Meal times determine weight gain in mice

Mice that could only eat for eight out of every 24 hours stayed healthy, while those allowed to snack all day long on the same foods gained weight and lost motor skills, a new study reports.
Mice that snacked at will exhibited 28 per cent weight gain, on average, whereas mice that were only allowed to eat during an eight-hour daily period did not become obese. (Yoshikazu Tsuno/AFP)

Mice that were only permitted to eat during an eight-hour span each 24 hours stayed healthy, while those allowed to snack freely all day long — and who consumed the same number of calories — gained weight and lost motor co-ordination, according to a new study.

The results suggest that it is as important to consider when one eats as well as what one eats, at least for mice.

California researchers divided the critters into four sets: two groups were fed healthy diets and two consumed high-fat foods.

As well, one each of the healthy and high-fat groups were only allowed to eat during an eight-hour period each 24 hours, while the others could munch away as often as they wished.

The high-fat groups were given the same number of calories, but the health of the mice with no time limits on their eating deteriorated considerably over three months compared to those with the restricted mealtime.

The average weight of the free-eaters jumped 28 per cent in that period. They also developed liver problems, intolerance to glucose and inflammation of bodily tissues.

The restricted-mealtime mice, by contrast, didn't become obese and showed improved motor co-ordination.

Circadian rhythm involved

These results can be made sense of in several ways, the California researchers say.

One explanation is that the time-restricted feeding period gives the body's metabolic system a chance to do its work without being constantly bombarded by new food intake.

Another important consideration is that a time-restricted diet reinforces the mice's innate metabolic clock, known as the circadian rhythm, by clearly distinguishing active waking hours from resting times.

Stronger circadian rhythms, in turn, tend to improve the performance of molecules that play an important role in food intake, including a protein called mTOR that regulates cellular nutrient levels and genetic processes, and an enzyme called AMPK that hinders the formation of cholesterol among other duties.

That line of thinking echoes results from German research published last week that found that humans whose sleep hours are too early or too late for their body clock tend to gain weight.

The authors of the mice study say their results show that there are ways other than medications to fight obesity and its associated illnesses.

The researchers are from the Salk Institute for Biological Studies and the University of California. Their paper was published online Thursday in the journal Cell Metabolism.