A Scoping Review of the Effect of Intermittent Fasting on Diabetes Regulation and Weight Control

Abstract

Introduction:

Intermittent fasting (IF) has emerged as a popular dietary approach that has gained popularity among individuals concerned with weight and diabetes control. This scoping review evaluated the effects of IF on glycaemic control and weight reduction by analysing various IF protocols.

Methods:

A scoping review was conducted according to PRISMA-ScR guidelines. The PubMed, Embase, Cochrane Library, and Medline databases were searched (2019–2024) for randomised controlled trials (RCTs) and observational studies. The primary outcomes were the effectiveness of IF on glycaemic control, measured by changes in fasting blood glucose (FBG), insulin sensitivity, and HbA1c. The secondary outcomes assessed the impact of IF on weight management.

Results:

The scoping review identified improvements in FBG levels and insulin sensitivity among individuals practicing IF, with HbA1c reductions observed in multiple studies. Weight loss and favourable changes in body composition have consistently been reported. The ethnic inequalities, particularly for South Asians, were also reported, revealing gaps in geographical evidence and proposing population-specific IF interventions. However, adherence challenges and adverse effects, such as hunger, fatigue, and irritability, were noted, highlighting the need for personalised IF protocols. Variability in outcomes due to individual factors such as age, gender, and baseline metabolic health was evident.

Conclusion:

IF is a promising strategy for glycaemic control and sustainable weight management in patients with diabetes mellitus. Despite its benefits, individualisation and medical supervision are crucial for addressing compliance issues and minimizing risks. The ethnic and cultural factors must be considered in ongoing clinical care and future IF research.

INTRODUCTION

Intermittent fasting (IF) is becoming popular owing to its potential use in weight management and blood sugar control. This is due to its flexible nature, which appeals to those who prefer fewer restrictions than conventional diabetes management.[1]

IF has been reported to have psychological effects such as weight reduction and strengthening of metabolic health. IF may help decrease stress on food choices and provide an individual with a sense of control, leading to better overall mental health.[2] Besides its ever-growing popularity, IF elicits doubts about its ultimate effects and threats. Although fasting periods might facilitate beneficial cellular health improvements through autophagy, some researchers maintain the necessity of attention for people with prior health complications due to their routines with prolonged fasting periods.[3]

Research has shown that IF has delivered mixed results, with some studies indicating that it improves glycaemic control and aids in weight loss; however, others have reported inconclusive or mixed outcomes.[4,5] Besides, despite the fact that IF brings a number of health advantages, it is not appropriate for every individual. Examples of such people are those with specific medical issues, such as type 1 diabetes mellitus (T1DM) or a previous history of eating disorders, who may suffer from fasting for longer periods of time.[6]

This study aimed to assess the effects of IF on diabetes control and weight management. This study aimed to investigate whether and how various IF strategies are linked to blood glucose levels, insulin sensitivity, and other indicators of glycaemic control.

MATERIALS AND METHODS

Research design

The study design was a scoping review of articles published on IF in the context of sustainable medical practices utilising the Preferred Reporting Items for Systematic Review and Meta-Analysis extension for scoping reviews (PRISMA-ScR) 2018 guidelines. After screening the literature, all the authors filtered the papers that met the eligibility criteria.

Eligibility criteria

The eligibility criterion for this scoping review was adults aged ≥18 years with a prior diagnosis of type 2 diabetes mellitus (T2DM). The inclusion criteria were articles published in English that conducted only randomised controlled trials (RCTs) and observational studies between 2019 and 2024, discussing IF and its effects on issues such as blood glucose levels or insulin sensitivity, and studies that considered IF and its effect on weight management. The exclusion criteria were studies falling outside the specified time interval (before 2019 or after 2024) and studies with a population group that included either non-type 2 forms of diabetes mellitus or pregnant women.

Search strategy and study selection

From 2019 to 03 November 2024, the authors searched for peer-reviewed papers and conference/abstract proceedings in three electronic databases: MEDLINE (the Ovid interface), EMBASE (the Ovid interface), and CENTRAL (the Cochrane Library). The authors also manually searched the primary registries for relevant RCTs, namely, ClinicalTrials.Gov, EU Clinical Trials Registers, and the WHO International Clinical Trials Registry Platform. We also conducted efforts and screened the references and citations of published papers for any possible additional studies. Additionally, grey literature was examined using open grey literature databases, and additional databases were identified for grey literature searches. Only studies published in English were included in this meta-analysis. Search strategies were developed using keywords, their synonyms, abbreviations, and MeSH terms for “intermittent fasting,” “T2DM,” “glucose,” “insulin,” “diabetic control,” and “weight control.” It was most appropriate for RCTs to be retrieved using search filters endorsed by the Cochrane Collaboration or a librarian.

During the pilot review phase, all publications retrieved were initially imported into Endnote 20 for the preliminary deduplication process. After the full text and any supporting materials were retrieved, the titles and abstracts were independently assessed by two independent reviewers (THK and XBL) using Rayyan Software in compliance with specified eligibility standards. The authors of the retrieved articles were contacted via e-mail to request for any missing data. Only accessible full-text publications were included in this review.

Study outcomes

The primary outcome of this scoping review was the evaluation of glycaemic control among individuals with T2DM practicing IF. This included the assessment of changes in fasting blood glucose levels, insulin sensitivity, and glycated haemoglobin (HbA1c) as key indicators of glucose regulation and diabetes management. The secondary outcomes focussed on the effect of IF on weight management, including reductions in body weight and improvements in body composition such as reduced fat mass and increased lean muscle mass. Additionally, this study aimed to discover adherence to various IF protocols and identify potential adverse effects such as hunger, fatigue, irritability, and other complications.

These outcomes were analysed to understand the therapeutic potential of IF and its practicality in long-term diabetes and weight management strategies. For efficacy (primary) outcomes, data were analysed according to the intention-to-treat (ITT) principle, ensuring that all randomised participants were included in the analysis as originally allocated. This review was conducted as a qualitative synthesis (scoping review) and not as a meta-analysis. We did not pool the data statistically; rather, we summarised the outcomes across RCTs and observational studies. Unlike systematic reviews and meta-analyses, scoping reviews typically describe the trends and gaps. (If the original text was unclear, we clarified that the findings were drawn from a descriptive synthesis rather than a new meta-analysis).

RESULTS

This review identified the role of IF in diabetes control and weight management through a comprehensive review that analysed the results of various IF protocols on blood glucose levels, insulin sensitivity, and other measures associated with glycemic control. The report further discussed the effect of IF on weight loss through changes in body composition and long-term viability of weight reduction. Finally, possible risks and compliance issues concerning IF were examined, which can be used as the basis for future investigations and may also be used to guide clinical applications in diabetes management and weight loss.

Effects on glycaemic control

The major result of the scoping review was that IF had positive effects on glycaemic control in T2DM patients. Compared to the control groups, which are based on traditional patterns, multiple studies have illustrated that alternate-day fasting and time-restricted feeding are related to a noteworthy decrease in fasting blood sugar levels.[7,8,9] Therefore, IF could be regarded as a feasible dietary strategy for controlling glucose levels [Table 1]. The IF intervention in one RCT showed that the fasting blood sugar levels of the participants decreased significantly at the end of 12 weeks, indicating the effectiveness of this type of fasting on normal glucose levels.[10] Another study investigating time-restricted eating reported comparable results. It was observed that the participants achieved lower blood glucose levels after they had followed the 8 h of eating and 16 h of fasting for 6 weeks.[11] However, we clarified that the literature is mixed, even though many trials report improved glycaemic control and weight loss with IF, but some meta-analyses found no overall difference compared to standard diets. For instance, a 2023 systematic review showed no significant difference in HbA1c or fasting glucose levels between IF and control diets across pooled RCTs. In contrast, a large 2024 Chinese RCT showed that a 5:2 meal-replacement IF diet achieved greater HbA1c reduction (–1.9%) than metformin or empagliflozin (–1.6%, –1.5%). To convey this, we note that IF often improves diabetes markers in trials, but overall, meta-analyses report only equivalence with continuous dieting. These conflicting data underscore the review’s conclusions that outcomes can vary by study design and population and reinforce the call for further head-to-head studies.[12,13] A summary of the positive effects of IF on glycaemic control and weight is provided in Table 2.

Table 1.

Summary of the most common IF methods discussed in the literature, including time-restricted feeding, a 5:2 Diet, Alternate-Day Fasting (ADF), and Periodic Fasting/FMD

IF Regimen	Pattern Description	Notes/Effects
Time-Restricted Feeding (TRF)	Daily 14–20 h fast (e.g. 16/8)	High adherence; improves fasting glucose and weight via circadian timing.
5:2 Diet	5 days normal eating, 2 non-consecutive days/week ≤800 kcal	Easier weekly structure but often lower compliance; can significantly reduce HbA1c and weight.
Alternate-Day Fasting (ADF)	Alternate 24 h fast (~25% of energy) and 24 h feast	Produces large fat loss and insulin-sensitivity gains; may be less tolerable long-term.
Periodic Fasting/FMD	Occasional 3–5 day water/low-calorie “fast”	Induces deep ketosis and metabolic shifts; evidence in T2DM is limited (mostly studied in non-diabetic/pre-DM contexts).

Table 2.

Summary of the positive effects of Intermittent Fasting (IF) on glycaemic control and weight

Study/Regimen	Population (T2DM)	HbA1c Change	Weight Change
5:2 IF + Meal- Replacement (16 wk)	Chinese overweight/obese T2DM, newly diagnosed	HbA1c −1.9% (vs −1.6% metformin, −1.5% empagliflozin)	Weight−9.7 kg (vs −5.5 kg metformin, −5.8 kg empagliflozin)
8 h Time-Restricted Eating (TRE) (24 wk)	US T2D with obesity	HbA1c ~−0.9%, similar to daily calorie restriction	Significant weight loss greater than calorie-counting control
Intermittent (2-day/week) vs. continuous (52 wk)	Australian T2D	Both groups ~−0.5% (IER) vs −0.3% (CER), equivalent	Both groups ~−6.8 kg (IER) vs−5.0 kg (CER) (no significant difference)

In addition, an improvement in insulin sensitivity has been recorded in many studies, and we can expect that IF might also reduce insulin resistance, which is a key factor leading to T2DM.[14,15,16] Such trials showed that IF lowered HbA1c levels, proving that the latter group of followers may be better in terms of long-term glycaemic control. However, we pointed out a theoretical gap: The emerging classification of T2D (e.g., insulin-resistant vs. insulin-deficient subtypes) has not been addressed by any IF trial to date. No evidence currently indicates whether one subtype benefits more from IF than another, and we flagged this as a future research direction.

However, the variability in responses registered among individuals and populations also proved that factors such as age, gender, baseline metabolic status, and compliance to the IF protocols could be the reasons for this outcome.[17] Such differences emphasise the importance of an individual approach to study design and search for specific protocols, which leads to constant efficacy.

Impact on weight management

The scoping review results showed that IF contributed to weight reduction and a positive change in body composition of individuals with T2DM. Vitale and Kim showed that participants who closely adhered to alternate-day fasting and time-restricted eating regimens had reduced body mass compared with those who did not.[18] This weight reduction plays a fundamental role in the process of managing diabetes because of the undeniable link between obesity, especially central obesity, and insulin resistance. Along with an increase in weight loss, IF studies have shown favourable variations in body composition, such as a reduced body fat percentage and increased lean muscle mass.[19] The durability of the effects is notable in these studies, and some instances correspond to a period of time after the end of the intervention during which weight loss is maintained. This indicates that IF could be an alternative strategy to assist weight management in diabetes treatment. However, the review did not find any studies that addressed sarcopenic obesity, particularly in South Asian populations, where the condition is prevalent. This scarcity of evidence indicates a significant research gap in focussed studies that assess IF in sarcopenic patients, particularly in nations such as India.

Challenges with compliance

Although IF has therapeutic advantages for glucose regulation and weight loss, a scoping review suggests that adherence and certain risk factors may be problematic. In other studies, people experienced negative effects through hunger, fatigue, unrest, and sleep disruption, demonstrating that some IF protocols are not easy to follow, especially in the long term.[19,20,21] A specific danger for people with diabetes is that they are prone to low blood sugar, which is particularly the case for people taking medication or insulin. It is well established that IF can precipitate hypoglycaemia in users with insulin or sulfonylurea. Therefore, many trials have excluded such patients or required medication adjustment. For example, one review noted that TRE studies often excluded anyone on insulin or sulfonylureas owing to the higher risk of hypoglycaemia. In practice, if a patient on sulfonylurea or insulin attempts IF, intensive glucose monitoring and dose reduction are needed. Indeed, a clinical trial reduced or stopped sulfonylureas when patients entered fasting (e.g., 50% insulin dose reduction if baseline HbA1c was <7.0%). Therefore, we explicitly state that IF is generally not recommended for those on high-dose sulfonylureas or insulin unless under strict medical supervision.[22,23]

Furthermore, the individual responses among different populations owing to factors such as age, gender, and baseline metabolic health demonstrate that personalised methods of IF can be useful. Such compliance issues would not only necessitate a closer watch but also bring in the need for personalised support for the safe and effective use of IF in diabetes management. Almost all studies were short term (≤6 months). We note that long-term maintenance is largely unstudied in RCT literature. Carter et al.’s[24] study was extended to 12 months (with plans for 24-month follow-up), but published 24-month results are scarce. In general, weight tends to plateau or partially rebound after initial loss. This underscores the need for longer trials to determine whether the benefits of IF are sustainable. Finally, we discuss the practicality differences. Reviews have suggested that TRF regimens (daily shorter fasts) generally have higher adherence than more extreme schedules. Indeed, TRF has been reported to “exhibit a high adherence rate.” In contrast, the 5:2 diet often suffers from low compliance as people tend to overeat on non-fasting days. This informed our recommendation that more “user-friendly” IF patterns (such as TRE) may be the most sustainable.

DISCUSSION

The outcome of this scoping review indicates that IF leads to better blood sugar control in T2DM patients. Blood glucose levels after fasting and increased insulin sensitivity indicate that IF could be a helpful tool for addressing diabetes. This is consistent with the general pattern of diabetes management, in which an increasing number of lifestyle remedies are being acknowledged as valuable cofactors for drug therapy. Many studies have shown that fasting blood sugar levels decrease when participants practice alternate-day fasting and time-restricted meals compared with control groups following conventional eating patterns.[10,15,16,18]

In addition to glycaemic control, this scoping review implies that IF may also help with weight loss and body composition improvement, which are very important for people with diabetes. The primary objective of diabetes treatment is to manage weight, especially central obesity, which is linked to insulin resistance and other metabolic complications.[18] The studies presented in this review demonstrated that IF can cause substantial decreases in body weight, and some of these effects can be sustained over a longer period.[19] This sustainability is impressive as it hints at the possibility that IF is efficient for maintaining weight loss, which is the most common obstacle in obesity and diabetes treatment.

Risk assessment and compliance issues with IF emerged during this review. These risks pose adverse effects such as starvation, exhaustion, and irritability, which in turn make it very difficult for individuals to follow fasting programs.[20] Furthermore, the fact that people respond differently to IF based on age, gender, and the baseline metabolic state in which they exist only makes the picture more complex.[21] This diversity emphasises the need for individualised IF, proper monitoring, and guidance and support for those seeking it as part of their diabetes management plan. Dietary habits, culture, work schedules, and individual preferences must guide the IF design. For instance, qualitative studies have reported that mismatches between prescribed fasting times and a person’s natural eating or work rhythms often lead to poor adherence or even worse outcomes. One participant noted that having to “eat at times that didn’t work with my meds” forced discontinuation of the eating window regimen. Another felt that their metabolism “just did not agree with TRE” and gained weight while fasting. These findings support the recommendation that IF schedules be adapted. For example, aligning the feeding window with the patient’s active hours or habitual meal times can improve sustainability. Furthermore, IF should be implemented alongside culturally appropriate nutritional advice (e.g., choosing healthy local foods and meal patterns) and incremental goal setting for adherence.[25,26,27] This scoping review further emphasises the need for more studies to precisely identify IF methods and long-term effects of IF on diabetes control and weight management. Subsequent research must investigate which IF regimens are most beneficial and evaluate the underlying mechanisms involved in the observed benefits.[21] Also, knowing the psychological and behavioural effects on compliance with IF protocols may also help improve participants’ adherence and make IF interventions effective.

However, inconsistencies exist across studies. For instance, a review conducted by Nowosad and Sujka indicated that some studies showed an increase in fasting glucose, while others showed fasting glucose and insulin reduction simultaneously, affecting the overall goal of weight management and diabetes control.[4] Such inconsistencies might be due to variations in study designs, population diversity, and the protocols used in IF. In addition, some studies are confined to their timeframe, looking at short-term outcomes rather than long-term repercussions, which may not provide a real picture of IF’s sustainability and other effects.

Other variability in the results of other studies is caused by many individual factors, such as age-related declines in metabolic flexibility, hormonal variations in insulin action, and the existence of comorbidities, such as metabolic syndrome, which may augment either the benefit or risk of IF. For example, youngsters with less metabolic impairment may have fewer obvious improvements than older individuals with insulin resistance. Furthermore, a population that is younger and has a more dynamic way of life will respond to IF other than that of the older generation with underlying health disorders.[5] The variability in implementing IF, including the duration and frequency of fasting periods, renders the results even more confusing. These changes indicate that individualised dietary interventions may be essential for maximising the benefits of IF. A few trials have explicitly combined IF with specific diets. We noted that most IF arms simply allowed participants to eat their usual healthy diet within the eating window. Some evidence suggests that pairing IF with a Mediterranean-style diet or other nutritious patterns may optimise the results (one ongoing study, MedDietFast, is testing this), but no completed RCT in our review did so. Therefore, we added that cultural dietary habits and quality (e.g., Mediterranean, ketogenic) could influence outcomes, but this remains untested in T2DM RCTs under the eligibility criteria. As a result, it is imperative to conduct in-depth studies that run over a longer period and examine a wider spectrum of factors. This may help patients better understand the possible risks and benefits of IF, making the role of IF in diabetes care and weight management clearer.

Moreover, IF should be carefully considered for patients with chronic comorbidities that can affect the outcomes of IF, including those with comorbid diabetes. These adverse effects could include hypoglycaemia and dizziness, as well as aggravation of disordered eating disorders. Hence, medical guidance is vital for people with co-morbidities contemplating this diet. Adherence to IF could be another problem; some people may become worried or irritable or have disrupted sleep.[7] The strict timetables of some IF rules do not match those of people with busy or unpredictable routines and may create hunger or social disconnection. This will likely detract from the long-term advantages of IF and may even make it difficult to adhere to the diet.

In addition to social and cultural factors, the feasibility of IF also involves other factors. We have expanded the discussion on inter-individual heterogeneity. In particular, genetic, metabolic, and lifestyle factors can modulate IF responses. For example, inter-individual differences in insulin resistance, β-cell function, and visceral adiposity may influence glycaemic outcomes. Even meal composition, timing, and ethnicity affect post-meal glucose responses, and emerging data have linked gut microbiome profiles to differing IF benefits. These sources of variability (e.g., differing baseline HbA1c or fat distribution, men vs. women, young vs. old) likely explain why some patients see large improvements, while others see minimal change.[25,26] The literature notes that factors such as carbohydrate amount, glycaemic index of meals, meal timing relative to circadian rhythms, and ethnic/genetic background all contribute to the observed differences in glucose and weight outcomes. By elucidating these biological and behavioural moderators, we can better interpret the mixed results and identify the subgroups most likely to benefit from IF.[25,26] Fasting can also affect family meals, social events, and food-related customs. Thus, disruption can be a source of social tension or even impede participation in traditional social activities, making it difficult to observe IF. We noted that no eligible RCTs focussed exclusively on Indian or Southeast Asian cohorts between 2019 and 2024. Our review included mainly Western and Chinese studies. The largest Asia-based trial (China) showed robust benefits of a 5:2 IF regimen; however, specific data on South Asian (Indian) phenotypes are lacking. Given that Asian patients often develop diabetes at a lower BMI and with greater central fat, IF’s effects could differ in this group. However, this remains to be tested. Thus, we acknowledge a gap in the evidence regarding Indian/South-Asian populations.[27] For IF to be secure and suitable for different groups of people, it is necessary to assess its possible risks and contraindications, matching the approach to each person’s specific requirements and situations.

In real life, IF may be an effective option for T2DM management and weight control. Nevertheless, health professionals should be careful while prescribing IF, thoroughly informing patients about possible dangers, and offering the necessary support. Teaming dietitians, endocrinologists, and other healthcare professionals will ensure that patients receive thorough evaluations and supportive guidance when considering IF. Generally, IF by itself primarily induces fat loss. Gains in muscle would require added resistance training, which was not implemented in the trials we reviewed.[25,26] By design, we included only T2DM patients. Consequently, none of the reviewed studies enrolled obese participants without dysglycaemia. Therefore, we cannot directly compare weight loss in non-diabetic and diabetic subjects within our scope.

Diabetes management encompasses a diverse range of options including medication, lifestyle, and nutritional adjustments. This underscores the significance of an all-encompassing method combining therapy with lifestyle transformation and diet implementation, such as IF. Through IF, there have been evident improvements in blood glucose levels, insulin sensitivity, and weight management, among others, thus offering a supplementary or alternative to drug interventions.

These findings imply that IF may be beneficial for T2DM patients to achieve better glycaemic control and assist in weight management. However, we clarified that almost no study has combined IF with a structured exercise program. Any reported changes in body composition should be interpreted with caution. For example, the TRE versus calorie-restricted trial did not include prescribed exercise and found weight and HbA1c improvements but only stable or slightly decreased lean mass. Nevertheless, future work may focus on unraveling the best IF protocols, revealing predictors of therapeutic response, examining long-term effects, and addressing safety and compliance concerns.[21] By knowing the variety of responses and using personalised tactics in clinical practice can increase the effectiveness of IF, thereby improving the health outcomes of individuals with T2DM. Additionally, future research should include psychological and behavioural aspects to improve compliance with IF. Healthcare workers should consider these factors when recommending IF; that is, patients should receive support and monitoring, along with successful diabetes management and weight control.

CONCLUSIONS

This scoping review suggests that IF is an efficient method to manage diabetes and weight loss. IF protocols, such as intermittent and alternate-day fasting, can reduce fasting blood sugar levels and improve the insulin response. These findings suggest that it is possible to control diabetes. Moreover, IF positively affected weight loss with evidence of long-term sustainability. However, the scoping review recommended possible risks and difficulties in compliance. Individual reactions to IF include both benefits and risks such as hunger, irritability, and deleterious effects on people with chronic diseases. Such difficulties require a thoughtful, individualised regime and expert medical advice to implement IF. In light of the various outcomes, more research is required to find the best available IF protocols and determine the long-term consequences of controlling diabetes and weight management. The need for RCTs that directly compare popular methods in the same population to identify the most effective and sustainable strategy are also required.

Author contributions

Study concept and design: MM; acquisition of data: THK and XBL; analysis and interpretation of data: MM, THK, and XBL; drafting of the manuscript: THK; critical revision of the manuscript: MM; statistical analysis: MM and THK; obtained funding: N/A; administrative, technical, or material support: XBL; and study supervision: MM.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence

Artificial intelligence was not used in any form for analysis or writing of this research article.

Funding Statement

Nil.