New evidence links modest sleep loss to weight gain and sedentary behaviour

A six-week Columbia University trial reveals that even slight reductions in sleep duration can lead to weight increase and increased inactivity, highlighting the importance of sleep for weight management, especially among teenagers.

A six-week Columbia University trial has given some of the clearest experimental evidence yet that even fairly ordinary sleep loss can push body weight upwards. Adults at elevated cardiometabolic risk who cut about 78 minutes from their nightly sleep gained roughly 0.45kg, added about half a centimetre to their waistlines and spent more time sitting. Researchers at the University of Colorado Anschutz say the finding matters well beyond the lab, particularly for teenagers whose school routines often clash with the later body clocks of puberty.

The Columbia analysis, published in Annals of Internal Medicine in July 2026, pooled two randomised crossover trials involving 95 adults aged 20 and older who usually slept at least seven hours. Each participant completed one six-week period of adequate sleep and another in which bedtime was pushed back by around 90 minutes, with a washout in between. Sleep and movement were tracked with wrist actigraphy and diaries, while researchers measured weight, waist circumference, MRI-based body composition and appetite-related hormones.

What changed was not everything. Leptin rose during the short-sleep phase, while ghrelin drifted down slightly and GLP-1 did not shift significantly. MRI scans showed no clear redistribution of body fat or muscle over the six-week window, and time spent in moderate-to-vigorous exercise was broadly unchanged. Instead, the weight gain appeared to come alongside more inactivity: participants averaged about 17 extra sedentary minutes a day, and nearly 30 minutes among men and postmenopausal women, according to coverage by National Geographic and Medical News Today.

That modest deficit is precisely why outside specialists say the study deserves attention. “There’s a lack of understanding of how much sleep affects weight,” Taruj Ali of SOMOS Health and Mary Washington Health System told National Geographic. “Of course, diet and exercise are important. But sleep is part of the trifecta for weight management.” Wired, citing a Columbia release, reported Marie-Pierre St-Onge saying: “Our study shows that getting adequate sleep may help reduce the risk of weight gain and obesity-related conditions like heart disease and diabetes.” Faris Zuraikat, the paper’s lead author, said the roughly half-kilo rise over six weeks was comparable to the average annual weight change seen in young to middle-aged adults.

The study does not settle everything. It excluded people with diagnosed sleep disorders and diabetes, and its effects were modest over a relatively short period. Brian Wojeck, a Yale assistant professor of medicine and sleep-disorder specialist, told National Geographic: “This study gives us a glimpse into what might be happening, but the truth is for many of our patients, it’s not just six weeks. It’s all the time. Most of our patients that we see in a sleep clinic are chronically sleep-deprived.” The Annals paper itself said it may have been too short to detect body-composition changes and was not powered to pin down differences between groups.

For adolescents, researchers at CU Anschutz argue, the pressures are sharper. Their September 2026 campus briefing said seven in 10 teenagers are missing the recommended eight to 10 hours of sleep, not simply because of poor habits but because puberty shifts circadian timing later. The American Academy of Pediatrics has long recommended that middle and high schools begin no earlier than 8:30am, yet Stacey Simon told CU Anschutz that “A majority of schools start much earlier than that. Certainly, what we see in our sleep clinic at Children’s (Hospital Colorado) is that, during the school year, teens are forced to sleep outside of their biological clock.” Anxiety, crowded schedules and evening screen use can push bedtimes later still.

CU Anschutz casts that as part of a much bigger obesity story. Its report said nearly three-quarters of US adults meet the criteria for overweight, while more than 40% of adults and 22% of teenagers meet the criteria for obesity. Simon said short sleep and late sleep timing in adolescents are linked to poorer insulin sensitivity, which over time can raise the risk of obesity and type 2 diabetes. Medical News Today reported that related analyses in the same Columbia cohort have already found increased insulin resistance in women with elevated cardiometabolic risk, alongside signs of heart inflammation after chronic mild sleep restriction.

There are also hints that sleep loss may not land evenly across teenagers. Simon’s group has found that adolescent girls tend to show earlier circadian timing than boys while also reporting more insomnia, a combination that could mean greater sleep need but less chance of meeting it. Seth Creasy, Simon’s colleague at CU Anschutz, summed up the emerging consensus when he said: “So diet and physical activity are still the two main drivers of weight gain from a behavioral standpoint, but sleep can help support both of those.” That is a more restrained message than claiming sleep is a cure-all, but it is also more practical: as consumer-health coverage of the Columbia study noted, keeping a regular schedule, cutting late-night screen use, limiting caffeine and alcohol close to bedtime, and checking for untreated sleep disorders may be as important to long-term weight control as the advice people are more used to hearing about food and exercise.