The researchers, a collaboration of scientists based in Boston, Massachusetts, and the Republic of Korea, sought to determine if what they refer to as “catch-up sleep” impacts body mass index (BMI) in the general population. To do so, they conducted face-to-face interviews of a random sampling of 2,156 adults, comparing their sleep habits with their BMI scores. The 932 participants who slept in—”catch-up sleepers” (people who sleep longer on the weekend than on weekdays by approximately two hours) had a significantly lower BMI than the other subjects. What’s more, every additional hour of catch-up sleep was associated with a decrease in BMI.
As to why sleeping in on weekends can lead to weight loss, one of the study co-authors, Robert Thomas, MD, MMSc, of the Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine at the Beth Israel Deaconess Medical Center in Boston, reminded Reader’s Digest of the “substantial experimental and epidemiological data that short sleep contributes to weight gain.” He notes, “our best estimate [as researchers] is that there is a balance to be kept, and the body can adjust and adapt within reason. Catch-up sleep allows the basic balance to be maintained.”
Accordingly, Dr. Thomas suspects that intermittent catch-ups during the week would have the same effect. However, as he points out, the reality is that most of us don’t have time for cat-naps mid-week and are left to catch up on sleep over the weekend.
Although the study showed significant differences in BMI with the addition of two or more hours of catch-up sleep, Dr. Thomas points out that there are “substantial individual differences,” such that the benefit we get from those extra hours will vary depending on how much sleep each of us generally needs. “To determine your optimal sleep, you can track the time spent sleeping on nights when there is no need to wake up to an alarm,” suggests Liza Baker, a health coach at Simply Health Coaching. That tells you about how many hours of sleep your body likes to get, since it varies greatly across the population, from just 4 to 5 hours to 9 to 10 hours. (Most adults fall in the 6- to 8-hour range.)
So can you actually lose weight by sleeping in on the weekend? Only if you’re paying off a sleep debt from the week, according to the results of this study. It helps if you’re also eating less, Dr. Thomas adds.