If you have a late dinner and then head to bed, beware: You may gain weight while you sleep, a new study suggests.
That's most likely because your metabolism slows, boosting blood sugar and other chemicals that contribute to weight gain and type 2 diabetes, researchers say.
"It's not just what you eat, but when you eat that may be a factor in promoting conditions like obesity," said study author Dr. Jonathan Jun, an associate professor of medicine at Johns Hopkins University in Baltimore. "You might eat this same number of calories in that 24-hour period, but your body will handle those calories differently depending on what time you eat them."
For the study, Jun's team asked 20 healthy volunteers to eat the same dinner at 6 p.m. or 10 p.m. Both groups went to bed at 11 p.m. and got up at 7 a.m.
Before the study, participants wore activity trackers. During the study, blood samples were taken hourly and sleep studies were conducted. The volunteers also had scans of body fats and ate foods containing compounds that allowed researchers to track fat burning.
The upshot: Late diners had higher blood sugar and burned less fat.
On average, their peak blood sugar level after a late dinner was about 18% higher, and the amount of fat burned about 10% lower, compared with eating earlier, the study found.
These effects might be even greater for people who are obese or have diabetes, Jun said.
What's not clear is whether it's the interval between eating time and bedtime that accounts for the difference, he said.
For example, if you have dinner at 10 p.m. but retire at 3 a.m., is that biologically the same as dinner at 6 p.m. and bed at 11 p.m.?
And, Jun said, the effects of eating and sleeping might differ for each person based on their personal metabolism or body clock.
"Instead of getting fixated on what time is late or what time it is on the clock to start or stop eating, we need to recognize that it is very dependent on the individual," he said.
Jun said he hopes to learn more in future studies.
Samantha Heller, a senior clinical nutritionist at NYU Langone Health in New York City, reviewed the findings.
"It makes sense that eating close to bedtime alters glucose and fat metabolism, because you are sleeping and not physically active," she said, adding that sleep has its own processes that involve cellular and molecular mechanisms to help the body stay healthy.
Heller noted that people often get stuck in a routine of eating before dinner, eating dinner, and then snacking until bedtime -- which means they have been eating for several hours.
"It is an easy way to pack on the pounds," she said. "We eat at night for many reasons, including stress, boredom, loneliness and anger."
To help manage nighttime munching, Heller suggests planning an afternoon snack like hummus and carrots, so you are not starving by dinnertime, and enjoying a balanced, more plant-based dinner. Then close the kitchen.
"Plan activities for those moments when you have an urge to grab a snack -- it is unlikely you are hungry, because you had dinner," Heller said. "Assess what triggers that foray into the kitchen and create a game plan for managing it."
Some strategies: Have a glass of water or herbal tea, or engage in another activity, such as reading, taking a walk, or listening to music or an audiobook.
"Closing the kitchen after dinner is an easy way to shave off some pounds and get a better night's sleep," Heller said.
The findings were published online June 11 in the Journal of Clinical Endocrinology & Metabolism.
To learn more about obesity prevention, visit the U.S. Centers for Disease Control and Prevention .