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Late nights and less sleep may lead to weight gain

Night owls take note: your late-night habits may be increasing your chance of gaining weight, with research showing that late bedtimes and less sleep can lead to higher calorie intake.

BMJ Group News

What do we know already?


Several studies have suggested that a lack of sleep can increase the chance of weight gain and obesity. How sleep might affect weight isn’t entirely clear. Some studies have shown that a lack of sleep affects hormones that help control our appetite. Others have suggested that people eat more calories to make up for the tiring effects of lost sleep, and that people who stay up late tend to sleep less overall and eat more calories during their extended waking hours.

However, these are mostly theories, as few good-quality studies have explored the link between sleep, eating, and weight gain. To help fill this gap in what we know, researchers recruited 225 healthy, non-obese people (aged 22 to 50 years old) to live in a sleep laboratory for 12 to 18 days. They randomly selected participants to have five nights of either:

  • Restricted sleep, which meant they spent four hours in bed, from 4 a.m. to 8 a.m., or
  • Unrestricted sleep, which meant they spent 10 hours in bed, from 10 p.m. to 8 a.m.

During the day, people had regular meals and could also eat at other times, as food was always available in the kitchen. What food they ate and their weight were closely monitored, so the researchers could compare the two groups to see whether restricted sleep increased the chance of weight gain. The researchers also tracked how many calories a smaller group of people consumed each day.

What does the new study say?

People with restricted sleep ate more calories than those with unrestricted sleep. Interestingly, all of these extra calories (around 550, on average) were from food consumed between 10 p.m. and 4 a.m. When eating late at night, people also got more of their calories from fat than at other times of the day.

On average, people with restricted sleep gained nearly a kilogram of weight during the study, while those with unrestricted sleep gained only one-tenth of a kilogram.

How reliable is the research?

These findings should be reliable, as this was a good-quality study. However, it’s worth noting that the study only included people who were healthy, fairly young, and not obese. So it’s not clear whether these findings apply to other groups of people. Also, the participants weren’t able to exercise during the study and might not have had access to all the foods they usually ate. These things might have had an effect on the findings.

The study was also fairly short. So it can’t tell us how late nights and less sleep might affect a person’s weight over a long period.

What does this mean for me?

This study provides good evidence that restricted sleep can increase how many calories people eat and lead to weight gain, at least in the short term. If you tend to stay up late and get little sleep, these findings may be especially pertinent to you, as after 10 p.m. was when people typically got their extra calories, rather than during the day.

Most people need between six and eight hours of sleep a night. If you have trouble falling asleep or staying asleep, you can speak to your doctor about ways to make sure you get the sleep you need.

Published on July 03, 2013

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