Late bedtimes and less sleep may lead you to gain weight

Going to bed late and getting less sleep may lead healthy people to pile on the pounds, a new study has warned.
US researchers found that healthy adults with late bedtimes and chronic sleep restriction may be more susceptible to weight gain due to the increased consumption of calories during late-night hours.
The study was conducted in the Sleep and Chronobiology Laboratory at the Hospital of the University of Pennsylvania. The study group comprised 225 healthy, non-obese individuals, ranging in age from 22-50 years.
Subjects were randomised to either the sleep restriction or control condition and spent up to 18 consecutive days in the laboratory.

Results showed that sleep-restricted subjects who spent only four hours in bed from 4 am to 8 am for five consecutive nights gained more weight than control subjects who were in bed for 10 hours each night from 10 pm to 8 am.
The study found an overall increase in caloric intake during sleep restriction, which was due to an increase in the number of meals consumed during the late-night period of additional wakefulness.

Furthermore, the proportion of calories consumed from fat was higher during late-night hours than at other times of day.
"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," said lead author Andrea Spaeth.

The study also found that during sleep restriction males gained more weight than females, and African Americans gained more weight than Caucasians.
The study will be published in the journal Sleep.