In addition to fruitcake, eggnog and alcohol, sleeplessness can be added to the list of factors that may cause you to pack on a few pounds this holiday season.
Researchers from the University of Chicago and Stanford University have completed two studies that show lack of sleep causes changes in hormones that result in increased appetite and weight gain.
Scientists were amazed to find that hormone levels can be affected after as few as two nights of poor sleep, triggering alterations in the brain's chemistry that increase appetite.
These findings have been greeted with enthusiasm from sleep and diet experts, who consider them potentially groundbreaking in terms of changing the way they counsel patients on obesity.
"There is no question when you look at these two studies, we are definitely onto something," said Dr. Emmanuel Mignot, who headed the Stanford study. "What it should tell people is that those who are considering losing weight should think of healthy sleeping habits in the same sentence as healthy eating habits and good exercise habits."
The two studies used different approaches to arrive at the same conclusion.
The group from Chicago, led by Eve Van Cauter, asked a small group of men in their 20s to restrict their sleep to four hours for two consecutive nights. They were then allowed to sleep for 10 hours the next two nights.
Van Cauter found not only that the men had a 24 percent greater appetite after the two nights of sleep deprivation, but they specifically craved high-sugar, high-salt and starchy foods.
In addition, analysis of their blood after the two nights of poor sleep found lower levels of leptin, a hormone that suppresses appetite, and higher levels of ghrelin, a hormone that triggers hunger.
Mignot's group looked at the sleep patterns of more than 1,000 individuals from Wisconsin and found that the less people slept, the higher their body mass index, a value that is often used to measure body fat. Results show that individuals who sleep less than eight hours a night on average are heavier than those who get a full night's rest.
The researchers also found that patients who averaged five or fewer hours of sleep per night had the same changes in leptin and ghrelin as those in the Chicago study.
Mignot found there were no significant differences between males and females in the way sleeplessness affected hormone levels or body weight.
Most physicians who have reviewed the studies agree that the findings may signal a new approach to combating obesity.
"There are plenty of reasons to get enough sleep, but this one might motivate people, especially if there is a real hormonal effect that shows getting enough sleep helps control weight," said Dr. Keith-Thomas Ayoub, associate professor of pediatrics at Albert Einstein College of Medicine in New York. "It might help people feel less blame and might help motivate them to take steps that avoid setting themselves up to fail."
However, many experts caution that simply increasing the amount of sleep each night is unlikely to result in significant weight loss unless patients also commit themselves to a healthy lifestyle.