The largest study of healthy people under controlled laboratory conditions was recently conducted at the University of Pennsylvania. The study included 225 people, ages 22-50. All were healthy and non-obese. Randomly selected into two groups, one group was restricted to sleeping from 4-8 a.m. while the other group slept from 10 pm to 8 am daily. All set meals were served at the same time each day and the participants had 24 hour access to a well-stocked kitchen. And although participants could not exercise, they could do many sedentary activities such as read and play video games.  The researchers were looking at causes of weight gain in healthy people.

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.”

Kenneth Wright, director of the Sleep and Chronobiology Laboratory explained that it is not just the less sleep that causes weight gain. When people sleep less they eat more.

Wright said “I don’t think extra sleep by itself is going to lead to weight loss. But I think it could help. If we can incorporate healthy sleep into weight-loss and weight-maintenance programs, our findings suggest that it may assist people to obtain a healthier weight.”