Let's get this out of the way: No one's recommending you sit down and eat for eight hours. But a Salk Institute study published in the journal Cell Metabolism, shows that if you condense the total time you eat each day to only eight hours -- say 8:00 a.m. to 4:00 p.m. -- you can prevent weight gain and reduce diabetes risk, without changing your total calorie consumption.
Again: if you eat exactly the calories you're currently eating, but squish the total time you eat into eight hours a day, you'll avoid packing on pounds and lower your risk of all sorts of metabolic badness including diabetes.
"Of course, the foods you eat matter," says Satchin Panda, Salk Institute researcher and the paper's senior author, "But we showed that when you eat is just as important as what."
The seeming magic of fitness without eating less hinges on the function of mitochondria in your liver. Among other things, these mitochondria process food, cycling through a defined schedule of work and rest. While they rest, mitochondria divide. And if you eat while they're dividing, you force them back to work -- disrupting their metabolic cycle and leading to a higher rate of DNA damage than in mitochondria that aren't bombarded by burritos when they're trying to get their division on.
At Salk, 8-hour feeding mice used nutrients more efficiently and had more energy than free-feeding mice. Astoundingly, the study writes that these 8-hour mice, were also "protected against obesity, hyperinsulinemia, hepatic steatosis, and inflammation and have improved motor coordination."
Despite the header of its Wikipedia entry encouraging readers not to confuse it with foie gras, hepatic steatosis or "fatty liver" is no joke.
"Our circadian clock separates functions throughout the day so that our organs stay healthy," says Panda. But the clock in your liver isn't a sundial -- it doesn't simply monitor lightness and darkness and click through its organ functions based on time of day. Instead, "it gets information about time by when we eat," says Panda. Your liver needs to know when you've taken your last bite of the evening so that it can tell mitochondria it's safe to divide. "And if you eat all the time, the clock gets the clue too many times, it tries to adjust too many times, and it never knows when it's breakfast," says Panda.
This forced adjustment of circadian rhythm and the resulting mitochondria damage is one reason that shift workers -- who are nocturnal on weekdays and then try to adjust to a diurnal schedule on weekends -- have 150 percent higher rates of metabolic disease than workers with standardized schedules of eating and sleeping.
And, Panda points out, with people in the United States now averaging more than 160 hours of TV viewing per month, "we have 100 to 120 million people who are social shift workers," he says. Led by the TV's silver tongue, Americans have made the social decision to act like shift workers. "And this population is more at risk for every type of metabolic disease," says Panda.
So don't be a social shift worker. Your mitochondria will thank you for it. And if you want to lose weight on your current high-fat diet, eat your calories in an eight-hour window.