Table 1.

Characterization of the studies included in the quantitative analysis synthesis.

	Study Type	Control Conditions	Experimental Conditions	IF Protocol	Duration (Days)	Age (Mean ± SD)	Participants (n and Gender)	Results Overview
1. Guo I, et al., 2021 [32]	RCT	MetS	MetS	ADF 5 + 2 (NC)	56	CTL = 42.7 ± 4.1 EG = 36.6 ± 5.7	CTL—11 M/7 W EG—10 M/12 W	Weight, waist circumference, BMI, triglycerides, insulin resistance and fasting insulin were significantly improved after IF. CTL comprises individuals with MetS maintained their habitual diet and lifestyle.
2. Parvaresh A, et al., 2019 [47]	RCT	-	MetS	ADF 4 + 3 (NC)	56	EG = 44.6 ± 9.8	EG—21 M/14 W	mADF diet is an effective option for managing body weight, waist circumference, systolic blood pressure and fasting plasma glucose when compared with common calorie restriction. CTL comprises individuals with MetS that consumed 75% of their energy needs each day.
3. Gabel K, et al., 2019 [29]	RCT	-	Obesity	ADF 1 + 1 (NC)	365	CTL = 43 ± 1 EG = 43 ± 3	CTL—4 M/11 W EG—9 M/2 W	ADF may produce greater reductions in fasting insulin and insulin resistance compared with caloric restriction in insulin-resistant participants despite similar decreases in body weight. CTL comprises obese individuals that maintained their usual eating and activity habits.
4. Cho A-Ra, et al., 2019 [23]	RCT	-	Overweight	ADF 4 + 3 (NC)	56	CTL = 42.6 ± 10.6 EG = 33.5 ± 5	CTL—3 M/2 W EG—3 M/6 W	Exercise, with or without ADF, improves cholesterol metabolism (serum sterol signatures) and increased physical activity has a greater effect on cholesterol biosynthesis than weight reduction or calorie restriction. CTL comprises overweight individuals that maintained their usual eating and activity habits.
5. Corley BT, et al., 2018 [9]	RCT	-	T2D	ADF 5 + 2 (C) 5 + 2 (NC)	84	62 (44 to 77) * 58 (42 to 74) *	11 M/7 W 11 M/8 W	IF in a 5 + 2 protocol (both consecutive and non-consecutive) increases the rate of hypoglycaemia in patients with T2D, even after education on this topic and medication adjustments. Yet it improves weight, HbA1c, fasting glucose and quality of life (both protocols).
6. Hutchison AT, et al., 2018 [34]	RCT	Overweight or Obesity	Overweight or Obesity	ADF 4 + 3 (NC)	70	CTL 1 = 49 ± 3 CTL 2 = 49 ± 2 EG-IF100 = 51 ± 2 EG-IF70 = 51 ± 2	CTL 1—11 W CTL 2—11 W EG-IF100—22 W EG-IF70—22 W	IF combined with a 30% caloric restriction is better at improving weight, fat mass, HOMA-IR, fasting glucose, non-esterified fatty acids, total cholesterol, LDL-cholesterol and triglycerides than energy-matched continuous caloric restriction. CTL comprises overweight or obese women maintained under continuous food intake at 100% of baseline energy requirements.
7. Sundfør TM, et al., 2018 [54]	RCT	-	Overweight and MetS	ADF 5 + 2 (NC)	365	EG = 49.9 ± 10.1	EG—28 M/26 W	Both intermittent and continuous energy restriction promoted similar weight loss, maintenance and improvement in cardiovascular risk factors after one year. However, the feelings of hunger, appears to be more pronounced during IF.
8. Trepanowski JF, et al., 2018 [61]	RCT	-	Obesity	ADF 1 + 1 (NC)	168	CTL = 44 ± 2 EG = 46 ± 2	CTL—4 M/21 W EG—3 M/22 W	ADF and CR similarly increased the fat-free mass:total-mass ratio, decreased circulating leptin and did not affect the visceral adipose tissue:subcutaneous adipose tissue ratio or other measured adipokines. Weight loss, rather than the pattern of energy restriction, appeared to be the main driver of these changes. CTL comprises obese individuals that maintained their usual diet.
9. Conley M, et al., 2018 [25]	RCT	-	Obesity	ADF 5 + 2 (NC)	180	EG = 68 ± 2.7	EG—11 M	The 5:2 diet is a feasible weight loss strategy in this older male population. Furthermore, it also indicates that participants were able to follow the diet sufficiently to induce magnitudes of weight loss similar to that of standard dietary modification practices, and the diet did not appear to cause an unbalanced nutritional intake.
10. Li C, et al., 2017 [43]	RCT	T2D	T2D	ADF 1 week fasting	7	CTL = 64.4 ± 5.7 EG = 64.7 ± 7	CTL—16 NS EG—16 NS	A 1-week fasting therapy is promising for the improvement of weight, waist circumference, SBP, DBP and HOMA-IR in T2D patients, when compared with typical T2D medication. CTL comprises T2D individuals that followed the principles of a Mediterranean diet.
11. Catenacci VA et al., 2016 [22]	RCT	-	Obesity	ADF 1 + 1 (NC)	56	EG = 39.6 ± 9.5	EG—3 M/10 W	ADF is a safe and tolerable approach for weight loss, it improved weight, body composition, lipids and insulin sensitivity index at 8 weeks while not increasing the risk for weight regain up-to 24 weeks after completing the intervention.
12. Hoddy KK, et al., 2014 [33]	RCT	-	Obesity	ADF 1 + 1 (NC)	70	ADF-L: 45 ± 3 ADF-D: 45 ± 3 ADF-SM: 46 ± 2	ADF-L: 3 M/17 W ADF-D: 4 M/15 W ADF-SM: 2 M/18 W	This study demonstrated there is flexibility in the timing of the fast day meal during ADF. People with obesity may feed at dinner or as small meals throughout the day, and experience similar weight loss, body composition and cardiovascular benefits as the traditional lunch time approach.
13.Varady KA et al., 2009 [55]	CRS	-	Obesity	ADF 1 + 1 (NC)	56	EG = 46 ± 2.4	EG—4 M/12 W	ADF is a viable diet option to help obese individuals lose weight and decrease coronary artery disease risk.
1. Kotarsky CJ, et al., 2021 [41]	RCT	Overweight or Obesity	Overweight or Obesity	TRF 16 + 8	56	CTL = 44 ± 2 EG = 45 ± 3	CTL—9 M/1 W EG—9 M/2 W	IF associated with exercise training is a short-term dietary strategy for reducing fat mass and increasing lean mass in overweight and obese adults. CTL comprises overweight or obese individuals that maintained their usual diet.
2. de Oliveira Maranhao Pureza IR, et al., 2021 [26]	RCT	Overweight or Obesity	Overweight or Obesity	TRF 12 + 12	365	19–44	EG –31 W	IF may help in the long-term management of obesity.
3. Kunduraci YE, et al., 2020 [7]	RCT	MetS	MetS	TRF 16 + 8	84	EG = 47.44 ± 2.17	EG—16 M/16 W	Weight, BMI, total cholesterol, LDL, triglycerides, fasting glucose, systolic and diastolic blood pressure, insulin resistance and fasting insulin were significantly improved after IF.
4. Cienfuegos S, et al., 2020 [24]	RCT	-	Obesity	TRF 20 + 4 18 + 6	56	4 h_TRF: 49 ± 2 6 h_TRF: 46 ± 3	4 h_TRF: 2 M/14 W 6 h_TRF: 1 M/18 W	4- and 6-h TRF regimens lead to similar weight loss over the 2 months in peolple with obesity while also decreasing insulin resistance and oxidative stress. CTL comprises obese individuals that maintained their usual diet.
5. Jones R, et al., 2020 [35]	CCS	Healthy	Healthy	TRF 16 + 8	14	CTL = 23 ± 1 EG = 23 ± 1	CTL—8 M EG—8 M	Weight showed significant improvement after IF. CTL comprises healthy individuals following a dietary plan provided with all food and beverages that matched the macronutrient composition (45% CHO, 35% fat and 20% protein).
6. Zhao L, et al., 2022 [58]	CRS		Overweight	TRF 14 + 10	56	63 ± 4	15 M	This study demostrated that TRF had a net effect of reducing glycemia and dampening energy-consuming pathways in adipose tissue.
7. Parr EB, et al., 2020 [46]	CRS	T2D	T2D	TRF 15 + 9	28	50.2 ± 8.9	9 M/10 W	Fasting insulin showed significant improvements after IF.
8. Gabel K, et al., 2020 [30]	CRS	-	Obesity	TRF 16 + 8	84	-	14 M	This study suggest that the mild weight loss (2%) induced by time restricted eating did not significantly alter the diversity or overall composition of the gut microbiome.
9. Wilkinson MJ, et al., 2020 [56]	CRS	-	MetS	TRF 14 + 10	84	59 ± 11.4	15 M/6 W	TRF mproved cardiometabolic health of patients with metabolic syndrome receiving standard medical care including high rates of statin and anti-hypertensive use.
10. Anton SD, et al., 2019 [19]	CRS	-	Overweight	TRF 16 + 8	21	77.1	4 M/6 W	TRF is an acceptable and feasible eating pattern for overweight, older adults to follow while also promoting short-term weight loss.
11. Kesztyüs D, et al., 2019 [38]	CRS	-	MetS	TRF 16 + 8	90	49.1± 12,4	9 M/31 W	TRE may help to reduce abdominal obesity and hence prevent cardio-metabolic diseases.
12. Arnason FB, et al., 2017 [20]	CRS	-	T2D	TRF 18–20 h fasting per day	14	53.8 ± 9.11	1 M/9 W	Weight and BMI were improved after IF.
13. Schroder JD, et al., 2021 [51]	NRCT	Obesity	Obesity	TRF 16 + 8	90	CTL = 42.3 ± 3.5 EG = 36.6 ± 1.6	CTL—12 W EG—20 W	Weight, waist circumference, BMI, SBP and DBP were improved after IF. CTL comprises obese individuals that maintained their usual diet.
1. Zouhal H, et al., 2020 [59]	RCT	-	Obesity	RF Ramadan	30	CTL = 23.8 ± 3.8 EG = 24 ± 3.4	CTL—14 M EG—14 M	Ramadan fasting improves systemic inflammation biomarkers in males with obesity. CTL comprises obese individuals that did not fast during Ramadan.
2. Zouhal H, et al., 2020 [60]	RCT	-	Obesity	RF Ramadan	30	CTL = 23.8 ± 3.7 EG = 24.5 ± 3.8	CTL—15 M EG—15 M	IF during Ramadan is an effective strategy to modify appetite-regulating hormones, leading to improved body composition indices and reduced obesity.
3. Abdullah K, et al., 2020 [18]	CS	Healthy	Healthy or T2D	RF Ramadan	30	CTL = 34.61 ± 4.31 EG = 34.35 ± 3.83 EG = 50.17 ± 12.95	CTL—31 M EG—37 M EG—30 M	This study compares the effect of IF in patients with T2D, their first-degree relatives and healthy individuals. Leptin, adiponectin, leptin:adiponectin ratio, HOMA-beta and HbA1c were significantly improved in all groups. Fasting blood glucose and growth hormone levels were improved in control and first-degree relatives. C-peptide, HOMA-IR, HOMA-S and insulin levels were improved in T2D patients and first-degree relatives. CTL comprises healthy control with fasting blood glucose <100 mg/dL.
4. Yeoh ECK, et al., 2015 [57]	CS		T2D	RF Ramadan	30	57 ± 11	15 M/14 W	Ramadan fasting can be practiced safely with prior patient education and medication adjustment with modest benefits on metabolic profile and body composition, particularly among females.
5. Feizollahzadeh S, et al., 2014 [28]	CS	-	Healthy with Overweight	RF Ramadan	30	47.88	70 M	Weight and BMI were improved after IF although total cholesterol, triglycerides and fasting glucose levels were also increased.
6. Karatoprak C, et al., 2013 [37]	CS		T2D	RF Ramadan	30	57.4 ± 10.1	19 M/57 W	Results showed no negative effects of extended fasting on glucose regulation in diabetic patients using certain medications.
7. McNeil J, et al., 2014 [45]	CCS	Healthy	Obesity	RF Ramadan	14	27 ± 4.5	10 M	Data demostrated significant increased of glucose, total cholesterol and LDL-C levels during Ramadan fast in normal-weight and obese men. Dietary restraint scores were also greater during Ramadan. Lastly, changes in anthropometric parameters were related to changes in metabolic profiles, dietary restraint and disinhibition eating behavior trait scores.
8. Kovil R, et al., 2020 [42]	CRS	-	T2D	RF Ramadan	30	21–80 **	25 M/25 W	This study did not show any significant changes in the parameters evaluated after IF.
9. Faris E, et al., 2019 [27]	CRS	-	Overweight or Obesity	RF Ramadan	30	36.2 ± 12.5	35 M/22 W	Weight, BMI, total cholesterol, triglycerides and SBP were improved after IF although HDL was also decreased.
10. Madkour MI, et al., 2019 [44]	CRS	-	Healthy or Obesity	RF Ramadan	30	CTL = 29.8 ± 14 EG = 35.72 ± 12.35	CTL—6 EG—34 M/22 W	Fasting glucose, insulin, insulin resistance expressed in homeostatic model assessment (HOMA-IR) remained unchanged throughout the study, while significant (p < 0.05) decreases in total cholesterol, triglycerides and HDL cholesterol were observed.
11. Abdessadek M, et al., 2019 [17]	CRS	-	T2D	RF Ramadan	30	-	57 M/93 W	This study showed a significant decrease in glycemic parameters (glycated haemoglobin and fasting blood glucose), and also significant variations in lipid profile before and after Ramadan, respectively. Furthermore, it also demostrated that in well-controlled T2D patients under antidiabetic drugs, the risk of hypoglycaemia is very low and patients may fast safely in Ramadan.
12. Prasetya G, et al., 2018 [48]	CRS	-	Healthy	RF Ramadan	29	24.3 ± 3.7	27 M	Weight, waist circumference, BMI, insulin resistance and fasting insulin were improved after IF although HDL levels were also decreased.
13. Kamble S, et al., 2018 [36]	CRS	-	Healthy	RF Ramadan	39	20–35 **	30 (NS)	No changes after IF.
14. Sezen Y, et al., 2016 [52]	CRS	-	Obesity	RF Ramadan	30	37 ± 7	70 M	Ramadan fasting was beneficial for body composition, but had no effect on arterial stiffness and resting heart rate.
15. Gnanou JV, et al., 2015 [31]	CRS	-	Healthy	RF Ramadan	39	19–23 **	20 M	Weight, BMI, fasting glucose, fasting insulin and insulin resistance were improved after IF.
16. Sahin SB, et al., 2013 [49]	CRS	-	T2D	RF Ramadan	30	56.93 ± 9.57	40 M/82 W	Fasting during Ramadan did not worsen the glycemic control of T2D patients.
17. Shariatpanahi MV, et al., 2012 [53]	CRS	-	MetS	RF Ramadan	30	40.14 ± 10.8	65 M	Change in the number and timing of meals and portioning of the daily energy consumption decreases inflammatory markers in MetS.
18. Salehi M and Neghab M, 2007 [50]	CRS	-	Obesity	RF Ramadan	29	23.4 ± 1.3	28 M	Consumption of a medium calorie balanced diet in conjunction with sufficient fluid intake during Ramadan and fasting may significantly decrease serum levels of glucose, cholesterol, as well as weight and BMI.
19. Khaled MB, et al., 2006 [39]	CRS	-	Obesity	RF Ramadan	29	23.4 ± 1.3	60 W	Beneficial effect of Ramadan fasting on glucose homeostasis, and an unbalanced profile on lipids.
20. Khatib FA and Shafagoj YA, 2004 [40]	CRS	-	T2D/Obesity	RF Ramadan	29	51 ± 10	44 M	Non-insulin dependent T2D patients displayed a trend towards better glycemic control following Ramadan fasting.
21. Bener A, et al., 2018 [21]	CSS		T2D	RF Ramadan	30	55.39 ± 15.3	593 M/653 W	Ramadan fasting has positive effects on T2D patients by decreasing blood pressure, blood glucose and HbA1C levels and BMI. It also improved sleep duration and physical activity.
TOTAL							1551 M/1491 W/ 68 NS

RCT—Randomized controlled trial; CS—Cohort study; CRS—Case report series; NRCT—non-randomized controlled trial; CSS—Cross-sectional study; MetS—Metabolic syndrome; T2D—diabetes mellitus type 2; C—consecutive; NC—Non-consecutive; CTL—Control; EG—Experimental Group; NS—Not specified; ADF—alternate-day eating; CR—caloric restriction; TRF—Time-restrict eating; IF70—Intermittent fasting 70%; IF100—Intermittent fasting 100%; M—Men; W—Women; HOMA-IR—insulin resistance; BMI—Body mass index; SBP—Systolic blood pressure; DBP—Diastolic blood pressure; * mean (range); ** range.