THURSDAY, Jan. 20 (HealthDay News) -- Skipping a night of sleep is equivalent of the amount of energy it would take to walk about two miles, new research suggests.

Alternatively, looked at in terms of food, a night of sleep deprivation can be translated into losing about 135 calories -- about the amount found in two slices of bread or a nearly eight ounces of semi-skimmed milk.

"While the amount of energy saved during sleep may seem small, it was actually more than we expected," study author Professor Kenneth Wright, director of Colorado University's Sleep and Chronobiology Laboratory, said in a news release.

"[And] if one considers the amount of positive energy storage needed to explain the obesity epidemic is 50 calories a day, the energy savings represented by sleep is physiologically meaningful," he added.

Wright and his colleagues report their findings in the current issue of the The Journal of Physiology.

The team's results are based on work with seven young adults who were tracked while they spent three days in bed while placed on a weight maintenance diet.

While the participants slept a full eight hours on day one, on days two and three they were deprived of sleep for a total of 40 hours, after which they recovered with eight hours of sleep.

The authors found that over the course of 24 hours of sleep deprivation, the participants expended 7 percent more energy than they would during a normal night of sleep.

Wright and his associates said the finding suggests that the normal sleep-wake cycle is linked to a typical use of body energy, and that depriving the body of sleep appears to siphon off some of that energy.

On the other hand, the team said, the finding raised questions about why people don't save even more energy while asleep.

"There are other functions of sleep that are important and cost energy," Wright pointed out. "Some conserved energy may be re-distributed to support vital physiological processes, like learning and memory consolidation, immune function and hormone synthesis and release."

And, he cautioned, sleep deprivation should not be thought of as a means to lose weight, since prior research shows that a lack of sleep is linked to both cognitive impairment and weight gain.

More information

For more on sleep, visit the National Institute of Neurological Disorders and Stroke.