A new study has shown that cutting back on sleep reduces the benefits of dieting.
When dieters in the study got a full night's sleep, they lost the same amount of weight as when they slept less. When dieters got adequate sleep, however, 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.
They also felt hungrier. When sleep was restricted, dieters produced higher levels of ghrelin, a hormone that triggers hunger and reduces energy expenditure.
"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," said study director Plamen Penev, assistant professor of medicine at the University of Chicago.
The study, performed at the University of Chicago's General Clinical Resource Center, 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.
During the two-week, 8.5-hours-in-bed phase, volunteers slept an average of 7 hours and 25 minutes each night. In the 5.5-hour phase, they slept 5 hours and 14 minutes, or more than two hours less. The number of calories they consumed, about 1,450 per day, was kept the same.
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.
Getting adequate sleep also helped control the dieters' hunger. 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.
The study has been published in the Annals of Internal Medicine.