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When it comes to weight loss, when you eat might be as important as what you eat.

Scientists at the Salk Institute for Biological Studies found that mice limited to eating during an 8-hour period are healthier than mice that eat freely throughout the day, regardless of the quality and content of their diet.

"Our findings suggest that regular eating times and fasting for a significant number of hours a day might be beneficial to our health," says Satchidananda Panda, an associate professor in the Regulatory Biology Laboratory and senior author of the paper.

In an attempt to determine whether obesity and metabolic diseases result from a high-fat diet or from disruption of metabolic cycles, Panda's team conducted an experiment with mice.

The team put groups of mice, which had the same genes, gender and age, on different eating regimens. Animals in two of the groups dined on high-fat, high-calorie chow (like eating potato chips and ice-cream for all your meals). Half of them could eat whenever they wanted and nibbled on and off throughout the night and day. The other mice had access to food only for eight hours at night, when they were most active. Two control groups ate a standard diet under similar conditions.

After 100 days, the mice who ate fatty food frequently throughout the day gained weight and developed high cholesterol, high blood glucose, liver damage and diminished motor control, while the mice in the time-restricted feeding group weighed 28 percent less and showed no adverse health effects despite consuming the same amount of calories from the same fatty food. Moreover, the time-restricted mice outperformed the ad lib eaters and those on a normal diet when given an exercise test.

"This was a surprising result," says Megumi Hatori, a postdoctoral researcher in Panda's laboratory and a first author of the study. "For the last 50 years, we have been told to reduce our calories from fat and to eat smaller meals and snacks throughout the day. We found, however, that fasting time is important. By eating in a time-restricted fashion, you can still resist the damaging effects of a high-fat diet, and we did not find any adverse effects of time-restricted eating when eating healthy food."

Hatori cautioned that people should not conclude that eating lots of unhealthy food is alright as long as they fast. "What we showed is under daily fasting the body can fight unhealthy food to a significant extent," she says. "But there are bound to be limits."

"The take-home message," says Panda, "is that eating at regular times during the day and overnight fasting may prove to be beneficial, but, we will have to wait for human studies to prove this."

The paper was published in Cell Metabolism.