Table 1.

Synthesis of results.

Study [Ref]	Level of Evidence	Population	Protocol	Energy Balance	Metabolic Effect	Other Results
R1 Antoni et al. 2018 [27]	Low	n = 13 Healthy adults, 29–57 years.	↓ Food window of 3 h 10-week non-randomized controlled trial.	↓ daily energy intake	↓ body 1.9% fat mass index ↓ fasting blood glucose	Only 19% withdrawal including one lost to follow-up
R2 Jamshed et al. 2019 [28]	Medium	n = 11 Healthy adults, 32 ± 7 years.	Early TRE 6/18 4-day randomized controlled iso-caloric crossover trial with 3.5 to 5 weeks of wash-out	No difference in calorie intake (iso-caloric)	↓ 24-h glucose and hyperglycemic excursion ↓ insulin resistance ↑ total cholesterol, LDLc, HDLc	↑ BDNF ↓ IGF1 Modification of genes expressions involved in circadian rhythm, longevity, autophagy
R3 Smith et al. 2017 [29]	Low	n = 20 Healthy women, 21.3 ± 1.2 years.	Delayed TRE 8/16 4-week single-arm trial		↓ body mass of 0.6 ± 1 kg ↓ body fat in participants that strength trained (>3 day/week)
R4 Sutton et al. 2018 [30]	Medium	n = 8 Pre-diabetic overweighted men, 59 ± 9 years.	Early TRE 6/18 5-week controlled, randomized, isocaloric crossover trial with 7 weeks of wash-out	No difference in calorie intake (iso-caloric)	↓ insulin (fasting, mean and peak) ↑ insulin sensitivity ↓ insulin resistance ↑ triglycerides ↓ blood pressure	↓ desire to eat ↓ 8-isoprostane
R5 Ravussin et al. 2019 [31]	Medium	n = 11 Healthy adults, 32 years.	Early TRE 6/18 4-day controlled, randomized, iso-caloric crossover trial with 3.5 to 5 weeks of wash-out	No difference in calorie intake (standardized meals) Energy expenditure unchanged		↓ several aspects of hunger ↓ in morning ghrelin, leptin and GLP-1 ↓ average ghrelin ↑ in evening PYY (satiety)
R6 Gabel et al. 2019 [32]	Low	n = 23 Obese, 50 ± 2 years.	TRE 8/16 12-week single-arm trial.	Physical activity unchanged. No measure of calorie intake	↓ 4% weight ↓ 5% fat mass	80% mean adherence.
R7 and 9 Gabel et al. 2018, 2014 [33,34]	Low	n = 23 Obese, 50 ± 2 years.	Delayed TRE 8/16 12-week, non-randomized controlled trial with matched historical group.	↓ of 350 kcal/day Physical activity unchanged.	↓ 2.6% of relative weight ↓ of relative BMI ↓ systolic blood pressure of 7 ± 2 mmHg	74% adherence rate. No one in the TRE group reported dropping out due to issues with the diet.
R8 Moro et al. 2016 [35]	Medium	n = 34 Adults who strength train, 29.21 ± 3.8 years.	TRE 8/16 + RT 8-week randomized controlled trial. TRE + RT vs. RT	No difference in calorie intake between groups No difference in physical activity during training sessions	↓ fat mass ↓ blood glucose levels ↓ insulin resistance ↓ triglycerides	↓ TNF-α ↓ IL-1 β ↓ IGF 1 ↑ adiponectin ↓ respiratory ratio (lipid oxidation) Conservation of muscular mass and strength
R10 Anton et al. 2019 [36]	Low	n = 10 Overweighted elderly adults, 77.1 years.	TRE 8/16 4-week single-arm trial.		Mean weight ↓ of 2.6 kg	↑ walking speed Improvement in mental and physical function. 84% mean adherence.
R11 Hutchison et al. 2019 [37]	Medium	n = 15 Pre-diabetic men, 55 ± 3 years.	dTRE 9/15 vs. eTRE 1-week cross-over, randomized trial with 2 weeks of wash-out	No difference in physical activity No measure of calorie intake	↓ glucose AUC and mean fasting glucose in eTRE ↓ triglycerides in two groups	No effect of TRF on perceived hunger, fullness, or desire to eat.
R12 Tinsley et al. 2016 [38]	Medium	n = 18 Adults who strength-train, 22 ± 2.4 years.	TRE 4/20 + RT vs. RT alone. 8-week randomized controlled trial.	↓ of 650 kcal/day between fasting days and non-fasting days ↓ weekly calorie intake	No significant change in weight and fat mass	Conservation of lean mass, muscular volume and muscular strength. 95% mean adherence.
R13 Gasmi et al. 2017 [39]	Medium	n = 40 20 y (n = 40) vs. 50 years (n = 20)	TRE 12/12: TRE 50 years + 20 years Control 50 years + 20 years 12-week randomized, controlled trial.	No difference in calorie intake.	No change in body composition and muscular function	↓ immuno-senescence
R14 Tinsley et al. 2019 [40]	Medium	n = 40 Women who strength-train 18–30 years.	Delayed TRE 8/16 8-week randomized controlled trial. -RT + placebo -TRE + RT + placebo -TRE + RT + HMB	↑ calorie intake from 20 to 200 kcal/day No difference in physical activity and REE	↓ fat mass of 4%–7% in per protocol analysis for the 2 TRE groups	No side effects in 90% of participants at the end of the protocol
R15 Gill et al. 2015 [41]	Low	n= 8 Obese adults, 18 years.	TRE 10/14 every day, 3-week single-arm trial. Smartphone-based assessment of caloric quantity and timing intake	↓ calorie intake of 20%	↓ weight by 4% ↓ BMI by 1.15 kg/m2	↑ sleep quality ↓ hunger
R16 Lee et al. 2020 [42]	Low	n = 10 Overweight sedentary elderly adults, 77.1 years.	TRE 8/16 every day with self-selection of eating window. 4-week single-arm trial.			Mean adherence of 84%.
R17 Kesztyüs et al. 2019 [43]	Low	n = 40 Abdominally obese, 49.1 ± 12.4 years.	TRE 8/16 every day with self-selection of the food intake period 12-week single-arm trial.		↓ weight of 1.7 ± 2.5 kg ↓ BMI of 0.6 ± 0.9 kg/m2 ↓ WC −5.3 ± 3.2 cm ↓ HbAc1 by 1.4 ± 3.5 mmol/mol	Mean adherence of 86 ± 15%
R18 Wilkinson et al. 2020 [44]	Low	n = 19 Adults with MetS 59 ± 11 years.	TRE 10/14 every day with self-selection of the food intake period. 12-week single-arm trial.	↓ by 8.62% ± 14.47%. No difference in physical activity.	↓ body weight (−3%) ↓ BMI (−3%) ↓ body fat (−3%) ↓ visceral fat rating (−3%) ↓ WC-4.46 ± 6.72 cm ↓ total cholesterol ↓ LDLc, ↓ non-HDLc ↓ systolic and diastolic BP	Mean adherence of 85 ± 12%. 63.2% participants were somehow engaged in TRE at 16 ± 4 months. ↑ in sleep duration by 12.45 min. ↑ in sleep duration and efficiency in 84% of participants.
R19 McAllister et al. 2019 [45]	Medium	n = 22 Physically active men, 22 ± 2.5 years.	TRE 8/16 every day ad libitum vs. Isocaloric (↓ 300 kcal from baseline). 4-week randomized controlled trial.	No difference in calorie intake	↓ body mass in both groups ↓ body fat mass in both groups ↓ systolic BP in both groups ↑ HDLc in both groups	↑ adiponectin in both groups. Improvement in subjective outcomes (alertness, energy, focus, mood) in ad libitum.
R20 Chow et al. 2020 [46]	Low	n = 20 Overweight adults with prolonged eating window (15.4 ± 0.9 h/day). 45.5 ± 12 years.	TRE 8/16 ad libitum every day. 12-week controlled non-randomized trial. TRE 8/16 group vs. non-TRE group.	No difference in physical activity. No measure of calorie intake.	(1) vs. non-TRE group ↓ body weight ↓ lean mass ↓ visceral fat (2) vs. preintervention measures ↓ body weight ↓ fat mass ↓ lean mass ↓ visceral fat	↓ of eating window in TRE group (9.9 ± 2 h) compared with non-TRE group. Adherence in TRE: 83.1% Correlation between restriction of eating window with fat and visceral masses loss
R21 Parr et al. 2020 [47]	Medium	n = 11 Overweight/obese and sedentary men. 38 ± 5 years.	TRE 8/16 every day vs. non-TRE (15 h/day). 5-day randomized crossover trial with a 10-day wash out period.	No difference in calorie intake (iso-caloric). No difference in physical activity.	↓ nocturnal glucose AUC TRE group ↓ peak insulin concentrations at breakfast in TRE group ↓ peak glucose concentration at breakfast in TRE group	100% adherence. Improvement of subjective feelings (well-being and satisfaction) ↓ evening hunger in TRE group
R22 Parr et al. 2020 [48]	Low	n = 19 Obese adults with T2D. 50 ± 9 years.	TRE 9/15 every day. 4-week singe-arm non-randomized trial	No difference in calorie intake. Adherence to TRE reduces calorie intake.	NS.	Mean compliance of 72 ± 24% (≅5 days/week).
R23 Miguet et al. 2020 [49]	High	n = 105 Overweight and obese adults. 46.5 ± 10.5 years.	dTRE 8/16 every day. 12-week controlled randomized trial. TRE 8/16 vs. control group.	No difference in calorie intake. No measure of physical activity.	↓ body weight in TRE group (1.17%) compared to baseline that was not significantly different from control group (0.75%).

☒: No measurement. NS: non-significant modification (p > 0.05). Abbreviations: AUC: area under the curve; BDNF: brain-derived neurotrophic factor; BP: blood pressure; HDLc: HDL cholesterol; HMB: hydroxy-methyl-butyrate supplementation; IL: interleukin; insulin R: insulin resistance; insulin-S: insulin sensitivity; LDLc: LDL cholesterol; MetS: metabolic syndrome; REE: resting energy expenditure; RT: resistance training; T2D: type 2 diabetes; WC: waist circumference.