Sleep enough if you want to lose fat when you lose weight

An article in this week's Annals of Internal Medicine studied physiologic responses in 10 dieting adults, 5 of whom slept 5 1/2 hours per night and 5 who slept 8 hours a night. The article showed that the 5 who slept less lost 55% less fat than the ones assigned to sleep more despite taking in the same number of calories and losing similar total amounts of weight. Instead they lost more non-fat body mass pounds to make up the difference.

This study included only 10 people, and excluded people who drank a lot of caffeine. Therefore, it is unclear how generalizable the study is.

This study has been extensively misreported as showing that lack of sleep leads to less weight loss while dieting rather than the percent body fat lost. Nonetheless, it suggests that if you are dieting, you may wish to make sure you get enough sleep so that you lose fat instead of non-fat mass. The study should be repeated in a larger sample.