Is intermittent fasting worth it?

Intermittent fasting is an umbrella term for eating schedules that restrict meal timing: alternate-day fasting, two fasting days per week (5:2), or time-restricted eating such as 16:8. The clearest benefit is weight loss. All schedules work for that purpose, and the effect is comparable to a conventional low-calorie diet that you stick to consistently^1,2,3.

Not every schedule works equally well. Alternate-day fasting scores slightly better in studies than continuous calorie restriction, by an average of around 1.3 kg, and approximately 1.7 kg more than time-restricted eating. However, that advantage is small, and after 24 weeks the difference compared with other diets disappears entirely¹. The method you can sustain the longest wins in the long run.

For blood sugar there are positive signals: fasting lowers fasting blood glucose and insulin. Whether it also improves blood sugar control over months has not been demonstrated consistently^1,3,2. Results for blood lipids are mixed. Alternate-day fasting lowers cholesterol and triglycerides, but time-restricted eating actually showed a small increase in bad cholesterol compared with daily fasting^1,2.

Watch out for muscle loss. In addition to fat, intermittent fasting also causes you to lose muscle mass. This is a particular risk for older adults or anyone who wants to preserve muscle². Early indications suggest that combining fasting with strength training limits this drawback and enhances the metabolic benefits, but this has so far only been studied in a limited number of studies⁴.

What intermittent fasting has not demonstrated so far: a longer life or fewer heart attacks in humans. Animal studies provide promising signals, but direct evidence in humans is lacking. Studies in humans measure intermediate markers such as weight and blood sugar, not hard outcomes like strokes or mortality^2,1,5,4. Side effects have not yet been well mapped, so be cautious if you belong to a vulnerable group.