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: Eighty 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, 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, the 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 10 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 adviser 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 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.”
Berardi says that experimenting with food deprivation, under professional supervision, is “a great way to practice managing hunger.” One must learn the sensation of "true hunger" and distinguish it from the "sure, I could eat" whims that many of us call hunger.
“The better you can manage hunger,” Berardi writes, “the less likely you are to react compulsively to it. To get fit—and stay fit—you need that skill.” He advocates acceptance. “Relax. So you missed a meal. Who cares? Might even be good for you. Just keep going.”
Berardi writes that intermittent fasting is not itself better for weight loss than traditional calorie restriction; but, like Varady, he found the regimen is easier to maintain.
These studies and testimonials suggest that the every-other-day diet is a workable strategy for weight loss. But is it actually beneficial for your body? The first thing I worried about with this diet was the license it seems to give to eating the least-healthy foods.
“Are people eating terrible things?” I asked. “Like, I might be inclined to eat frosting all day. Just a couple jars of frosting after dinner, you know? Also when I’m really hungry—or, what I think is hungry—I crave calorie-dense fats and carbs. But when I eat before I get to that ‘really hungry’ point, I’m a lot more likely to get a salad.”
“We’ve studied people who are on the every-other-day diet and eating high-fat compared to low-fat—45 percent fat and 25 percent fat—and the people who ate high-fat actually ended up losing more weight.”
Varady says that may be because of adherence. People who ate the high-fat diets were more satisfied. They felt less deprived of foods they craved, and were probably less inclined to diet-cheat on the fast days. Varady also compared cardiovascular risk factors in both groups. She found that LDL, triglycerides, insulin, and blood pressure decreased similarly, regardless of how much fat people were eating.
“You know, if you look at the most recent data from the Physicians’ Health Study at Harvard, they didn’t find any links at all between fat intake and heart disease or diabetes. If you look at the NIH’s Womens’ Health Initiative study, they’re saying there’s no link between diet and heart disease risk. We might have it wrong. I’m not sure a high-fat diet does lead to heart disease. I think a cluster of factors does—stress, smoking, a sedentary lifestyle, but not a high-fat diet in itself.”
Varady earned her doctorate in lipid metabolism, and she remembers that during grad school, “We were always asking, what’s the mechanism between high cholesterol or high saturated fat and heart disease? We could never come up with it,” she said. “I’ve always thought it was strange that I graduated with a Ph.D. in lipid metabolism and couldn’t answer that pretty crucial question.”
Speaking of sedentary lifestyle, are people less likely to exercise on this diet? “Do they feel tired and lethargic on the fasting days?” I asked. “And stuffed like a lazy turkey on the feast days?”
“Wow, you’re touching on pretty much every study I’ve done, in order.”
“Oh, well that’s serendipitous. I promise I haven't been weirdly tracking your career.”
“So,” she continued, “After the fasting study, we looked at whether people can exercise on this diet? What are their activity levels?”
Varady had several experimental groups wear accelerometers, and she found that average daily activity levels were no different for people on the diet, compared to an every-day diet or no restriction at all.
As far as exercising, people didn’t do as much during the first 10 days of the every-other-day diet, but after that they did just as much. Subjects said they could exercise on fasting days without feeling weak or tired.
“But the really interesting thing about that study,” Varady said, “is that it was best to exercise in the morning on the fasting days. People tend to get a hunger surge about an hour after exercise, and they did best when the fast-day meal”—which, on Varady’s diet, is recommended to be taken at lunchtime”—came shortly after the workout.”
The people who opted to exercise in the afternoon lost less weight, which Varady says is because they got that post-workout hunger surge at a time they couldn’t eat, so they were more likely to cheat on the diet.
Not everyone is joining the intermittent fasting fanclub.
Susan Roberts, a professor of nutrition at Tufts University, told the Los Angeles Times earlier this month, "I don't think many people can do it. I can tell you that it is not easy. You get lethargic, hungry, really inward-looking because your body absolutely knows it is in emergency conditions."
"As a routine two-day-a-week thing,” she continued, “I think it would ruin your life."
The two-day-a-week thing to which she refers is the 5:2 diet, promoted by physician/journalist Michael Mosley. He took viewers on a journey of self-experimentation in the 2012 BBC2 Horizon documentary Eat, Fast, and Live Longer, which concluded with his decision to stick to two days of fasting per week, and five of conscientious eating. Mosley turned that story into a book, 2013's The Fast Diet, which became a #1 New York Times bestseller.
On the surface, The Fast Diet follows the disquieting bestseller formula—the book jacket promises a simple secret to longer life ("Lose weight, stay healthy, and live longer with the simple secret of intermittent fasting")—but his story is more nuanced and feels well meaning. It’s, refreshingly, about his own journey, not a set of scare-fueled directives for mine. Unlike Roberts, of course, Mosley does not think intermittent fasting will ruin your life.
"I love life,” he says in the opening lines of the documentary, “So I want to remain young, energetic—enjoy it for as long as I can.”
His positivity is a recurring theme in the culture of intermittent fasters. It’s not a penance of last resort. People tend to do it because they enjoy it. It’s about consciousness and the sense that you’re healthy and have a steady relationship with food and weight that fades from concern. Once people find the right balance, they commonly say the periods of deprivation are as enjoyable as the periods of gluttony.
"What I discovered was truly surprising,” Mosley says. “It involves no pills, no injections, and no hidden costs. It's all about what you eat—or what you don't eat. It's about fasting."
As the title of the BBC documentary implies, Mosley gets well beyond the weight loss aspect of fasting, into the research on longevity, cancer, and neurologic disease. Back in the 1930s, researchers at Cornell found that animals on severely calorie-restricted diets live longer than those on regular diets. Mosley makes a case that people do, too. He talks with Dr. Luigi Fontana of Washington University in St. Louis, who says, "It's astonishing how simple dietary intervention can change how the human body works." To Fontana’s eye, people who practice fasting and calorie restriction “look like a different species.” (In a good way, I infer—a species that closely approximates Homo sapiens, but looks healthier.) “They are going to live longer than their parents or brothers [who are] on the typical Western diets."
Valter Longo, a professor of gerontology at the University of Southern California, has also linked fasting to longevity. He says fasting can be a healthful option because it lessens exposure to a hormone called insulin-like growth factor 1 (IGF-1). His research shows that IGF-1 is tied to many chronic diseases like diabetes and cancer, and that eating exposes your cells to more IGF-1. People born with less IGF-1 have been shown to live longer and healthier.
Fontana has found the same. As he and colleagues wrote in the academic journal Aging Cell, "Our data provide evidence that protein intake is a key determinant of circulating IGF-1 levels in humans, and suggest that reduced protein intake may become an important component of anticancer and anti-aging dietary interventions." Fontana calls high IGF-1 a major risk factor for cancer.
Mosley also talks with Dr. Mark Mattson, a senior investigator in neuroscience at the National Institutes of Health, who has shown that short bouts of fasting can have cognitive benefits, and that alternate-day fasting can delay Alzheimer's disease in mice.
Varady says the 5:2 diet is unsubstantiated. “Unfortunately people take my alternate-day fasting studies and apply them to fasting only one or two days per week. That hasn’t actually been proven to work. We don’t know what happens. It’s a little frustrating. I know you don’t get the same hunger-suppressing effect, so people tend to binge on their feast days.” (Mosley has actually since moved to a maintenance regimen of one day of fasting per week. His weight has stayed stable.)
“I get a lot of obese people contacting me,” Varady says, “telling me they tried the 5:2 plan and ended up binging on the feast days and actually gaining weight.”
I asked Varady about longer fasts, and the sorts of popular diets like “cleanses” that are essentially fasts, where you might only be drinking lime juice with pimentos and vinegar for 10 weeks.
“There are so many of those diets, and everyone asks me about that,” she says. “I’d never really looked at popular diet books in the bookstore until now, and it’s just like, wow, most of these have zero scientific evidence behind them. Even the Atkins diet, they really only started researching it after a million people were on it.”
Varady says that if people are on a cleanse where they’re basically only drinking sugar water, and getting no protein, they are probably going to lose a lot of lean (muscle) mass. The problem there is that as lean mass decreases, metabolic rate decreases.
“Then when they’re done with the cleanse,” she says, “even if they eat barely more than they did before, they will gain weight at a pretty fast rate.”
So it’s clear that there’s a lot more to be learned here. But these ideas are exciting. Hopefully more research continues to show this is a beneficial way of eating, because it’s not only easy to learn and accessible, and apparently, for many, enjoyable—it’s also cheap. One great thing about eating less food is you buy less food.
Finally, the thing that really endears me to this diet is the forthrightness of its champions. Varady, Mosley, and Berardi are all extremely—almost eerily, by diet-advocate standards—upfront that this way of eating is promising but in its early stages of research. They also all say that it’s not for everyone. They don’t sell it like a magic bullet, but like an exciting thing for healthy adults to try out, with the blessing of their doctor.
As Berardi, who runs a clinic and sells his own book about the diet, put it, “It’s a helpful tool and one I’ll continue to use periodically. But it’s not the end-all, be-all of nutrition or fitness. People have been getting in awesome shape—and staying in awesome shape—for decades without the use of intermittent fasting.”
“I’m not saying this is for everyone,” Varady told me. “For some people it works. I run a Facebook page with, like, 2,500 people on it. Some of them just love it. Some have been on it for years. I’m just putting it out there as a viable option.”
Ultimately, Berardi says, the benefit of this diet is in calling attention to the few commonalities among successful diets: controlling calories, learning the basics of good nutrition, and eating quality food. Also, exercising. “Those things,” he writes, “are enough for most people to get in the best shape of their lives.”
If not the best shape of our lives, at least hungry.