If you are healthy and go to bed late regularly and you do not sleep enough, your risk of gaining weight is significantly greater than if you go to bed earlier and have a good night’s sleep every night, says a new study published in the journal Sleep.

If you also eat late at night, you will probably put on even more weight, researchers from the University of Pennsylvania added. In fact, they say it is the extra eating among sleep-deprived individuals that appears to be the main reason for the weight gain.

The authors say that theirs is the largest study so far of healthy people, under controlled laboratory conditions, that demonstrates a clear association between very late night sleeping combined with sleep restriction and weight gain.

Andrea Spaeth and team had one group of participants sleeping just from 4 a.m. to 8 a.m. each night for five nights running, and compared them to a control group who were in bed from 10 p.m. to 8 a.m.

The investigators also found that those who slept much less consumed more food, and therefore calories, compared to the normal-hours sleepers. Meals eaten during the late-night hours had a higher overall fat content than the other meals.

Sleep Lead author, Andrea Spaeth, a doctoral candidate in the psychology department at the University of Pennsylvania, said:

“Although previous epidemiological studies have suggested an association between short sleep duration and weight gain/obesity, we were surprised to observe significant weight gain during an in-laboratory study.”

The experiment was conducted at the Sleep and Chronobiology Laboratory at the Hospital of the University of Pennsylvania. It involved 225 people aged between 22 and 50 years, all of them healthy and non-obese. They were randomly selected either into the sleep restriction group or control group, and stayed in the lab for up to 18 days.

The participants were all served set meals at the same time each day. They also had free, 24-hour access to a well-stocked kitchen. They were allowed to move around, but not to exercise. They could play video games, watch TV, read and do other sedentary activities.

The study also showed that when sleep-deprived for several consecutive days:

  • Men put on more weight than women
  • African-Americans piled on the pounds more rapidly than Caucasians


Spaeth said:

“Among sleep-restricted subjects, there were also significant gender and race differences in weight gain. African Americans, who are at greater risk for obesityand more likely to be habitual short sleepers, may be more susceptible to weight gain in response to sleep restriction. Future studies should focus on identifying the behavioral and physiological mechanisms underlying this increased vulnerability.”

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