Regularly skimping on sleep may lead to weight gain and a larger waistline, new research found.
In a recent study, adults who stayed up even a little late every night for six weeks but woke up at their regular time gained an average of 1 pound.
While that amount of weight gain may seem small, it’s important to note that it happened over a relatively short period, says senior author Marie-Pierre St-Onge, PhD, a professor of nutritional medicine at Columbia University Irving Medical Center in New York City.
The adults were losing about 80 minutes of sleep per night. If the same pattern repeated for a full year, it could eventually result in more than 8 added pounds for some people — “clinically meaningful weight gain,” according to the study authors.
Researchers Intentionally Cut Sleep Short to Measure Impact on Weight and Hormones
While other studies have looked at the effects of more extreme sleep deprivation, researchers wanted to know how a real-world shortened sleep scenario might affect weight and metabolism.
The study pooled data from two randomized trials that included 95 adults who were 34 years old on average. Before the study, participants usually slept at least seven hours a night and had elevated cardiometabolic risk, meaning risk factors tied to heart disease or carrying excess weight.
Each person completed two six-week sleep phases:
- Adequate sleep, when they kept their usual bedtime and wake time
- Shortened sleep, when they delayed bedtime by a little more than an hour while keeping the same wake time
Participants wore wrist monitors to track sleep and movement, and researchers also measured their weight, waist size, muscle-to-fat ratio, physical activity, time spent sitting, and hormones related to appetite and energy.
Because each person went through both schedules, researchers could compare what happened when the same participant got enough sleep versus when they stayed up late.
Less Sleep Was Tied to Weight Gain and More Sitting
During the shortened-sleep phase, participants slept about 78 fewer minutes per night on average — going from about 7.5 hours to a little over 6 hours.
On average, participants experienced the following during their shortened sleep phase:
- A 0.45 kilogram (1 pound) weight gain
- A small increase in waist size (about one-fifth of an inch)
- 17 more minutes a day spent sitting, even after researchers accounted for the fact that they were awake longer
- Higher leptin levels, a hormone that tends to rise as the body stores more energy
These findings highlight the very important role of sleep for overall health, particularly weight, says Yuval Pinto, MD, an obesity and family medicine doctor at Johns Hopkins Medicine in Baltimore, who was not involved in the research.
“Sleep is so underestimated in our society. It’s the second most important aspect when it comes to weight loss after nutrition, a very important piece of the puzzle,” says Dr. Pinto.
How Too Little Sleep Could Contribute to Weight Gain
Weight gain usually reflects a shift in energy balance — how much energy the body takes in versus how much it uses, says Dr. St-Onge.
In this study, people spent more time sitting when their sleep was shortened. In previous research, St-Onge’s team has found that people tend to eat more when sleep is restricted.
“I think both come into play when it comes to insufficient sleep,” she says.
Pinto sees that pattern in his practice, too. “When people sleep less or have lower-quality sleep, hunger and the need to snack go up,” he says.
Hormones may be one reason. Leptin and ghrelin help regulate hunger and fullness, and poor sleep can disrupt that system, Pinto says. This study did not find a clear change in ghrelin, a hunger-related hormone, or GLP-1, a hormone involved in fullness and blood sugar control. But the researchers noted that fasting morning hormone levels may not capture how these hormones rise and fall across the day.
The Study Has Some Limitations
The study has several important strengths: It was randomized, each person served as their own comparison, and sleep changes were recorded at home rather than only in a sleep lab.
Researchers also used wrist monitors, body scans, and other measurements, rather than relying only on what people remembered or reported.
But there were also limitations. At just six weeks, it was short, and the number of participants was relatively small. It also included only adults with elevated cardiometabolic risk, so the results may not apply to everyone. It was also not designed to prove why people gained weight.
Signs You May Not Be Getting Enough Sleep
You don’t need a sleep tracker to know your sleep is falling short.
St-Onge says signs that you may need more sleep include:
- Yawning and trouble staying awake or alert
- Dozing off during quiet moments, like while you’re reading, watching TV, or sitting in traffic
- Feeling moodier or more irritable than usual
- Waking up unrefreshed
- Trouble concentrating
- Sleeping longer when you give yourself more time in bed
Your Bed Should Be for Sleep and Sex Only
Pinto tells his patients that the bed should be reserved for two activities: sleep and sex.
Other top ways to improve your sleep, according to Pinto:
- Wait until you’re tired to go to bed.
- Keep your room cool and dark.
- Stop eating a couple of hours before your bedtime to allow time for digestion.
He also recommends getting screened for underlying sleep issues. For example, obstructive sleep apnea is common in people who are overweight or have obesity. “If that goes undiagnosed and untreated, that can make it very hard to lose weight,” says Pinto.
Loud snoring, morning headaches, waking up feeling unrefreshed, and daytime sleepiness are all potential signs of an underlying sleep disorder, he says.
Going through perimenopause or menopause can also negatively affect sleep, Pinto points out. “If you’re waking up sweating and your pillow is damp with sweat, that’s something that needs to be discussed, diagnosed, and treated,” he says.
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