Preventing obesity may simply be a matter of time (of eating): Salk study

Obese people may be able to lose weight without drugs or altering their diet. Changing their mealtimes may do the trick, if a groundbreaking new study by Salk Institute and UC San Diego researchers holds up.

The time of eating appears to be a previously unrecognized key element in obesity, says the scientists, who performed the study in mice. Obesity appeared in mice allowed to eat a high-fat diet around the clock, but the same diet didn’t produce obesity if the mice were restricted to an eight-hour eating period.

The difference was huge; the eating time-restricted mice weighed 28 percent less than those allowed to eat around the clock, said Satchidananda Panda, a Salk associate professor and senior author of the study. And the eating-restricted mice had healthier livers, with less fat.

The study was published Thursday in the journal Cell Metabolism. Megumi Hatori, a postdoctoral researcher in Panda’s laboratory, is first author of the paper.

Metabolic similarities between mice and humans means the results probably have implications for our diets, the researchers say.

If so, medical science could get an entirely new tool to wield in the struggle against obesity, which keeps increasing despite decades of research on diets, and medications. Obesity is associated with illnesses including Type 2 diabetes, heart disease, and sleep apnea.

The total tab for obesity and related diseases comes to $190 billion a year in the United States, or 21 percent of all health spending, according to a study released earlier this year by health economists led by John Cawley of Cornell University.

The long-accepted dogma in the fight against obesity holds that weight gain or loss depends on calories. A calorie is a calorie, according to the U.S. Dept. of Health and Human Services, although recent research has challenged that assumption. A contradictory theory links obesity to fatty foods.

According to the Cell Metabolism study, the body treats calories differently depending on the time of day they’re consumed. That can explain why obesity treatments have been so notoriously unsuccessful, Panda said.

“For a long time, we’ve had only two recommendations for prevention. One is reduce calorie intake; the second is exercise,” Panda said.

Both these approaches have major flaws, Panda said. Restricting and measuring calorie intake is difficult, and exercise is likewise more difficult as work becomes more mechanized.

Panda, who researches circadian rhythms —- or the “body’s biological clock” —- said he decided to investigate whether that pattern had any effect on weight gain.

The reason time of eating matters is that different genes are turned on and off at different times of the day, and these influence metabolism, Panda said. During times of sleep (day for mice and night for humans), when metabolism slows down, the body lives off its stored fat.

But humans have disrupted this ancient cycle in modern times with artificial light, extending their activity, and eating, far beyond what was customary. So when we eat at night, we add food when we’re supposed to be using our own stored fat.

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