Is there a good time of day to eat anything you like? Anything at all? Possibly, yes. The answer is based upon how our body is influenced by our daily rhythms of eating and sleeping. For example, numerous studies have shown that shiftwork and the odd patterns of sleeping and waking that this lifestyle involves, has many negative health consequences, including obesity, diabetes and metabolic syndrome as well as insomnia. Very little is known about how alterations in the rhythms of eating and sleeping affect overall health.

Scientists at the Salk Institute for Biological Studies in California recently published a study in the journal Cell Metabolism that investigated one important aspect of this problem. Their question: which is more important—what you eat or when you eat? For example, what would happen if you could only eat between the hours of 9 am and 4 pm? Would you gain less weight and be healthier overall even if you ate a high fat diet? Their answer was “yes.”

Mice were given free access to either a standard, nutritionally-balanced chow or a chow that was high (61% of calories) in fat. Some mice were allowed total access to the food at all times. Some mice were only allowed access to their assigned diet for an eight hour window during the early phase of their normal active period. As anyone would have predicted, the mice given total all-day access to a high fat diet (the standard American diet) developed obesity, diabetes, and metabolic syndrome and altered sleep-wake rhythms. According to the Centers for Disease Control one-third of Americans are obese, twenty-seven percent of older adults have diabetes and twenty-five percent report insomnia or other sleep problems.

Now for the good news! Mice that had time-restricted access to a high fat diet were significantly healthier than the mice given all-day access to the same diet. They lost body fat, had normal glucose tolerance, reduced serum cholesterol, increased bile acid production, improved motor function and normal sleep cycles. Most surprising, the daily caloric intake of all groups did not differ, regardless of their diet or feeding schedule.

Most of us have a short fasting period, i.e. we stop eating only we’re sleeping; and a long feeding window, i.e. we eat all day long. This feeding pattern is very unhealthy for both mice and humans; the CDC statistics agree. The take home message from this study: eat early and eat whatever you like but skip dinner and never have late night snacks.

© Gary L. Wenk, Ph.D., author of Your Brain on Food (Oxford, 2010)

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