Eating less and exercising more to keep obesity at bay might not be enough. Now there is new evidence to show that eating at the right time is also a must for weight loss. A Northwestern University study has found that eating at irregular times, especially when the body wants to sleep, influences weight gain. "How or why a person gains weight is very complicated, but it clearly is not just calories in and calories out," said Fred Turek, neurobiology and physiology professor at the Weinberg College of Arts and Sciences and director of the Centre for Sleep and Circadian Biology. The findings could have implications for developing strategies to combat obesity in humans, as the US and the world battle what has been called an "obesity epidemic". More than 300 million adults worldwide are obese, including more than a third of American adults. "Their schedules force them to eat at times that conflict with their natural body rhythms. This was one piece of evidence that got us thinking -- eating at the wrong time might be contributing to weight gain," says Arble. Simply modifying the time of feeding alone can greatly affect body weight, the researchers found, says a university statement. Mice that were fed a high-fat diet during normal sleeping hours gained significantly more weight (a 48 percent increase) than mice eating the same type and amount of food during naturally wakeful hours (a 20 percent increase).