What intermittent fasting is
Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. It makes no prescriptions about what to eat — only when. The most studied versions are: 16:8 (eating within an 8-hour window), 5:2 (eating normally for five days and restricting to around 500-600 calories on two non-consecutive days) and alternate day fasting.
What the evidence shows
For weight loss, IF works about as well as continuous calorie restriction, and no better. A 2022 NEJM study found no significant difference in weight loss between time-restricted eating and standard calorie restriction at one year when calories were matched. The mechanism appears to be simply reduced calorie intake — most people find it easier to eat less when their eating window is smaller.
Who it might suit
For some people, time-restricted eating is psychologically easier than continuous calorie counting — skipping breakfast and eating from noon to 8pm requires no tracking, just clock-watching.
Who should avoid it
IF is not appropriate for pregnant or breastfeeding women, children and adolescents, people with a history of eating disorders, people with type 1 diabetes or those on medications that require food.