The standard explanation for why short sleep leads to weight gain centers on appetite: less sleep disrupts hunger hormones, so people eat more. A new randomized trial from Columbia University Irving Medical Center, published July 7 in Annals of Internal Medicine, complicates that story. It found that mildly sleep-restricted adults gained weight without eating any more than they did when well-rested — the weight came from moving less.
The Trial
Researchers led by Faris Zuraikat, with senior author Marie-Pierre St-Onge, recruited 95 adults who typically slept 7 to 8 hours a night and who were at elevated cardiometabolic risk. Using a crossover design, each participant completed two six-week phases: one in which they delayed their normal bedtime by 90 minutes, and one in which they kept their usual sleep schedule. In practice, the delayed-bedtime phase produced an average sleep loss of about 80 minutes per night — not the full 90, since participants didn't fall asleep instantly.
At the end of the sleep-restricted phase, participants had gained an average of one pound, along with a body composition shift, compared with the adequate-sleep phase. The trial tracked not just weight but activity levels, caloric intake, and a panel of metabolic hormones to identify the actual driver.
Moving Less, Not Eating More
The result ran counter to the appetite-driven explanation that dominates the literature. Caloric intake did not increase in a meaningful way during the sleep-restricted phase. What changed was activity: participants were measurably more sedentary during their additional waking hours, even after accounting for the simple fact that being awake longer gives more opportunity to sit.
"Even when we accounted for the fact that they were awake longer when sleep was shortened, participants spent more time being inactive than when they got adequate sleep," Zuraikat said. "This is notable, as people who are more sedentary have elevated risk for chronic diseases."
On the hormone panel, leptin — which signals how much energy the body has stored — rose alongside the weight gain, consistent with leptin's known role as a marker of increasing fat mass rather than a cause of it. Ghrelin, the hormone that drives hunger, trended slightly lower, not higher, and GLP-1, tied to feelings of fullness, barely moved. None of the appetite-related hormones shifted in a direction that would explain increased eating — because increased eating didn't happen.
Why the Mechanism Matters
Distinguishing "eating more" from "moving less" isn't just academic. Interventions built around the appetite theory — portion control, hunger-hormone-targeted counseling — would misfire if the real driver of sleep-loss-related weight gain is behavioral inactivity rather than biological hunger signaling. The Columbia findings suggest that clinicians counseling patients on sleep and weight might get more traction by addressing daytime movement and sedentary behavior directly, rather than assuming the fix is simply eating less.
The study was supported by the American Heart Association and the National Institutes of Health, and the sleep loss involved was modest and common — the kind of gradual bedtime creep that affects many adults with demanding schedules, not an extreme deprivation protocol.
What This Means for Patients
An 80-minute nightly sleep deficit is a small, easy-to-overlook habit — a later bedtime scrolling on a phone, an early alarm that isn't compensated for — and this trial suggests it's enough to shift body weight within six weeks. For anyone trying to manage weight while also running short on sleep, the practical takeaway is to pay attention to daytime activity levels specifically, not just diet. Because the sedentary shift showed up even after accounting for extra waking hours, simply "trying to eat the same" while sleep-deprived may not be enough to prevent gradual weight gain — deliberately maintaining physical activity during sleep-restricted stretches may matter just as much as protecting the sleep itself.
