They said getting too little sleep can result in chronic changes in the diet that can increase the risk of obesity, especially in girls.

Prior studies have shown that too little sleep can lead to weight gain, but the new findings show where the extra calories come from.

Increasing intake of fatty foods, which are typically high in calories, can increase the overall daily caloric intake, and if it happens routinely, it can lead to excess fat.

The demonstration of chronically altered dietary patterns in adolescents with shorter sleep provides insight into why shorter sleep has been associated with obesity in prior experimental and observational studies, said Dr. Susan Redline of Brigham and Women's Hospital and Beth Israel Deaconess Medical Center in Boston, whose study appears in the journal Sleep.

Redline and colleagues studied 240 teenagers aged 16 to 19 taking part in an ongoing sleep study. Their sleep was monitored at home by a wrist band device and food intake was measured with interviews done by trained staff.

They found that teenagers who slept less than eight hours on weeknights consumed 2.2 percent more calories from fats and 3.0 percent fewer calories from carbohydrates than teenagers who slept eight hours or more.

The relative increase in fat consumption among shorter sleepers by 2.2 percent per day chronically may contribute to cumulative increases in energy consumption that would be expected to increase risk for obesity and cardiovascular disease, Redline said in a statement.

But the risk may be easily reversed.

The team found that each added hour of sleep lowered the odds of eating a high amount of calories from snacks by an average of 21 percent.

Curiously, when they looked by gender, they found the results were statistically significant in girls, but not boys.

While it is not clear why, the team said it may be that teenage girls are more likely to turn to food for emotional reasons than boys, but that needs to be studied.

Only 34 percent of the teenagers in the study slept for an average of eight hours or more. According to the American Academy of Sleep Medicine, teenagers need at least 9 hours of sleep to feel alert and rested.

Medicine Weight loss