Dieters looking to shed more fat and feel less hungry while they do it may benefit from a few more hours in bed, according to a new study.
Dieters lost the same amount of weight whether they slept for a full night or fewer hours, but those who got more sleep lost more fat and they also felt less hungry while awake, according to the study, which appears in the October 5 issue of the Annals of Internal Medicine.
"If your goal is to lose fat, skipping sleep is like poking sticks in your bicycle wheels," said Plamen Penev, an assistant professor of medicine at the University of Chicago and the director of the study.
"Cutting back on sleep, a behaviour that is ubiquitous in modern society, appears to compromise efforts to lose fat through dieting. In our study it reduced fat loss by 55 per cent," Penev added.
The study, undertaken by the University of Chicago's General Clinical Resource Center, tracked 10 overweight but healthy volunteers aged 35 to 49.
The participants had body mass indexes ranging from 25, which is considered overweight, to 32, which is considered obese.
Each ate a diet designed to give them 90 per cent of the calories they needed to maintain their weight without exercise and then spent 14 days getting up to 8.5 hours of sleep and another 14 days getting up to 5.5 hours of sleep. The difference between the two periods was pronounced.
When the dieters got up to 8.5 hours of sleep a day, more than half of the weight they lost was fat. When they were sleeping just 5.5 hours a day, only one-fourth of the weight loss was fat with the rest being mostly muscle tissue.
And getting less sleep also made it harder to diet, as the levels of ghrelin, a hormone that triggers hunger, increased when the volunteers were sleeping fewer hours.
The strictly controlled diets available to the participants meant they had no access to additional food even when their lack of sleep made them hungrier.
But that would not be the case for real-world dieters, who could further dent their chances of shedding fat by failing to sleep enough, feeling more hungry and eating additional calories.
Penev said the message of the study was clear. "For the first time, we have evidence that the amount of sleep makes a big difference on the results of dietary intervention," he said. "One should not ignore the way they sleep when going on a diet. Obtaining adequate sleep may enhance the beneficial effects of a diet."