Keen Cuisine: The Sandman Dineth

Crinkle of plastic wrap, wet thud of the ice cream box hitting the kitchen counter, incandescent refrigerator
glow made eerie in a dim kitchen. The sights and sounds of sleeplessness are familiar to many Americans, and scientific evidence now indicates that bad diets and bad sleep perpetuate each other.

On the one hand, lack of sleep throws appetite hormones into disarray—and also causes us to make poor food decisions. "There's a critical mass of evidence that we need to help people sleep better to help them lose weight," says Christopher Gardner, a nutritionist at Stanford University. After a four-hour night's sleep, people are more likely to choose convenient junk food, a study at the University of Pennsylvania found.

Other studies have shown that we consume more calories after a few consecutive nights of poor sleep because of changes in appetite-regulating hormones. Ghrelin, which signals hunger, increases, while leptin, which suppresses appetite, decreases. As a result, the brain tells the body to keep eating. On top of that, sleep-deprived people exercise less and don't burn off the extra calories.

Poor eating then drives poor sleeping. In a recently unveiled pathway, cellular fat digestion pushes back the body's time-for-bed signal: Metabolic processes partly control our internal circadian clocks. A study published in the journal Cell Metabolism showed that mice fed a high-fat diet stayed up nibbling, while mice on a normal diet slept soundly.

It's wise to avoid food high in protein or fat within three hours of hitting the sack, because the system has to work harder to digest them. The discomfort of going to bed on an empty stomach can inhibit sleep, too. So if you're hungry, it's best to munch on good old-fashioned comfort foods made of complex carbs.

The notion that eating past a certain hour will make you fat is a myth; just look at the late diners of Spain and Italy. But experts do push portion control, recommending a snack of 150 calories, which is a scoop of low-fat ice cream or a couple of rice cakes. When it comes to weight gain, the real problem isn't the time of day but the amount of food—especially fats—a person eats, says George Blackburn, the director of the Center for the Study of Nutrition and Medicine at Harvard.

As for the idea of warm milk, or tryptophans, putting you down, the science isn't there, but Blackburn takes a "whatever works" approach. "If warm milk helps you relax before bed, who cares if it's a rabbit's foot?"