Check Up: Study seeks new insight on sleep and diet

A new study by University of Pennsylvania researchers suggests that a good night's sleep and a good diet go hand in hand, but it also contains some perplexing data that raises more questions than it answers.

"I can't tell people what to do yet," said Michael Grandner, a psychologist and sleep researcher at Penn's Center for Sleep and Circadian Neurobiology.

The study he led, published online in the journal Appetite, examined the relationship between how much and what people ate and how long they slept. Eventually Grandner hopes to show whether changing your diet will make you sleep better or whether spending more time in bed will help you eat better.

"This is kind of the first step," he said.

Previous studies have shown that hunger for high-fat, high-carbohydrate foods increased when sleep was restricted. People who sleep less than the "normal" seven to eight hours a night also are at higher risk for obesity, diabetes, and heart and mental health problems. The risk increases the less people sleep, Grandner said. Sleeping too much is also associated with poor physical and mental health.

Using self-reported data from the National Health and Nutrition Examination Survey, the Penn team compared the diets of very short sleepers (less than five hours a night), short sleepers (five to six hours a night) and long sleepers (more than nine hours) with normal sleepers.

Some results were surprising. The very short sleepers, who were the heaviest, didn't eat the most calories. That was the short sleepers. Possible explanations, Grandner said, are that very short sleepers underreported how much they were eating or that lack of sleep "fundamentally disrupts the way the body regulates energy."

The normal sleepers had the most varied diets and managed not to eat less of any important nutrients than the other groups in the process. The very short sleepers had the least varied diets.

Grandner expected clear patterns from very short to short to normal to long sleeping. But that often was not the case. The very short and short sleepers sometimes looked quite different. Grandner, who has been studying short sleepers in the lab, found that interesting. He thinks risks for short sleepers are mixed and that they should be studied separately.

How were the diets different? The very short sleepers reported drinking less water and eating fewer foods rich in lycopene (from tomatoes and fruits) and carbohydrates. The short sleepers consumed less vitamin C, water, and selenium (this is in nuts, meat, and shellfish) and more lutein (found in green leafy vegetables). The longer sleepers consumed less carbohydrates and more alcohol.

Caffeine intake wasn't a significant factor.

For now, Grandner said, the important message is that "sleep is critical for health. We know this." So is diet, and the two are connected. Somehow.

Grandner said this region is particularly rich in sleep experts who can help. "If someone's having trouble sleeping," he said, "they shouldn't ignore it."