Failure to get a full night's sleep can lead to weight gain or compromise the beneficial effects of a reduced calorie diet on total body fat, according to presentations at SLEEP 2009, the annual meeting of the Associated Professional Sleep Societies, underway this week in Seattle.

Reduced sleep duration has become a common aspect of the westernized lifestyle, defined by physical inactivity and overeating, Dr. Plamen Penev, from the University of Chicago, told Reuters Health. Diet-induced weight loss is a major behavioral strategy for metabolic risk reduction. However, whether it is effective during times of reduced sleep duration is unknown.

Penev and his associates studied nine healthy overweight volunteers. The average subject age was 40 years and the average body mass index was 27.5, which is in the overweight range. The subjects completed two 14-day trials, conducted at least 3 months apart, during which time they spent either 5.5 hours or 8.5 hours in bed per night.

During both study periods, they consumed a nutritionally balanced diet containing calories up to 90 percent of their resting metabolic rate. Weight loss during each trial was similar (6.6 vs 6.4 lbs), respectively).

However, fat represented only 26 percent of the weight loss during periods of sleep restriction compared with 57 percent during the 8.5-hour sleep intervals, indicating an increased loss of lean body mass occurred during reduced sleep conditions.

Penev and colleagues conclude that the neurologic and endocrine system's response to the reduced calorie diet was amplified by recurrent sleep restriction, as evidenced by increased concentrations of ghrelin, a hormone reported to stimulate the appetite.

In another study conducted by Dr. Siobhan Banks and associates at the University of Pennsylvania in Philadelphia, 92 healthy adults (22 to 45 years old) spent 2 nights of unrestricted sleep (10 hours in bed), followed by 5 nights of restricted sleep (4 hours in bed), and then 4 nights of recovery. Nine control subjects spent 10 hours per night in bed during the 11-day study.

Sleep-restricted subjects experienced an average weight gain of 2.9 lbs. during the trial protocol, even though they reported decreases in appetite, food cravings and food consumption. By contrast, there was no significant weight gain in the control group.

In a prepared statement, Banks, currently at the University of South Australia, noted that During real-world periods of sleep restriction...keeping up regular exercise is just as important as what food you eat.