When You Eat Matters, Not Just What You Eat

When it comes to weight gain, when you eat might be at least as important as what you eat.

When mice on a high-fat diet are restricted to eating for eight hours per day, they eat just as much as those who can eat around the clock, yet they are protected against obesity and other metabolic ills, the new study shows. The discovery suggests that the health consequences of a poor diet might result in part from a mismatch between our body clocks and our eating schedules.

"Every organ has a clock," said lead author of the study Satchidananda Panda of the Salk Institute for Biological Studies. That means there are times that our livers, intestines, muscles, and other organs will work at peak efficiency and other times when they are—more or less—sleeping.

Those metabolic cycles are critical for processes from cholesterol breakdown to glucose production, and they should be primed to turn on when we eat and back off when we don't, or vice versa. When mice or people eat frequently throughout the day and night, it can throw off those normal metabolic cycles.

"When we eat randomly, those genes aren't on completely or off completely," Panda said. The principle is just like it is with sleep and waking, he explained. If we don't sleep well at night, we aren't completely awake during the day, and we work less efficiently as a consequence.

To find out whether restricted feeding alone—without a change in calorie intake—could prevent metabolic disease, Panda's team fed mice either a standard or high-fat diet with one of two types of food access: ad lib feeding or restricted access.

The time-restricted mice on a high-fat diet were protected from the adverse effects of a high-fat diet and showed improvements in their metabolic and physiological rhythms. They gained less weight and suffered less liver damage. The mice also had lower levels of inflammation, among other benefits.

Panda says there is reason to think our eating patterns have changed in recent years, as many people have greater access to food and reasons to stay up into the night, even if just to watch TV. And when people are awake, they tend to snack.

The findings suggest that restricted meal times might be an underappreciated lifestyle change to help people keep off the pounds. At the very least, the new evidence suggests that this is a factor in the obesity epidemic that should be given more careful consideration.

"The focus has been on what people eat," Panda said. "We don't collect data on when people eat."