Could we avoid obesity and diabetes just by restricting the number of hours a day we allow ourselves to eat?
Mice whose hours of eating are restricted stay healthy and maintain a normal weight, even when they eat a high fat diet.
Many of our organs have clocks that determine when they work most efficiently.
Restricting eating hours takes just as much willpower as dieting.
By cramming all of your eating into a smaller number of hours, you might be able to reduce your risk of obesity and related diseases, suggests a new mouse study -- even if you continue to eat exactly the same amount of food that you were eating before.
When given the same quantity of high-fat food, mice in the study that ate throughout the day and night became fat and sick, while mice whose eating was restricted to a period of eight hours remained healthy.
Researchers suspect that a period of fasting may boost the efficiency of organs involved in metabolism, allowing the body to better regulate blood sugar, fat storage and other measures. Each organ might also have its own clock that is programmed to work best during the hours when eating fits in to our circadian rhythms. Eating outside those rhythms, on the other hand, could set the body up for trouble.
"If you look at the nighttime view of the sky in NASA satellite pictures and then go back to the Gallup survey on diabetes and obesity, these two pictures overlap nicely, which means that the places that are lit up late into the night have higher incidences of diabetes and obesity," said Satchin Panda, a molecular biologist at the Salk Institute in San Diego.
"People are still stuck on calories in and calories out," he added. "What we are saying is that the body uses calories in during the day very differently from calories in at night."
For millions of years, Panda said, humans ate most of their food in the daytime. With the invention of electricity and then shift work, followed by 24-hour TV channels and an emphasis on nighttime socialization, recent decades have seen a shift in the way we tend to eat.
Instead of confining meals to a 12-hour stretch, many people regularly graze over a period of 16 hours or more. And coincidentally, rates of diabetes and obesity went up and up.
Prevailing theories explain the obesity epidemic by suggesting that, through overeating and inactivity, people consume too many calories and that they burn too few. Panda wondered if the timing of food intake might matter, too.
After all, studies in recent years have revealed that the brain is not the only organ with a circadian clock. Skin, eyes, stomachs, livers and other organs also have clocks that determine when they work most efficiently, just like the brain's clock regulates sleep cycles.
To see whether eating over a longer period of time each day might be contributing to obesity, Panda and colleagues fed high-fat diets to two groups of mice with identical genes. The only difference between the groups was that for one, food intake was restricted to eight hours. The other group was allowed to eat at all times of day and night -- and they did.
For more than four months, both groups ate equivalent amounts of food. But by about a month into the study, the mice that were eating all the time had started to become obese, the researchers report today in the journal Cell Metabolism. By six weeks, mice that ate around the clock had developed high blood sugar. By nine weeks, they had full-blown diabetes. Their cholesterol levels were twice as high as normal. And their livers showed extensive damage.
Mice who ate for just eight hours a day, on the other hand, remained healthy. They were also able to run for the longest time in an exercise test, showing that the fasting period had not detrimentally stressed them out in any way.
One explanation for the results is that circadian clocks throughout the body set an ideal eating period when metabolism happens most efficiently. Another possibility is that it's simply a period of fasting that's necessary to reset genes involved in efficient metabolism. If that's the case, and the same applies to people, the research could suggest a simple way to control your weight: Confine your eating to a certain number of hours per day.
But that may be easier said than done, said David Mangelsdorf, a biochemist at the University of Texas Southwestern Medical Center at Dallas.
"We have known for some time now that the pathways governing metabolism are synched to the time of day that organisms normally eat and store nutrients appropriately," Mangelsdorf said. "Regarding the use of this schema as a means to control obesity, it may very well translate to humans."
But restricting hours of consumption would require just as much willpower and commitment to making lifestyle changes as dieting does, he added. "It works in mice because they are forced to eat at only a certain time of day."