Research suggests eating only during a nine- to 12-hour time period can help maintain healthy weight

For a long time, scientists supposed that eating after midnight was unhealthy, but now a study has provided support for the notion. When scientists prevented mice from eating whenever they wanted, the animals avoided obesity and metabolic issues—even when the diet was unhealthy, Ben Wiseman reports for The New York Times.

In a previous study, researchers at Salk Institute for Biological Studies in San Diego began studying mice eating patterns. The mice in the study that were permitted to eat whenever they wished gained weight and became unwell, while the mice who were only permitted to eat during an eight-hour window didn’t gain much weight or develop metabolic problems.

The new study, which was published in the journal Cell Metabolism in December, Salk scientists provided groups of mice with one of four diets: high-fat, high-fructose, high-fat and high-sucrose and regular mouse food. “Some of the mice in each dietary group were allowed eat whenever they wanted throughout their waking hours; others were restricted to feeding periods of nine, 12 or 15 hours,” Wiseman writes. The caloric intake for all the mice was the same.

Some of the mice in the time-restricted groups were allowed to eat whenever they wanted on weekends, and some of the eat-anytime mice were moved to the restricted groups halfway through the study. At the end of the study, the mice that ate whenever they pleased became obese and metabolically ill, but the time-restricted mice stayed healthy. The mice switched from the former group to the latter lost some of the weight they’d gained, Wiseman writes.

Though scientists don’t know exactly why eating during a designated timeframe helps prevent weight gain, Dr. Satchidananda Panda, who oversaw the studies, and his colleagues think it has to do with the body’s internal clock. “Meal times have more effect on circadian rhythm than dark and light cycles,” Panda said. Circadian rhythm influences the function of many genes in the body that have to do with metabolism.

These studies have only been performed using mice, but Panda believes the results could apply to humans. He suggests that people only eat within a 12 hour—or shorter—window each day. The clock begins with the first thing a person eats in the morning. (Read more)