According to a small study published in the American Journal of Clinical Nutrition, changes in metabolism and physical activity during fasting in the month of Ramadan did not lead to weight loss. During Ramadan, observant Muslims abstain from eating and drinking from dawn to dusk, providing researchers a natural experiment to observe the effects of intermittent fasting on body weight. Previous studies have observed mixed results, from no weight loss to modest but temporary weight loss.
The study involved 13 men and 16 women who underwent tests for resting metabolism and total daily calories burned during Ramadan and the month after. Participants burned fewer calories at rest after the first week and were about 10% less active during the fasting period as measured by step-counting devices worn by some participants in the study.
Overall, the month of fasting did not lead to weight loss. This may be because any fewer calories consumed during fasting were offset by compensatory eating at night. Also, less sleep during Ramadan may have offset the effects of decreased resting metabolism and physical activity.