Before she deprived people of food, Dr. Krista Varady deprived mice. Not for long, and not entirely, but during her post-doc research at the University of California Berkeley in 2006, Varady helped them learn what real hunger was. She wanted to know how short-term fasting affected their appetites and weights. She would let them eat only a quarter of their normal diet on one day, then give them access to as much food as they wanted the next.
Varady called the days of austerity “fasting” days–even though, generally, a fast is complete deprivation of food. She called the days of gluttony “feasting” days–even though, to my mind, no quantity of rodent feed-pellets constitutes a feast.
The days rolled by sequentially for the mice: fast, feast, fast, feast, fast, feast. Varady tracked how much they ate on the feast days, and how much their weight changed. What she found surprised her. (Like many scientists, Varady’s descriptor of choice for her research findings is “surprising.”) Even on the days that the mice had access to unlimited food, they only ate about 25 percent more than average. They did not eat enough to compensate for the fasting days. So, over time, they lost weight.
Does that work in people?
"To be honest," Varady told me, "at first it seemed a little crazy to me." That fraction of an average (2,000 calorie) diet for people is 500. "Can you really ask someone who's 250 pounds to only eat 500 calories?"
It turns out you can. After Varady first published the mouse studies, a handful of people contacted her saying they had been on the same sort of diet for years. Loved it. She developed a protocol for humans based on her mouse experiments, and enrolled her first study subjects in 2008. She was surprised to find that, like mice, when people are given only 25 percent of their caloric needs on a fasting day, they do not eat 175 percent the following day. They actually only eat slightly more—115 percent or so. That means by the end of the week, they’ve eaten a lot less than they typically would, and they only felt deprived for 3.5 days. Another surprise: 80 to 90 percent of people were able to stick to the plan.
Today Varady is an associate professor of kinesiology and nutrition at the University of Illinois at Chicago and the author of a glossy diet book, The Every-Other-Day Diet, which came out, like so many of its kind, at the turn of the new year. The every-other-day diet is a relatively mild variation on the established practice of “intermittent fasting”–a diet strategy that has had a small but ardent following for years. At extreme ends, intermittent fasting can involve total deprivation, for longer periods. Varady’s version is intended to be approachable enough for the casual dieter; easy to learn and remember and sustain long-term. Potentially forever.
The most common weight-loss diet people attempt is calorie restriction. Eat less, or just fewer calorie-rich (delicious, dopamine-generating) foods. The problem is that we tend to quit because we feel deprived. Life without life’s joys is living death. It’s okay to sometimes be the one who doesn’t have any birthday cake. But always? Am I always going to be that person who refuses cake? Or the one who occasionally refuses, and occasionally feels delinquent for not refusing?
On its face, every-other-day diet is a compelling alternative. What if we can be ruthlessly judicious about our diets half of the time, and half of the time eat without reservation or guilt, and actually end up healthier than a full-time dieter?
Varady’s research suggests that this on-and-off pattern might be more successful than traditional techniques. She is currently conducting an NIH-funded research trial in which people are doing six months of every-other-day dieting as compared to six months of every-day calorie restriction. At the end of a typical week, both groups eat about the same number of calories. "We're actually seeing," though, she said, "that the people in the every-other-day group are losing more weight—about five to seven pounds more—because they're just able to stick to it longer."
"And they like it more. They like that they're always able to look forward to the next day when they can eat whatever they want. They are able to feel normal sometimes."
“So, do people do this for their entire life?” I asked. “Will they eventually lose all of the weight and weigh nothing?”
“As an obesity researcher, I’ve seen that obviously you can’t just go on a diet for a while and lose weight, then go back to what you were doing. You’re going to gain that weight back. You need to find something you can adhere to.” That’s where her “maintenance regimen” comes in. The NIH study will transition to a point where instead of eating 500 calories on the fasting day, people eat 1,000. Her early data says that works for keeping weight steady.
The results seem clear, but their cause is not. "The reason they lose weight is that something keeps people from really binging on that feed day,” Varady says. “Something changes in the body on the fasting days. We're not sure what. It may be hormone changes, or that the stomach shrinks."
Measuring the size of a stomach is invasive—it involves putting a balloon in a person's stomach while they are undergoing an MRI—but she says that's something she will eventually do.
She says the first ten days are "pretty difficult," but after that, people seem to get used to it.
There's also an idea, proposed by many fasting adherents, that the practice helps us become familiar and comfortable with the sensation of hunger. One voice for that idea is John Berardi, an Ontario-based nutritionist with a PhD in exercise physiology and nutrient biochemistry. He has been an advisor to Apple, Equinox, and Nike; and Livestrong.com named him among “20 of the Smartest Fitness Trainers You Might Not Know.”
Berardi is also a self-described “professional dieter”—which is to say, he doesn’t just talk smart, he talks from experience. He claims to have personally tried “nearly every diet or nutritional protocol that’s around, to test its efficacy.”
“As a competitive, masters-level track athlete and life-long fitness enthusiast”— in 1995 Berardi won a national junior bodybuilding title—“I wanted to test a new way to drop fat and get extremely lean, while staying strong and powerful,” Berardi wrote in his eminently readable e-book, Experiments With Intermittent Fasting. Berardi details in over 80 pages his experiences with six different fasting protocols over the course of six months.
"I kept meticulous notes on everything," he writes, "from scale weight, body-fat percentage, and blood/hormonal markers, to lifestyle markers like energy levels, cognitive thought, and pain-in-the-ass factors."
He came away with the idea that even a few days spent messing around with this type of dieting can be beneficial long-term. Berardi himself ended up losing 20 pounds, decreasing his body fat from 10 to 4 percent (he was doing very well already, and by the end he was a spectacle of leanness). He came out of that trial period with “intermittent fasting strategies that [he] could follow indefinitely with no problem,” he writes, “in a way that was easier and less time-consuming than ‘traditional’ dieting.”