All-Nighters Make Bodies Hoard Calories

All-Nighters Make Bodies Hoard Calories

All-Nighters Make Bodies Hoard Calories






Recently, scientists had dismissed energy conservation as sleep’s most important mission. “Sure, there’s energy savings, but it’s not worth much. It’s a hot dog bun or a cup of milk’s worth,” Shaw says of many scientists’ attitude toward the amount of calories the body saves during sleep. But “small differences can have large consequences,” says Shaw, who was not involved in the current research.

Wright notes that eating just 50 extra calories per day over an extended period can lead to obesity. So, he contends, the amounts of energy savings associated with sleep aren’t trivial. But would-be dieters shouldn’t interpret the new data as pointing to sleep deprivation as a weight-loss plan, Wright says. Many studies have linked chronic sleep deprivation with obesity and other health problems (SN: 10/24/09, p. 28).

After staying up all night, volunteers burned about 28 fewer calories during eight hours of recovery sleep than they had during a full night of regular sleep. And the energy conservation didn't stop there. In the 24-hour period during which people caught up on missing sleep, they burned about 228 fewer calories than during a comparable period in which they were sleep-deprived. Overall, when people slept normally, they expended 96 more calories than they did on days when they were making up for lost sleep.

Volunteers were limited to eight hours of recovery sleep, and the effect might have been even greater if the researchers had allowed volunteers to fully sleep off their sleep debt, Wright says.

Shutting down muscles and other body functions during sleep might save the body even more energy than measured, but the body does have crucial energy requirements in other areas. The body may be using energy to fuel essential sleep functions such as rewiring connections between brain cells, boosting the immune system and regulating hormones, the researchers speculate. Sleep-deprived people are diverting some of the energy needed for those important processes, says Wright. “It's not worth the cost.”

Chronic sleep deprivation caused by conditions like sleep apnea and insomnia might exact a high energetic toll, Wright says. Each time volunteers awakened from sleep at night, energy consumption shot up, even if the episode lasted only seconds, the researchers report. People with sleep apnea rouse many times during the night, raising the possibility that they are tapping energy reserves needed for sleep’s other functions, Wright says.

Next, the researchers hope to learn whether missing a few hours of sleep each night over several days has different energy costs than staying up all night.

Image: Flickr/vibrant_art

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