Cutting sleep by 80 minutes per night increased body weight and waist circumference in adults with cardiometabolic risk factors. Digest
Sleep disorders can promote weight gain, but the effect of the mild sleep loss many people experience in daily life is less certain. A new study tested whether restricting sleep by a little over an hour could change body weight and composition.
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The analysis pooled data from two randomized trials involving 95 adults who normally slept at least seven hours and had elevated risk for heart and metabolic disease. In both trials, participants followed two six-week sleep schedules in a random order: one with their usual sleep and one with bedtime delayed by 1.5 hours. Wrist sensors confirmed that the shorter sleep period reduced nightly sleep by about 78 minutes, to just over six hours. Researchers measured body weight and waist size, used magnetic resonance imaging (MRI) scans to estimate body fat and muscle distribution, tracked physical activity, and measured morning fasting levels of hormones related to appetite regulation and energy stores. In 34 participants, they also estimated energy (calorie) expenditure using the doubly labeled water technique, in which participants drank water containing traceable forms of hydrogen and oxygen.
- Short sleep modestly increased weight without a clear shift in body composition. After six weeks, participants were about 1 pound (0.45 kg) heavier and had waists about 0.5 cm larger under shorter sleep, but MRI scans did not show a clear shift in body fat or skeletal muscle proportions.
- Changes in physical activity were limited to sedentary time. Participants spent about 17 more minutes per day sedentary, while their moderate-to-vigorous physical activity was nearly identical under both sleep conditions.
- Total daily energy expenditure remained unchanged. Estimated energy use averaged about 2,439 kilocalories (kcal) per day during the shorter sleep period and 2,415 kcal during the adequate sleep period.
- Hormones involved in appetite regulation showed no consistent response. Leptin (a hormone that also reflects energy stored in body fat) was modestly higher with shorter sleep, but two other appetite-related hormones, GLP-1 and ghrelin, did not clearly change.
One possible explanation for this result is that more waking hours can create more opportunities to consume meals and snacks, while more sedentary time may offset some of the extra energy required to stay awake. Together, these shifts could create a small daily calorie surplus that accumulates over time, allowing weight to rise without a clear change in total daily calorie use. The hormone findings did not point to a separate appetite-driven mechanism. Of the three appetite-related hormones measured, only leptin increased, a change that may reflect the modest weight gain rather than a broader shift in appetite signaling.
A key limitation is the study's relatively short duration and lack of calorie intake measurements, which make it difficult to clearly explain the observed weight difference or determine whether it would persist under these sleep conditions over time. Still, the results suggest that even a small loss of sleep may be enough to shift weight over a matter of weeks. Aliquot #104 explores the science of optimizing sleep.