A new pooled analysis of two randomized controlled trials provides the strongest causal evidence to date that chronically sleeping less than one’s body needs may directly lead to weight gain. Adults who cut their sleep by roughly 78 minutes per night for six weeks gained nearly half a kilogram in body weight and showed measurable increases in waist circumference and total body volume, according to the findings published July 7 in _Annals of Internal Medicine_.
The study, led by researchers at Columbia University Irving Medical Center, pooled data from two rigorously designed crossover trials involving 95 adults age 20 and older who had elevated cardiometabolic risk and habitually slept seven or more hours per night. Each participant completed two six-week phases: one with adequate sleep and one with a 1.5-hour reduction in nightly sleep, separated by a multiweek washout period. The crossover design, in which each person serves as their own control, substantially strengthens the causal inferences that can be drawn.
What they found
Sleep restriction produced consistent shifts across multiple anthropometric and behavioral measures. Compared with adequate sleep, the six-week restriction period was associated with:
- Body weight increase of 0.45 kg (95% CI: 0.33 to 0.57)
- Waist circumference increase of 0.52 cm (95% CI: 0.25 to 0.79)
- Whole-body volume increase of 0.56 L (95% CI: 0.19 to 0.93)
- Leptin elevation of 2.03 ng/mL (95% CI: 0.38 to 3.68)
- Sedentary time increase of 17.2 minutes per day (95% CI: 11.7 to 22.7)
Participants achieved an average sleep reduction of 78.4 minutes per night (95% CI: -83.5 to -73.3), closely matching the protocol’s target of 90 minutes. Adiposity was assessed via MRI, and the researchers also tracked energy balance biomarkers and physical activity.
The leptin finding is noteworthy. Leptin, a hormone produced by fat cells, signals satiety to the brain; higher circulating levels typically reflect greater body fat mass. The observed increase is consistent with the weight and adiposity changes, though the researchers caution that the relationship may be complex and bidirectional.
Why it matters
Obesity remains one of the most pressing public health challenges of the century, and sleep has increasingly been recognized as a potential lever alongside diet and exercise. However, most evidence linking short sleep to weight gain has come from observational studies, which cannot prove cause and effect. The present analysis, built on randomized crossover trials, closes that gap.
“This pooled analysis provides high-causal evidence that prolonged moderately short sleep leads to weight gain,” the authors write. The effect sizes were modest but clinically meaningful at the population level. A half-kilogram increase over six weeks, if sustained or compounded over months and years, could translate into a substantial shift in body weight and cardiometabolic risk.
The findings also carry implications for how clinicians approach weight management. Current guidelines emphasize calorie restriction and increased physical activity, but the authors suggest that “weight management and cardiometabolic disease prevention programs should consider incorporating sleep strategies to promote adequate sleep.” For people struggling to lose or maintain weight, optimizing sleep duration may be an overlooked but accessible intervention.
Limits
The authors note several limitations. The six-week intervention may have been too short to detect changes in body composition, which often takes longer to manifest than shifts in overall body weight. The pooled sample, while larger than either trial individually, had limited statistical power to evaluate subgroup differences by sex or menopausal status. Effect sizes were modest across all measured outcomes, and the clinical significance of individual changes should be interpreted cautiously.
Bottom line
A six-week period of moderately reduced sleep (about 1.3 hours less per night) led to measurable increases in body weight, waist circumference, and sedentary time in adults at elevated cardiometabolic risk. The findings add weight to the argument that sleep should be treated as a core component of weight management, alongside diet and activity. Even modest, sustained reductions in sleep may accumulate into meaningful changes over time.
Source
Faris M Zuraikat, Samantha E Scaccia, Justin A Cochran, Bin Cheng, Keith M Diaz, Seth A Creasy, Edward L Melanson, Wei Shen, Brooke Aggarwal, Sanja Jelic, Marie-Pierre St-Onge. “Prolonged Short Sleep and Its Effect on Body Weight and Composition: A Pooled Analysis of Randomized Trials.” _Annals of Internal Medicine_, July 7, 2026. DOI: 10.7326/ANNALS-25-01660. PMID: 42407080. ClinicalTrials.gov: NCT02960776, NCT02835261. Funding: National Institutes of Health and American Heart Association.