18 May 2012

Eating Schedule and Biological Clock Important Factor In Obesity

The human body follows a daily schedule when it comes to its regular internal functions. This biological clock is based on a 24 hour time period and is heavily influenced by light.

This schedule is also known as the circadian rhythm. It covers any biological process which displays an endogenous, entrainable oscillation of one day or about 24 hours and is widely observed in living organisms like plants, animals and even in fungi and certain bacterium.

Circadian rhythms are internally scheduled but can be adjusted to the local environment. The most common and most important influencing adjusting factor is daylight.

Common processes influenced by the circadian rhythm are hunger, bowel movement, and sleeping and waking hours. Not all biological functions follow or are considered circadian in nature. For it to be circadian, the process should be repeated once every 24 hours, it should not be influenced by external factors (endogenous), the process is aligned to a schedule (entrainable), and that the process still holds true despite changing temperature conditions.

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. That's the conclusion of a study reported in the Cell Press journal Cell Metabolism published early online on May 17th.

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.

Video: Planning A Good Diet

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."


Cell Press
Cell Metabolism
Salk Institute for Biological Studies
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