Cutting sleep by 80 minutes a night increased body weight and waist circumference in adults with cardiometabolic risk factors.
Insomnia takes a toll on metabolism, but the effects 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 weight and body composition.
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The analysis combined two randomized trials involving 95 adults who normally slept at least seven hours and had elevated risk for heart and metabolic disease. Each participant completed two six-week periods: 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 weight and waist size, used magnetic resonance imaging (MRI) scans to estimate fat and muscle distribution, tracked activity, and measured fasting hormones related to appetite and energy stores. In 34 participants, the researchers also used the doubly labeled water technique, in which participants drank water containing traceable forms of hydrogen and oxygen, to estimate energy expenditure.
- 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 activity were limited to sedentary time. Participants spent about 17 more minutes per day sedentary, while their moderate-to-vigorous activity did not clearly change.
- Total daily energy expenditure did not clearly change. Estimated energy use averaged about 2,439 calories per day during shorter sleep and 2,415 during adequate sleep. The statistical uncertainty was too large to establish a reliable difference.
- Hormones involved in appetite regulation showed no consistent response. Leptin (a hormone signaling energy stores) was modestly higher, but two other appetite-related hormones (GLP-1 and Ghrelin) did not clearly change.
A longer waking day can create more opportunities for 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 detectable change in total daily calorie use. The hormone findings did not point to a separate appetite-driven mechanism. Leptin increased alongside body weight, consistent with greater energy stores, while ghrelin and GLP-1 did not clearly change.
The main limitation is that this was a short study that did not measure calorie intake, so it cannot clearly explain what caused the weight difference or whether it would last. Still, the results suggest that even a small loss of sleep may be enough to shift weight over a matter of weeks. In Aliquot #104, you can explore the science of optimizing sleep.