Cutting back on sleep can reduce the amount of fat loss when dieting, according to researchers form the University of Chicago.
“If your goal is to lose fat, skipping sleep is like poking sticks in your bicycle wheels,” said study director Plamen Penev, MD, PhD, assistant professor of medicine at the University of Chicago. “Cutting back on sleep, a behavior that is ubiquitous in modern society, appears to compromise efforts to lose fat through dieting. In our study it reduced fat loss by 55 percent.”
When dieters got adequate sleep, more than half of the weight they lost was fat. When they cut back on their sleep, only one-fourth of their weight loss came from fat. However, when dieters in the study got a full night’s sleep, they lost the same amount of weight as when they slept less.
When sleep was restricted, dieters produced higher levels of ghrelin, a hormone that triggers hunger and reduces energy expenditure. They also felt hungrier.
The study followed 10 overweight but healthy volunteers aged 35 to 49 with a body mass index ranging from 25, considered overweight, to 32, considered obese. Participants were placed on an individualized, balanced diet, with calories restricted to 90 percent of what each person needed to maintain his or her weight without exercise.
Each participant was studied twice: once for 14 days in the laboratory with an 8.5-hour period set aside for sleep, and once for 14 days with only 5.5 hours for sleep. They spent their waking hours engaged in home- or office-like work or leisure activities.
The volunteers lost an average of 6.6 pounds during each 14-day session. During weeks with adequate sleep, they lost 3.1 pounds of fat and 3.3 pounds of fat-free body mass, mostly protein. During the short-sleep weeks, participants lost an average of 1.3 pounds of fat and 5.3 pounds of fat-free mass.
Average levels of ghrelin did not change when dieters spent 8.5 hours in bed. When they spent 5.5 hours in bed, their ghrelin levels rose over two weeks from 75 ng/L to 84 ng/L.
Higher ghrelin levels have been shown to “reduce energy expenditure, stimulate hunger and food intake, promote retention of fat, and increase hepatic glucose production to support the availability of fuel to glucose dependent tissues,” the authors note. “In our experiment, sleep restriction was accompanied by a similar pattern of increased hunger and … reduced oxidation of fat.”
The message for people trying to lose weight is clear, Penev said. “For the first time, we have evidence that the amount of sleep makes a big difference on the results of dietary interventions. One should not ignore the way they sleep when going on a diet. Obtaining adequate sleep may enhance the beneficial effects of a diet. Not getting enough sleep could defeat the desired effects.”
University of Chicago