The best path to a healthy weight may be a good night's sleep.
For years, researchers have known that adults who sleep less than five or six hours a night are at higher risk of being overweight. Among children, sleeping less than 10 hours a night is associated with weight gain.
Now a fascinating new study shows that losing just a few hours of sleep a few nights in a row can lead to almost immediate weight gain.
Sleep researchers from the University of Colorado recruited 16 healthy men and women for a two-week experiment, tracking sleep, metabolism and eating habits.
The subjects stayed in a special room where researchers tracked their metabolism by measuring the amount of oxygen they used and carbon dioxide they produced. Every bite of food was recorded, and strict sleep schedules were imposed.
The goal was to determine the effects of inadequate sleep over just one week - similar to what might occur when students cram for exams or office workers stay up late to meet a deadline.
During the first week, half the people were allowed to sleep nine hours a night while the other half stayed up to midnight and then slept five hours. Everyone had unlimited access to food. In the second week, the subjects swapped around.
The researchers found that those who stayed up late actually burned an extra 111 calories a day. But they ate far more than those who got nine hours of sleep.
They also ate more carbohydrates and their eating patterns changed - they ate less at breakfast and more after dinner. After a week, they gained an average of one kilogram.
During the second week, members of the group that had originally slept nine hours also gained weight when they were restricted to just five hours. And the other group began to lose some - but not all - of the weight gained in that first sleep-deprived week. New York Times