Which “flavor” of intermittent fasting is the most effective for weight loss? Original paper

Traditional weight-loss diets typically advocate consuming 500–750 calories less each day — known as calorie restriction. Recently, intermittent fasting (IF) has gained popularity as an “alternative” weight-loss method that may have additional benefits for metabolic health and longevity.^[1]

However, many variations of IF exist, including alternate-day fasting (ADF), the 5:2 diet, and time-restricted eating (TRE). A comparison of the effects of these different types of IF and how they compare to calorie restriction for weight loss was needed.

This meta-analysis compared the effects of different dietary regimens for weight loss in adults with normal weight or overweight/obesity. A total of 24 studies involving 1,768 participants were included in the meta-analysis.

Three IF diets and two comparator diets were included: (i) ADF/modified ADF (12 studies), (ii) the 5:2 diet (8 studies), (iii) TRE (4 studies), (iv) calorie restriction (15 studies), and (v) ad libitum eating (i.e., no dietary restriction; 9 studies). The study durations ranged from 3 to 26 weeks.

The primary outcome was weight loss. As a secondary outcome, dietary adherence was assessed for each diet.

ADF/modified ADF ranked the highest as most effective for weight loss, followed by calorie restriction and then TRE.

ADF/modified ADF, the 5:2 diet, and TRE all led to a similar amount of weight loss — with a range of 0.8%–12.9% of body weight for ADF/modified ADF, 1.7%–7.9% for the 5:2 diet, and 0.9%–8.6% for TRE.

There were no differences in weight loss when comparing any of the IF diets to calorie restriction. Adherence was similar among all of the dietary regimens.

Rates of adherence were not statistically analyzed in the meta-analysis but were reported for each study individually. In studies lasting 3 months or shorter, adherence was 80%–98% for ADF/modified ADF, 80%–90% for calorie restriction, 73%– 80% for the 5:2 diet, and 60%–90% for TRE.

Thus, although it appears that ADF/modified ADF and calorie restriction had the highest participant adherence, this finding needs to be more rigorously studied in the future because not all trials include these outcomes.