Researchers asked 95 adults who usually slept at least seven hours to try two six-week schedules. In one, participants kept their usual sleep. In the other, they delayed bedtime by 90 minutes while keeping wake time steady. The order was randomized, and each person completed both schedules with a four- to six-week break between them. Wrist monitors showed that the shorter-sleep phase reduced sleep by about 78 minutes a night.

Compared with the adequate-sleep phase, the shorter-sleep phase was associated with an average body-weight increase of 0.45 kilograms and a waist-circumference increase of 0.52 centimeters. Participants also spent about 17 more minutes per day sedentary. The study did not find a change in the percentage of whole-body volume made up of fat or skeletal muscle, and moderate-to-vigorous activity time did not change.

Those details matter because this was not a study of cravings or specific food choices. Food intake was not directly measured in the pooled analysis, so the results cannot show which eating behaviors, if any, explained the weight difference. The researchers also caution that the sample was small, most participants were women, everyone started with elevated cardiometabolic risk, and six weeks may be too short to detect changes in body composition.

The experiment strengthens the case that a realistic stretch of shorter sleep can modestly affect weight regulation and daily movement in some adults. It does not show that one restless night changes eating, nor does it establish what would happen over months or years.