By Stephen Ornes

New work suggests sleep loss can affect how the body uses energy later.

National Institutes of Health website

One day, about six hours before they went to bed, five young men and two young women checked in to a Colorado hospital for a scientific sleepover. They climbed into their beds and stayed there for four nights and three days while a team of researchers kept a careful watch. The scientists wanted to measure how much energy is used by a person who stays up all night.

So, on the third night, the seven participants stayed in their beds reading, watching movies, and talking — in short, doing anything but sleeping.

In this experiment, scientists observed that a sleeping body conserved 161 calories. Or, thinking about it in another way, a person who stays up all night uses 161 calories more than if she were sleeping. In food terms, 161 calories is about a banana and a half, a slice of thin-crust cheese pizza, or a hot dog bun. In terms of exercise, it takes about 161 calories to mow the lawn for 30 minutes, bowl for an hour, or canoe for 40 minutes.

This study is the first time scientists have precisely measured the amount of energy the body uses over a 24-hour period.

So if the human body burns more calories while awake than while asleep, why not just stay awake to lose weight fast? Actually, such a weight-loss plan would backfire: Previous studies connect long-term sleep deprivation to obesity, which is the condition of being very overweight, and to other dangerous health problems.

After being kept awake all night, the seven participants were allowed to recover and doze for eight hours. When the participants were recovering, however, their bodies burned about 28 fewer calories than they had during normal nights’ sleep — suggesting to the scientists that the body conserves energy when working to make up for lost sleep.

This also suggests that the body’s energy processes during normal sleep are different than those used during recovery. And the body, while recovering, doesn’t use as much energy as when it is well-rested. When people slept normally, they expended 96 more calories than they did on days when they were making up for lost sleep. So a night spent awake can cause the body to burn fewer calories — which could be a recipe for gaining weight.

The researchers suspect that when a person sleeps, his body uses energy to do important jobs — like making connections in the brain, regulating hormones and helping the body’s natural defense system. When a person stays awake, he takes energy away from those important functions, Kenneth Wright told Science News. “It’s not worth the cost.”

Wright, a physiologist at the University of Colorado at Boulder, worked on the study. A physiologist is a scientist who studies the biological processes — sleeping, eating, using energy, etc. — of living organisms.

The scientists measured sleep patterns and energy use of the participants by monitoring brain activity and tracking breathing patterns. By studying the exchange of oxygen and carbon dioxide as the people breathed, the researchers could chart energy usage.

Most people don’t stay up all night very often, unless they work the night shift or suffer from a sleep disorder. Next, Wright and his colleagues want to measure the energy cost of losing a few hours’ sleep over many nights — which might be a more common situation.

POWER WORDS (adapted from the Yahoo! Kids Dictionary)

calorie A way to measure the energy contained in food. When a person eats food, her body oxidizes the food and releases the calories. The calories in food provide the energy needed to keep a body running.

oxidation The process of combining something with oxygen.

hormones Substances produced by a tissue in the body and carried away by the bloodstream. These chemicals can help control activities like growth or energy usage.

metabolism The chemical processes occurring within a living cell or organism that are necessary for the maintenance of life.

obesity The condition of being obese; increased body weight caused by excessive accumulation of fat.

carbon dioxide A gas produced when you exhale. It has no color, no odor and does not burn. This gas is also produced from fire and when organic materials break down. CO₂ is used in food refrigeration, carbonated beverages, fire extinguishers, and aerosols.