Mounting scientific evidence supports the notion that sleep deprivation significantly increases the risk for becoming overweight or obese. While the reasons for this phenomenon aren't entirely clear, experts have several theories.
One theory is that sleep loss produces changes in the body that ultimately lead to an increase in food consumption. Over the past decade, several studies have shown that sleep restriction suppresses blood levels of the appetite-suppressing hormone leptin, while increasing levels of ghrelin, a hormone that stimulates hunger.
In a scientific investigation conducted at the University of Chicago, researchers confirmed that one of the first consequences of sleep restriction is a dramatic boost in appetite. Volunteers who slept only four hours nightly for two nights were found to have a 24 percent increase in appetite.
The sleep-deprived subjects reported feeling significantly hungrier, and they weren't in the mood for grilled chicken and salads. The foods they craved most were those loaded with calories and carbohydrates, including candy, cookies, chips, bread and pasta.
After just two days of sleep restriction, blood tests performed on the subjects revealed an 18 percent reduction in appetite-suppressing leptin levels and a 28 percent increase in appetite-boosting ghrelin levels. The researchers concluded that these hormonal fluctuations, prompted by lack of sufficient sleep, stimulate hunger and trigger a strong preference for carbohydrate-rich foods.
Some scientists speculate that the impact of sleep loss on weight gain has more to do with alterations in a person's energy expenditure than with changes in appetite and calorie consumption. Sleep deprivation may slow the basal metabolic rate, the number of calories burned by the body while at rest.
Missing out on necessary slumber appears to influence a process known as non-exercise activity thermogenesis, or NEAT, which refers to calories burned during fidgeting, maintenance of posture and other physical activities of daily life. Scientific evidence suggests that people who spend less time sleeping at night may also spend less time moving around during the day, thus expending fewer calories than they would if they were well-rested.
Whether sleep loss causes folks to eat more or move less, there's little doubt that it ultimately leads to weight gain. Researchers investigating the link between sleep duration and weight status analyzed data collected from nearly 70,000 middle-age women enrolled in the Nurses' Health Study over a 16-year period.
The scientists found that women who regularly slept for five hours or less each night not only weighed more at the beginning of the study, they also tended to gain significantly more weight over time. Compared to women who habitually slept at least seven hours a night, these short-sleeping women were 32 percent more likely to experience a major weight gain, defined as an increase of 33 pounds or more, and they were 15 percent more likely to become obese.
Getting just one extra hour of sleep each night was beneficial in terms of preventing weight gain and obesity. Compared to women who regularly slept at least seven hours nightly, those who routinely slept six hours a night had a 12 percent greater chance of experiencing a major weight gain and a 6 percent greater chance of becoming obese.
The link between weight gain and sleep is supported by other epidemiologic data. Over the last 40 years, American adults have cut their average sleep time by nearly two hours.
In 1960, U.S. adults slept an average of 8.5 hours a night. By 2002, most were sleeping less than seven hours nightly.
As sleep duration has fallen, the average weight has risen. In 1960, only a quarter of adults were overweight, and obesity was practically nonexistent. Today, more than two-thirds of American adults are overweight, and nearly one in three is obese.
The good news is that for most folks who are short on slumber, there's a simple solution: spend more time sleeping. For those who have trouble falling or staying asleep, it's wise to enlist the help of a physician.
If weight loss is your goal, watching what you eat is still mandatory. And although it may seem too good to be true, hitting the sack may be just as important as hitting the gym.
Rallie McAllister is a board-certified family physician, speaker and the author of several books, including "Healthy Lunchbox: The Working Mom's Guide to Keeping You and Your Kids Trim." Her website is www.rallieonhealth.com.