Carbs, junk food? Now add lack of sleep to the things that can make you fat

Sugar, carbs, fat--it’s hardly news that these are big contributors to all that unwanted weight.

Now add a fourth: lack of sleep.

According to a recent study by psychologists at the University of Pennsylvania, people who get less sleep at night are more likely to choose food the next day that will put on extra pounds.

“It’s possible people are less motivated to make healthy food choices when they’re really tired,” said Tony Wells, a graduate student who co-wrote the study with Dr. Dean Cruess of the department of psychology.

In the study, published this month in Psychology and Health, 50 undergraduates recorded their sleep hours and food intake over a period of four days, and researchers calculated the number of calories and fat and sugar content in the foods. The first night participants slept eight hours, the second night four hours or less.

Researchers found that on the following day, participants were less likely to choose food items because of health reasons--to control their weight or to eat nutritiously--than they were after eight hours of sleep. The sleepy students mainly chose foods based on convenience--whatever was easiest to prepare or buy.

Scientists still need to figure out why the change in food choice occurs. Some speculate that the reduced thinking capacity brought on by loss of sleep could lead people to choose junk food. Sleepy people may just put less effort into doing anything, including choosing their food.

In addition, if people lose enough sleep, all their energy may be spent trying to stay awake, and things like healthy diets might fall to the wayside.

“If a person has a major drive such as a need to sleep, they may focus on that one drive at the exclusion of others, such as getting more food,” Wells said.

Surprisingly, however, even though the study found that the sleep-deprived people made unhealthy choices, they tended to eat less of what food they chose. That is, when they did eat, they tended to eat unhealthy foods, but they ate less of them than they normally would.

As a result they ended up taking in fewer calories--about the equivalent of one McDonald’s hamburger.

The decrease in calories was an unexpected finding for scientists. Previous research had shown that sleep-deprived people got hungrier than good sleepers as their appetite-inducing hormones increased. They tend to chow down on comfort foods like fatty snacks. This led researchers to hypothesize that calorie intake would increase rather than decrease with loss of sleep.

Scientists were also surprised at the decrease in calorie intake after sleep loss because research had demonstrated a clear association between lack of sleep and obesity.

More than 13 large epidemiological studies have supported a link between short sleep and obesity--that is, people who sleep less are more likely to be overweight. Now scientists are trying to piece together this association with the recent study’s results of lowered calorie consumption.

Many researchers, however, are in disagreement as to why the calorie loss occurs. Dr. Emmanuel Mignot, who researches sleep and obesity at Stanford University Medical School, says it’s still possible to gain weight even if you’re eating fewer calories.

To gain weight, one has to have a net gain in calories, either by eating more calories or by burning fewer calories. Scientists had hypothesized that sleep-deprived people craved unhealthy foods, and therefore ate more junk food, causing them to gain weight.

But based on this recent study, Mignot says there’s another possibility: Sleep loss may slow the body’s ability to burn off the calories, so even if people eat less, they will burn so few calories they’ll still add on pounds.

“Sleep may change how you burn the calories you take in,” Mignot said. “It’s possible that a lack of sleep can slow metabolism, so sleepy people are unable to burn calories as fast.”

Body weight is so finely regulated that people tend to eat five to 10 times their weight in a year without gaining weight, Mignot said. The body constantly controls how much food is consumed and how many calories burned to keep weight steady.

But if someone who’s very tired burns the calories too slowly, even if they eat less they still may gain weight. Over time the person will gain pounds if the body burns calories too slowly for the amount of food taken in.

Other researchers agree with Mignot that sleep is a crucial factor in weight control, but for different reasons.

“It’s possible that if someone’s really tired, he or she may be really hungry and still not eat,” Wells said. Exhaustion may prevail over hungry tummies, resulting in tired people eating less even if they don’t want to.

Alternatively, a bad night of sleep may actually lead people to want to eat less, according to Dr. George Blackburn, associate director of the division of nutrition at Harvard Medical School.

This is because sleep loss is a stress on the body, he said, which triggers the body’s “fight or flight” response--a reaction to try to get rid of the stress. The result is a jittery nervousness that lessens the desire to eat.

“When you become sleep deprived, you lose your thinking capacity--you shipwreck yourself,” Blackburn said. “The main player is the thinking brain, which we’re not disputing is injured temporarily by sleep deprivation. You’ll be practicing away from your commonsense that healthy food keeps you healthy.”

Sleep deprivation can also trigger other risks, such as a compromised immune system, negative mood and, over time, an increased risk for diabetes and cardiovascular problems.

“Everyone knows exercise is good and eating badly is bad,” Mignot said. “We need to build up the evidence about the serious problems of sleep deprivation so that one day healthy sleep will be as important as exercise and dieting.”

E-mail: esr2107@columbia.edu