The 8-Hour Diet

Americans are trapped in a 24-hour eating culture, and our bodies are paying the price. Can we trim our waistlines by cutting back our time at the table?

December 17, 2012

Standing in a dark conference room at the Salk Institute for Biological Studies in La Jolla, California, Satchidananda Panda, Ph.D., is at the epicenter of a research movement that has rocked conventional weight-loss thinking to its core. Gesturing toward a big-screen display, Panda clicks over to a pair of maps. The one on the left shows the varying degrees of darkness and light pollution in the night sky over the continental United States. The one on the right: diabetes incidence, county by county, in the U.S. population. The charts have been adjusted to control for the greater population numbers in city areas, but still, the two are mirror images of each other.

"Where there are more lights," he says, "there is more diabetes." Those aren't refrigerator lights depicted on the night map, but they might as well be, given the effect on all of us.


Panda goes on to explain what may be happening: "My hypothesis is that staying up and eating late may be the cause. [Early on] we didn't know how to use fire. In the daytime, human beings would hunt something, eat something; but in the nighttime they had to protect themselves against predators. It was only about 200,000 years ago that we learned how to control fire, and only a few people could use fire to stay up past sunset. For the past 50 years or so we've been staying awake late into the night. That's when we see the rise of weight problems."

He has a theory about the mechanism behind it: The advent of artificial light has also led to an artificial extension of our feeding times. Our circadian rhythms have a natural stop sign built into them, and we run into that sign almost every day. Think about how you regularly sidle up to a bowl of ice cream while watching Leno, or stop at Wendy's for a late-night drive-thru snack. Modern technology has created an artificial daytime for us, and we're filling it up with meal four, meal five, and meal six. That extended eating interval throws our digestive system off-kilter and messes with the many hormones and enzymes that manage it. Our bodies can't process the food we eat, and those calories end up where they shouldn't—around our bellies and butts.

Not convinced yet? Hang in there.

Panda's laboratory devised an ingenious study to test his ideas on mice. The mice were divided into two groups and put on the same high-calorie, high-fat diet: One group was given the freedom to eat anything at any time of day. The other mice could eat as much as they wanted but only within an 8-hour time frame. The study went on for 100 days. Guess which group was plumped up?

"Simply limiting food intake to 8 hours gives you all the benefits—without having to worry about food intake," Panda explains.

For years we've been told, "You are what you eat." Turns out, we are when we eat too. (Pick up The 8-Hour Diet to learn how you can lose 20 pounds or more with this revolutionary approach.)


What Panda and his voluptuous vermin are discovering isn't entirely new. For several years, researchers have also seen remarkable weight-loss results in people using a technique known as "intermittent fasting."

Don't let that f-word scare you. In this case, fasting isn't about denying yourself anything. Instead it's about simply eating what you want but staying within a sensible 8-hour window.

The fact is, you're already fasting on a daily basis. Think for a moment about the word "breakfast." It is exactly the sum of its parts—the point of the day at which you break the fast you started whenever you stopped eating the night before. In the simplest terms, the 8-Hour Diet is a way of extending the period between your last snack and your "break fast," giving your body the chance to burn away your fat stores for the energy it needs.

And burn them it does. Consider this 2007 American Journal of Clinical Nutrition study: Researchers divided study participants into two groups and had each group eat the same number of calories—enough for them to maintain their weight. The only difference: One group ate all their calories in three meals spread throughout the day, while the other practiced intermittent fasting, eating the same number of calories but in a restricted time frame. Among the results: Participants who ate in a smaller window of time had a "significant modification of body composition, including reductions in fat mass." (Find out how to use the findings to shed body-fat in The 8-Hour Diet, the new book from Men's Health.)
Part of that fat burn comes simply from the body's searching for energy and finding it in your belly. But part of it is also from a surprising source: According to Panda's research, restricting the time period during which you eat makes your body burn more calories throughout the day. That's right: The longer you feed, the lazier your metabolism becomes. But fit your food intake into an 8-hour window and your body steps up to the plate, burning more calories day and night. (Check out the plan on the next page.) And new evidence shows that weight loss is just the beginning of intermittent fasting's range of health benefits.


Diabetes may well be our nastiest national plague, one that can simultaneously increase your risks of heart disease, stroke, hypertension, sexual dysfunction, blindness, amputation, and kidney disease. Yes, it's that bad. But fasting, as it turns out, can help prevent the disease from even developing.

In a study at the University of Copenhagen, researchers found that when men fasted every other day for 2 weeks, the insulin in their bodies grew more efficient at managing blood sugar.

And Benjamin Horne, Ph.D., director of cardiovascular and genetic epidemiology at the Intermountain Medical Center Heart Institute in Utah, has also studied people who stretch out the time between meals. His conclusion: "We found something we did not anticipate, which was that people who fasted also had a lower risk of diabetes. We looked at just regular diabetes, but we also looked at body mass index, baseline glucose, and glucose during fasting and found that people who have been routinely fasting over the years have a significantly lower body mass and blood sugar."

It's the physical cliff of our age, and it may be that we've now found a simple way to keep from plunging over. Take regular breaks from eating, and watch your waist and risk shrink.


Imagine eating whatever you want (within reason) and being able to slash your heart attack risk just by watching the clock. That was the promise offered up by a study published last year in the American Journal of Cardiology. The researchers found that people who followed a regular fasting plan—stretching out the period between their last meal today and their first meal tomorrow to 24 hours—enjoyed a 58 percent lower risk of coronary disease, compared with those who didn't follow this plan. This backed up the findings of a 2008 study of nearly 448 people, who demonstrated a similar ability to sidestep the cardiac ward with the same eating strategy.

Horne, whose team conducted both studies, says, "We redid the study among a different group of patients to see if we could replicate the results. We found essentially the same results—that people who fast routinely have a lower risk of coronary disease." And do you remember the fat-mouse-versus-skinny-mouse paradigm presented by the Salk Institute's Panda earlier in this story? The bloodborne markers for heart disease—inflammation, high cholesterol—were much higher in the round-the-clock rodents than they were in the 8-hour wonder mice.


There are few of us who haven't had loved ones touched by the disease. Cancer happens when the body's cells, which grow and divide constantly, begin to multiply out of control, impeding normal functions. Each moment of cell division, something that happens at least tens of thousands of times a day, is an opportunity for something to go haywire. But what if you could slow that cell growth? That's one tachometer you don't want to redline. Cancer strikes for many reasons, and a lot of them aren't fully understood. But one contributing factor to our cancer risk is our diet, including the tremendous amount of food we're regularly exposing our bodies to.

The process of cell reproduction in the body is sort of like an oven—the more fuel you toss onto it, the hotter it burns. So when we eat morning, noon, and night, we constantly feed that fire. But if we enjoy all our favorite foods in whatever quantities we want but allow the fire to dampen for an extra few or more hours during the day, then we dramatically decrease our risk of cells multiplying out of control.

"The body is an incredibly efficient machine," says Marc Hellerstein, M.D., Ph.D., a professor of nutritional science and toxicology at the University of California at Berkeley. "Over millions of years our machine has been honed to expend less energy when the fuel supply drops off." In a fasting state, cells, including cancer cells, multiply at a greatly reduced rate. "Periodic fasting can prevent cancer, we think, by slowing the rate at which all cells in the body divide," he says. "It turns the gear down—instead of liver cells, breast cells, prostate cells dividing every 3 days, they divide every 6 days. The cells don't have such a chance of heading toward carcinogenesis."

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