Intermittent fasting is likely to result in no or only minimally higher weight loss in adults with overweight or obesity than conventional diets with continuous calorie reduction. Compared to no structured change in diet, a small effect is likely. This is the result of a new systematic Cochrane review published today, Monday.

The evaluation includes 21 randomized controlled trials with a total of 1430 participants for comparison with other diets. There may have been no or only a slight difference in body weight. The authors rate the trustworthiness of this evidence as low, partly because of methodological weaknesses and small samples in many studies.

When compared with no targeted nutritional intervention (six studies, 427 participants), intermittent fasting probably resulted in an average weight loss of about 3.4 percent higher. The authors classified this evidence as moderately trustworthy. With a starting weight of 100 kilograms, this would mean about 3.4 kilograms more. However, a loss of at least five percent is usually considered clinically significant in guidelines.

The review summarizes various forms of intermittent fasting, including time-restricted eating (usually 8 to 10 hours of eating windows per day), periodic fasting (one to two fasting days per week), alternating fasting (alternating fasting and normal days), and modified variants such as the 5:2 diet (two days of greatly reduced calorie intake per week).

Almost all of the included studies ran for only six to twelve months. It is therefore not possible to make statements about long-term weight maintenance, satisfaction and perseverance in everyday life, undesirable effects or effects on concomitant diseases such as type 2 diabetes.

“For some people, intermittent fasting may be an option,” explained Luis Garegnani, director of the Cochrane Center at the Universidad Hospital Italiano de Buenos Aires and one of the authors. However, the current evidence does not justify the strong enthusiasm in social media.

Prof. Dr. Jörg Meerpohl, Scientific Director of Cochrane Germany in Freiburg, added that data on long-term health benefits were lacking. It also remains unclear whether intermittent fasting reduces the risk of obesity in the long term.

In Germany, according to the Robert Koch Institute (data 2019/2020), almost half of women and more than half of men are affected by overweight (including obesity), and just under a fifth of adults are obese.

Original Paper:

Intermittent fasting for adults with overweight or obesity – Garegnani, LI – 2026 | Cochrane Library

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