78 Minutes Less Sleep Nightly Tied to 0.45 kg Gain Over Six Weeks in At-Risk Adults

Researchers at Columbia University combined two randomized crossover trials of 95 adults who normally slept seven or more hours. Each participant completed six weeks of adequate sleep and six weeks of sleep restriction in which bedtime was delayed 1.5 hours; actigraphy, diaries, MRI, waist measures, and hormone assays were obtained before and after each period. Participants gained a mean 0.45 kg during restriction versus adequate sleep, with a 0.5 cm waist increase and higher sedentary time; leptin and ghrelin shifts were recorded but energy expenditure data were limited to a subgroup. The design isolates sleep duration while holding other behaviors constant. Observational cohorts have long linked short sleep to higher BMI, yet few interventional studies quantify acute effects in weeks. This trial supplies within-person evidence that modest, repeated sleep loss alters weight and activity before overt metabolic change appears. Next steps require longer follow-up, objective energy-intake tracking, and testing whether restoring sleep reverses the gain; replication in lower-risk groups would clarify generalizability.