data extracted from included studies; data used for all analyses; analytic code; any other materials used in the review.	First page file

From: Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. MetaArXiv. 2020, September 14. DOI: 10.31222/osf.io/v7gm2. For more information, visit: www.prisma-statement.org

Twenty-one RCTs (n = 1709) measured PONV outcome, and pooled analysis demonstrated that pre-operative oral carbohydrate loading significantly reduced the incidence of PONV (RR 0.74 95% confidence interval (CI) 0.58–0.94, P = 0.02, I² = 58 %, level of evidence = low) [Figure 2]. The funnel plot for PONV shows asymmetry, suggesting small-study effects or publication bias [Supplementary Figure 2 ^{(398.8KB, tif)} ].

Figure 2.

Primary outcome: Post-operative nausea and vomiting. CI: Confidence interval; df: Degree of freedom

In the subgroup analysis of overnight fasting and oral placebo, our pooled data showed similar significant reduction in PONV in oral placebo groups (11 studies, n = 795 patients, RR 0.62 95% CI 0.42–0.92, P = 0.02, I² = 61%) [Figure 3]. However, in the overnight fasting group, although still favouring pre-operative oral carbohydrate loading in reducing PONV, the result was no longer statistically significant (13 studies, n = 1018 patients, RR 0.79 95% CI 0.59–1.07, P = 0.13, I² = 52%) [Figure 3]. Sensitivity analysis of RCTs with low risk of bias did not demonstrate a significant effect of carbohydrate loading on PONV (7 studies, n = 490 patients, RR = 1.06 95% CI 0.84–1.33, P = 0.63, I² = 8%) [Supplementary Figure 3 ^{(340.8KB, tif)} ].

Figure 3.

Subgroup analysis of post-operative nausea and vomiting: conventional fasting versus placebo comparators. CI: Confidence interval; df: Degree of freedom

In the trial sequential analysis, the required information size for PONV was 2041 patients. With 1709 patients, only 83.7% of the required information size was achieved to detect statistical significance of carbohydrate loading on PONV [Figure 4].

Figure 4.

Trial sequential analysis of incidence of post-operative nausea and vomiting. X-axis: the number of patients randomised; Y-axis: the cumulative Z-score; the blue cumulative Z-curve was constructed using a random-effects model. Red vertical line with diamonds: required information size of a meta-analysis. PONV: Postoperative nausea and vomiting

Twenty RCTs (n = 1802) reported pre-operative hunger score. Statistically significant reduction was found in the carbohydrate group from the pooled data analysis (MD -1.56 95% CI -2.57 to -0.55, P = 0.003, I² = 100%, level of evidence = low) [Supplementary Figure 4 ^{(600.2KB, tif)} ]. Nineteen RCTs (n = 1642) examined pre-operative thirst score. Data revealed a statistically significant reduction in the carbohydrate group compared to the control group (MD -1.61 95% CI -2.35 to -0.88, P < 0.001, I² = 99%, level of evidence = low) [Supplementary Figure 5 ^{(575.9KB, tif)} ]. Nineteen RCTs (n = 1756) measured post-operative pain score. Pooled data analysis revealed statistically significant difference between the carbohydrate versus control groups (MD -0.43 95% CI -0.71 to -0.15, P = 0.003, I² = 92%, level of evidence = low) [Supplementary Figure 6 ^{(573.9KB, tif)} ].

Forty-six RCTs (n = 4787) examined the length of hospital stay after surgery. The combined data revealed statistically significant reduction of hospital stay in the carbohydrate group (MD -0.40 95% CI -0.59 to -0.21, P < 0.001, I² = 85%, level of evidence = low) [Supplementary Figure 7 ^{(1.1MB, tif)} ]. Twelve RCTs (n = 1528) examined residual gastric volume. Pooled data analysis found no significant difference in the residual gastric volume between the carbohydrate versus control groups (MD 1.02 95% CI -1.37 to 3.41, P = 0.40, I² = 84%, level of evidence = very low) [Supplementary Figure 8 ^{(397.5KB, tif)} ].

Thirty RCTs (n = 2267) examined post-operative serum glucose level, which was statistically significant between the carbohydrate and control groups (MD -3.45 95% CI -6.64 to -0.25, P = 0.03, I² = 78%, level of evidence = moderate) [Supplementary Figure 9 ^{(776.6KB, tif)} ]. Fifteen RCTs (n = 1026) reported insulin resistance using the homeostatic model assessment for insulin resistance (HOMA-IR) equation. The carbohydrate group was found to have significantly reduced insulin resistance compared to the control group (MD -1.21 95% CI -1.70 to -0.72, P < 0.001, I² = 96%, level of evidence = moderate) [Supplementary Figure 10 ^{(484.7KB, tif)} ].

DISCUSSION

The current meta-analysis demonstrated that pre-operative oral carbohydrate loading was associated with a lower incidence of PONV in the main pooled analysis. In subgroup analysis, the reduction in PONV remained statistically significant in the placebo group but was not statistically significant in analysis comparing carbohydrate loading with conventional fasting. Furthermore, sensitivity analysis produced a neutral pooled estimate and did not support a significant reduction in PONV with pre-operative carbohydrate loading. In terms of secondary outcomes, carbohydrate loading reduced pre-operative thirst and hunger, as well as post-operative pain, insulin resistance, and serum glucose levels. However, no significant difference was detected in the residual gastric volume. The level of evidence ranged from very low to moderate, due to potential risk of bias, indirectness, imprecision, inconsistency, and dose–response relationship.

To the best of our knowledge, this is the most comprehensive review summarising the clinical evidence on the effect of pre-operative carbohydrate loading on the incidence of PONV in patients undergoing elective surgery. The main strengths of this review include an exhaustive literature search, and all included RCTs underwent rigorous appraisal of methodology and evidence quality using the GRADE approach. Compared with previous reviews by Ricci et al.,[111] Cheng et al.,[112] and Noba et al.,[113] our analysis included a larger body of evidence with additional trials published up to 2025. Earlier syntheses reported inconsistent findings, which may be attributable to significant degree of heterogeneity in outcome definitions and measurement approaches, including the use of non-uniform endpoints such as nausea alone, vomiting alone, or composite outcomes assessed at different time points.[17,26,30,73,85,111,112] By applying a standardised definition of PONV and standardising outcome reporting to a single 0–24 h incidence per study, we aimed to reduce variability and minimise duplication of outcome data across time points to improve comparability across studies.

For the purpose of this review, PONV is defined as any nausea, retching, or vomiting within 24 h of anaesthesia. It is multifactorial and may involve serotonin-mediated vagal signalling. Volatile agents and peri-operative opioids are established risk factors for PONV and may activate central emetic pathways involving the area postrema and nucleus of the tractus solitarius.[114] Surgical handling of the bowel can further trigger neurogenic and inflammatory pathways within the intestinal wall, contributing to impaired gastrointestinal motility leading to post-operative ileus.[115,116] Pre-operative carbohydrate loading is believed to attenuate the metabolic stress response, which can dampen inflammatory signalling in the gut wall. In addition, patients who are less metabolically stressed typically require lower peri-operative opioid doses, removing another well-known trigger for emesis.[2] However, given the non-significant sensitivity analysis, the conventional fasting subgroup, and the inconclusive trial sequential analysis due to the accrued sample size representing only 83.7% of the required information size, the extent to which carbohydrate independently reduces PONV remains uncertain. These inconsistent findings may be partly explained by the smaller number of studies included in the sensitivity analysis and by clinical and methodological heterogeneity across trials, including differences in surgical populations, types of surgery, anaesthetic choice, opioid exposure, carbohydrate regimen, and antiemetic prophylaxis.[33,44,47,55,77,91,110] In some studies, PONV may have been driven predominantly by factors such as spinal morphine, peri-operative opioids, volatile anaesthesia, or procedure-related inflammatory responses, which may not be directly modified by carbohydrate loading.[33,44,55] Whether any observed effect is mediated by carbohydrate content itself, reduced fasting duration, altered gastric emptying, reduced opioid exposure, or attenuation of surgical stress response could not be established from the current evidence.

The very high statistical heterogeneity observed for several pooled outcomes, namely, incidence of hunger, thirst, and insulin resistance (I² >90%), further reduces confidence in the summary estimates and most likely reflects genuine clinical heterogeneity in surgical population, different procedures, carbohydrate formulation, concentration, volume and timing of administration, anaesthetic and analgesic technique, and antiemetic prophylaxis, rather than chance alone. As many of the included trials were embedded within enhanced recovery pathways, the observed effects may represent the combined influence of shortened fasting, peri-operative fluid intake, and other co-interventions rather than the carbohydrate load in isolation, and the independent contribution of carbohydrate cannot be disentangled from the present data. The pooled estimates should therefore be regarded as hypothesis-generating and interpreted at the level of the overall intervention strategy rather than as precise, transferable effect sizes.

The effects of pre-operative oral carbohydrate loading on lowering pre-operative hunger and thirst scores are consistent with earlier reviews.[89,112,113] Notably, those syntheses detected no difference in thirst when pre-operative oral carbohydrate loading was compared with plain or flavoured water. Taken together, the evidence indicates that any fluid is sufficient to relieve thirst, whereas the presence of carbohydrate is required to reduce the sensation of hunger. For post-operative pain, our result differed from a previous review of 22 trials,[116] which found no evidence of oral carbohydrate loading in reducing post-operative pain. A RCT by Singh et al.[50] reported lower pain scores in patients who received pre-operative oral carbohydrate loading, which could possibly be due to reduction in surgical stress response as well as improvement in general well-being. However, this result should be interpreted with caution as the overall quality of evidence is very low. Although pain scores were harmonised and converted to a standardised 10-point scale where possible, the included trials used different rating scales including visual analogue score, numeric rating, and verbal rating scales, assessed at non-uniform time points, and involved procedures with very different baseline pain burdens and analgesic protocols, contributing to substantial degree of heterogeneity. Most studies were small and only partially blinded, so the observed benefit could reflect expectation or placebo effects rather than a true analgesic action. Moreover, the pooled reduction in pain score was small (an MD of less than half a point on a 10-point scale) and is unlikely to be clinically important in isolation, particularly given the low certainty of evidence. Our review also demonstrated that patients who received pre-operative oral carbohydrate loading were associated with a shorter length of hospital stay. While this result was similar to those of earlier studies, some confounding factors including patient’s demographic profile, comorbidities, and social situation could affect the total duration of hospitalisation.[111,112,117] The absolute reduction in length of stay was also modest (approximately 0.45 day); whether a difference of this magnitude is clinically meaningful for individual patients or health services is uncertain and should not be over-interpreted on the basis of statistical significance alone.

Several studies concluded no significant difference in residual gastric volume between the carbohydrate and control groups.[113,118,119] This finding was consistent with our review and suggested that it is safe to provide pre-operative oral carbohydrate loading 2 h before surgery. In our study, patients who received pre-operative oral carbohydrate loading had lower post-operative glucose levels and insulin resistance, which was in line with findings from previous reviews.[111] Surgical trauma induces a neuroendocrine stress response characterised by a surge of catecholamine release, hepatic glycogenolysis, and insulin resistance,[2] and pre-operative oral carbohydrate loading is thought to attenuate this response by maintaining patients in a metabolically “fed” state. It replenishes hepatic glycogen stores, promotes a modest increase in circulating insulin, and thereby reduces catecholamine-driven gluconeogenesis that typically follows prolonged fasting. As a result, peri-operative blood glucose levels may remain closer to euglycaemia, potentially blunting the insulin resistance response.[2,14] These metabolic effects provide a plausible explanation for the observed improvements in clinical outcomes. However, given the variability in evidence certainty across outcomes, this relationship should be interpreted with caution.

One major limitation of this meta-analysis was the marked heterogeneity in pre-operative oral carbohydrate loading regimens which may obscure any dose–response relationship in the pooled estimates. The asymmetry seen in the funnel plot for the primary outcome [Supplementary Figure 2 ^{(398.8KB, tif)} ] further raises the possibility of publication bias or small-study effects, which may have exaggerated the apparent benefit of pre-operative oral carbohydrate loading on PONV. It reinforces the need for cautious interpretation of this outcome. Potential confounding factors could not be fully adjusted for, including type of surgery, peri-operative care, anaesthetic regimens, patient baseline characteristics, and adjunctive use of different types of anti-emetics or opioids. Future trials should explore the use of pre-operative oral carbohydrate loading in diabetic patients with regular peri-operative glycaemic reading monitoring. As the present review was designed to compare carbohydrate loading versus placebo or conventional fasting, it could not determine the optimal carbohydrate regimen. Future trials and network meta-analyses comparing different formulations, concentrations, doses, and timing of pre-operative oral carbohydrate loading are needed to determine the most effective regimen. We were also unable to undertake several potentially informative subgroup analyses such as major versus minor surgery, abdominal versus non-abdominal surgery, enhanced recovery versus conventional pathways, and different pre-operative oral carbohydrate formulations due to inconsistent reporting across the included trials. These comparisons should be prioritised in future studies to help explain the observed heterogeneity and to identify the patient populations most likely to benefit. Long-term outcomes beyond discharge such as quality of life, return to normal activity, and readmission rates could be explored, and formal cost-effectiveness analysis could be performed to support health policy decisions.

CONCLUSION

In conclusion, pre-operative oral carbohydrate loading may reduce the incidence of PONV and improve pre-operative hunger and thirst, post-operative pain, and the length of hospital stay. However, given the low level of evidence, high degree of heterogeneity, non-significant sensitivity analysis, potential publication bias, and inconclusive trial sequential analysis, the effect on PONV should be interpreted cautiously and was not confirmed when the analysis was restricted to studies at low risk of bias. Several statistically significant secondary outcomes, including post-operative pain and length of stay, showed small absolute effects of uncertain clinical importance. Further adequately powered studies are warranted to standardise the dose and concentration of oral carbohydrate on homogeneous surgical patients.

Disclosure of use of artificial intelligence (AI)-assistive or generative tools

The authors confirm that AI tools or language models (LLM) have not been utilised in the manuscript, except that software has been used for grammar corrections.

Author contributions

KN: Conceptualisation, methodology, resources, writing - review and editing, supervision, validation. TC, EH: Methodology, data curation, formal analysis, writing - original draft, validation, visualisation. MBZ: Writing- review and editing, supervision.

Supplementary material

This article has supplementary material which can be accessed at the following link - https://links.lww.com/IJOA/A87.

Conflicts of interest

There are no conflicts of interest.

Online Supplementary Data

Supplementary Figure 1 ^{(4.4MB, tif)} Risk of bias assessment of included studies

Supplementary Figure 2 ^{(398.8KB, tif)} Funnel plot of Primary outcome: Post-operative nausea and vomiting

Supplementary Figure 3 ^{(340.8KB, tif)} Sensitivity analysis for post-operative nausea and vomiting including studies at low risk of bias

Supplementary Figure 4 ^{(600.2KB, tif)} Forest plot of Secondary outcome: Pre-operative hunger

Supplementary Figure 5 ^{(575.9KB, tif)} Forest plot of Secondary outcome: Pre-operative thirst

Supplementary Figure 6 ^{(573.9KB, tif)} Forest plot of Secondary outcome: Post-operative pain

Supplementary Figure 7 ^{(1.1MB, tif)} Forest plot of Secondary outcome: Length of hospital stay

Supplementary Figure 8 ^{(397.5KB, tif)} Forest plot of Secondary outcome: Residual gastric volume

Supplementary Figure 9 ^{(776.6KB, tif)} Forest plot of Secondary outcome: Post-operative glucose

Supplementary Figure 10 ^{(484.7KB, tif)} Forest plot of Secondary outcome: Insulin resistance

Supplementary Table 1 PICO Table

Supplementary Table 2 Search strategy for EMBASE, Ovid MEDLINE and CENTRAL databases

Supplementary Table 3 List of excluded studies

Supplementary Table 4 Clinical characteristics of included studies

Supplementary Table 5 PRISMA abstract checklist

Supplementary Table 6 PRISMA main checklist

Supplementary Figure 1

Risk of bias assessment of included studies

Supplementary Figure 2

Funnel plot for primary outcome: Post-operative nausea and vomiting

Supplementary Figure 3

Sensitivity analysis for post-operative nausea and vomiting including studies at low risk of bias

Supplementary Figure 4

Secondary outcome: Pre-operative hunger

Supplementary Figure 5

Secondary outcome: Pre-operative thirst

Supplementary Figure 6

Secondary outcome: Post-operative pain

Supplementary Figure 7

Secondary outcome: Length of hospital stay

Supplementary Figure 8

Secondary outcome: Residual gastric volume

Supplementary Figure 9

Secondary outcome: Post-operative glucose

Supplementary Figure 10

Secondary outcome: Insulin resistance

Funding Statement

Nil.