Can't sleep? Eat less to stay mentally sharper

Staying up too late and eating too much just seem to go together.

But two new studies from the University of Pennsylvania suggest sleep deprivation and food are a bad combination for your brain and your waistline.

One found that eating less at night after inadequate sleep helped study subjects function better mentally than if they had eaten more. The other found that metabolic rates slowed in people who had gotten too little sleep for several days. The change was particularly troubling for African Americans, who had slower metabolisms to begin with. This may be one reason short sleepers are prone to obesity.

Both studies were presented last week at the annual meeting of Associated Professional Sleep Societies, known as SLEEP. A third Penn study examined the relationship between different types of exercise and sleep quality.

For the mental-functioning study, 44 subjects were given unlimited access to food and drink, but not sleep, for three days. They were allowed to sleep between 4 and 8 a.m. On the fourth night, they also got four hours of sleep, but 20 participants continued to eat and drink as they wished and 24 got only water after 10 p.m.

During that fourth night, the fasters performed better on tests of reaction time and attention than the eaters.

There were no differences between the two groups in working memory or information processing speed, or in their ratings of their sleepiness, stress, and mood.

Rates on all measures declined during the first three days. For the alertness test, study subjects were asked to respond when they saw a target appear on a computer screen. On the first night, they averaged two errors in 10 minutes. On the fourth night, the fasters made four mistakes. The eaters made eight.

People in the study ate an extra 500 calories per day after 10 p.m., said lead author Andrea Spaeth. Previous work had shown they needed only an extra 100.

David Dinges, chief of Penn's division of sleep and chronobiology, the paper's senior author, said researchers did not yet know why people tend to eat more when they sleep less, but sleep and circadian rhythms seem tied to metabolism and messages from the brain about eating.

In the study on metabolic rate, 36 adults got their usual amount of sleep for two nights. Then they were allowed only four hours of sleep for five nights, followed by one night with 12 hours of "recovery" sleep. A control group of 11 people got to spend 10 hours in bed each night for six nights.

The resting metabolic rate decreased in the experimental group after the five nights of short sleep.

The change was small, the equivalent of needing about 60 fewer calories a day.

"It will add up over time, though," said Namni Goel, a psychologist who led the metabolic study.

Dinges said more work needed to be done to develop "countermeasures" that might help chronically sleep-deprived people fight weight gain.

Though eating less obviously makes sense, it is equally obvious that that is hard to do, even for people who get plenty of sleep.

"It's not just willpower," he said. "There are biological responses . . . especially if you're sleep restricted, that seem to be overwhelming."

The study on exercise and sleep was led by Michael Grandner, who works in Penn's Center for Sleep and Circadian Neurobiology. Previous work has shown that exercise is associated with healthier sleep and that people who sleep less than seven hours a night are at risk for health problems.

This study looked at sleep and different types of physical activity involving nearly 430,000 adults in the 2013 Behavioral Risk Factor Surveillance System. The bad news for parents is that household work and child care increased the risk of getting insufficient sleep.

Those who got most of their exercise from walking had better sleep habits. More purposeful activities - aerobics, biking, gardening, golf, running, weightlifting, and yoga/Pilates - all were associated with even better sleep.

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@StaceyABurling