Intermittent fasting and weight loss: Systematic review

Stephanie Welton; Robert Minty; Teresa O’Driscoll; Hannah Willms; Denise Poirier; Sharen Madden; Len Kelly

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Table 1.

Summary of IF studies: Total IF participants = 944.

STUDY, Y	N	POPULATION^*	LEVEL OF EVIDENCE	DURATION	WEIGHT LOSS, % OF BASELINE WEIGHT	INTERVENTION^†	KEY RESULT
Anton et al,¹⁰ 2019	10	Obese, > 65 y	II	4 wk	2.2	16-h daily fast; self-reported	IF is feasible in older adults and leads to weight loss
Antoni et al,¹¹ 2018	41	Overweight and obese	I	Until 5% weight loss is reached	5.3	2-d fast (25% of caloric needs) and 5-d ad libitum calorie intake vs CR; self-reported	59 d to achieve 5% weight loss with IF; not statistically different in CR group (73 d)
Arnason et al,¹² 2017	10	Obese, T2D	II	2 wk	1.4	18- to 20-h daily fast as a goal, but average fast was 16.8 h; 2-wk follow-up; self-reported	Short-term IF might be safe in patients with T2D and might improve glycemic control
Bhutani et al,¹³ 2013 Bhutani et al,¹⁴ 2013	64	Obese	I	12 wk	3.2	Alternated 25% of caloric needs with ad libitum calorie intake vs usual diet with or without exercise; self-reported	IF in combination with exercise is more effective than either method alone
Bowen et al,¹⁵ 2018	136	Overweight and obese	I	16 wk	10.6	3-d fast, 3-d CR, and 1-d ad libitum intake vs CR; 8-wk maintenance; self-reported	CR combined with IF does not improve on weight loss of CR alone
Carter et al,¹⁶ 2016	51	Obese, T2D	I	12 wk	5.9	2-d fast (1670 to 2500 kJ/d) and 5-d usual diet vs CR; self-reported	IF is a viable alternative to CR for weight loss and glycemic control in T2D
Carter et al,¹⁷ 2018 Carter et al,¹⁸ 2019	137	Obese, T2D	I	52 wk	6.8	2-d fast (25% of usual calorie intake) and 5-d usual diet vs CR; 1-y follow-up; self-reported	Similar decrease in HbA_1c level and weight with IF or CR; weight is stable and HbA_1c level climbs in follow-up
Catenacci et al,¹⁹ 2016	26	Obese	I	8 wk	8.7	Alternated 0% usual calorie intake with ad libitum intake vs CR; 24-wk follow-up; monitored	IF is a safe weight-loss strategy; no increase in risk of weight regain
Cho et al,²⁰ 2019	31	Overweight and obese	I	8 wk	5.0	Alternated 25% usual calorie intake with ad libitum intake vs usual diet with or without exercise; self-reported	Exercise does not improve weight loss for IF alone
Corley et al,²¹ 2018	41	Obese, T2D	II	12 wk	0.8	2-d fast (2 small snacks, 1 light meal) and 5-d ad libitum intake; self-reported	IF safe in T2D; promotes weight loss and glycemic control
Coutinho et al,²² 2018	35	Obese	I	12 wk	13.0	3-d fast (25% of caloric needs) and 4-d full caloric needs vs CR; self-reported	Similar weight losses result from IF and CR
Eshghinia and Gapparov,²³ 2011	26	Obese women	II	4 wk	4.9	3-d fast (25% to 40% of usual caloric intake) and 4-d CR (10% decrease in usual caloric intake) per wk; self-reported	Short-term IF with CR is a viable weight-loss strategy in obesity
Eshghinia and Mohammadzadeh,²⁴ 2013	15	Obese women	II	6 wk	7.1	3-d fast (25% to 30% of caloric needs), 3-d usual diet, and 1-d ad libitum intake; self-reported	Short-term IF is a viable weight loss strategy in obesity
Gabel et al,²⁵ 2018 Gabel et al,²⁶ 2019	46	Obese	I	12 wk	3.2	16-h fast daily vs usual-diet historical controls; self-reported	IF leads to weight loss compared with baseline and control group
Harvie et al,²⁷ 2011	107	Obese women	I	24 wk	7.9	2-d fast (very low-calorie intake) and 5-d usual diet vs CR; self-reported	IF is as effective as CR for weight loss and insulin sensitivity
Headland et al,²⁸ 2019	244	Obese	I	52 wk	5.6	2-d fast (25% of usual calorie intake) and 5-d usual diet vs CR; self-reported	IF and CR have similar weight loss results at 1 y
Hoddy et al,²⁹ 2014 Hoddy et al,³⁰ 2015 Hoddy et al,³¹ 2016 Hoddy et al,³² 2016	59	Obese	I	8 wk	4.2	Alternated daily 25% of baseline caloric needs with ad libitum caloric intake; self-reported	IF is a safe weight-loss strategy; no increased risk of disordered eating; might decrease insulin resistance
Hutchison et al,³³ 2019	88	Overweight and obese women	I	8 wk	4.6	3-d fast (32%–37% of energy requirements) and 4 d at 100% or 145% of energy requirements vs CR and control group; self-reported	Combining CR and IF is more effective for weight loss than either alone
Kahleova et al,³⁴ 2014	54	Obese, T2D	I	12 wk	3.9	16-h daily fast vs CR; self-reported	IF is more effective than CR for weight loss and glycemic control in T2D
Klempel et al,³⁵ 2012 Kroeger et al,³⁶ 2012	54	Obese women	II	8 wk	3.4	1-d fast (very low-calorie intake) and 6-d CR; self-reported	IF combined with CR promotes weight loss in obese women
Klempel et al,³⁷ 2013 Klempel et al,³⁸ 2013 Klempel et al,³⁹ 2013 Varady et al,⁴⁰ 2015	32	Obese women	II	8 wk	4.5	Alternated 25% of usual calorie intake with 125% of usual calorie intake; high-fat vs low-fat diet; self-reported	IF is effective for weight loss with a high-fat or low-fat diet composition
Schübel et al,⁴¹ 2018	150	Obese	I	12 wk	6.4	2-d fast (25% of calorie requirements) and 5-d usual diet vs CR and control group; 12-wk maintenance; 26-wk follow-up; self-reported	Weight loss and maintenance is similar in IF and CR
Sundfør et al,⁴² 2018	112	Obese	I	26 wk	8.4	2-d fast (20% of calorie requirements) and 5-d usual diet vs CR; 26-wk maintenance; self-reported	Weight loss and maintenance are similar in IF and CR
Trepanowski et al,⁴³ 2017 Trepanowski et al,⁴⁴ 2018 Kroeger et al,⁴⁵ 2018 Kalam et al,⁴⁶ 2019	79	Obese	I	24 wk	6.0	Alternated 25% of usual calorie intake with 125% of usual calorie intake vs CR and control group; 24-wk follow-up; self-reported	IF promotes weight loss and weight maintenance similar to CR
Varady et al,⁴⁷ 2009 Bhutani et al,⁴⁸ 2010	16	Obese	II	8 wk	5.8	Alternated 25% of energy needs with ad libitum caloric intake; self-reported	IF is a viable option for weight loss in obese individuals
Varady et al,⁴⁹ 2013	30	Obese	I	12 wk	6.5	Alternated 25% of baseline energy needs with ad libitum caloric intake vs usual diet; monitored	IF is effective for weight loss in obese individuals
Zuo et al,⁵⁰ 2016	40	Obese	II	12 wk	10.0	1-d fast (430 kcal) and 6-d high-protein diet; 52-wk follow-up; monitored	IF with a high-protein diet is effective for weight loss, with low risk of weight regain

CR—calorie restriction, HbA_1c—hemoglobin A_1c, IF—intermittent fasting, T2D—type 2 diabetes.
↵* Where sex is not specified, both men and women were enrolled.
↵† Self-reported indicates participants reported consumption in food diaries; monitored indicates investigators monitored participants’ consumption.

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Table 2.

Outcomes of risk factors for cardiovascular disease and type 2 diabetes in 26 individual studies of 22 intermittent fasting trials enrolling obese adults without type 2 diabetes

RISK FACTOR	OUTCOME	N	STUDIES
Blood pressure	↔	324	Examined in 16 studies, with no change in 9 studies^{10,13,27,29,35,37,42,43,47}
Blood pressure	↓	226	Examined in 16 studies, with a decrease in 7 studies^{11,15,21,24,25,49,50}
Body weight	↓	764	Decrease seen in 22 studies^{10,11,13,15,19,20,22–25,27–29,33,35,37,41–43,49,47,50}
BMI	↓	566	Decrease seen in the 16 studies measuring BMI^{10,13,15,19,20,23–25,28,29,35,37,42,43,47,50}
Diabetes
• Glucose level	↔	409	Examined in 17 studies, with no change in 11 studies^{10,19,24,25,27,32,35,38,40,42,43}
	↓	192	Examined in 17 studies, with a decrease in 5 studies^{13,15,20,23,41}
	↑	24	Examined in 17 studies, with an increase in 1 study¹¹
• HbA_1c level	↓	54	Decrease seen in the 1 study measuring HbA_1c level⁴²
• Insulin level	↓	407	Decrease in 8 studies, decreasing trend in 3 of 11 studies measuring insulin level^{11,13,15,19,20,25,27,32,35,41,43}

BMI—body mass index, HbA_1c—hemoglobin A_1c.

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Table 3.

Outcomes of risk factors for cardiovascular disease and type 2 diabetes in 5 intermittent fasting studies enrolling obese adults with type 2 diabetes

RISK FACTOR	OUTCOME	N	STUDIES
Blood pressure	NA	NA	Not studied in obese patients with type 2 diabetes
Body weight	↓	174	Decrease seen in all 5 studies^{12,16,17,21,34}
BMI	↓	174	Decrease seen in all 5 studies^{12,16,17,21,34}
Diabetes
• Glucose level	↓	78	Decrease seen in the 3 studies measuring glucose level^12,21,34
• HbA_1c level	↓	164	Decrease seen in the 4 studies measuring HbA_1c level^16,17,21,34
• Insulin level	↓	27	Decrease seen in the 1 study measuring insulin level³⁴