I am so hungry. Not quite ravenous, but definitely a few notches north of snacky. I’m hearing the opening salvos of stomach rumbles. It’s made drifting off to sleep more challenging than usual, so I get up and chug a big glass of water, hoping it will take the edge off. In the kitchen, I can still smell the leftover beef ragù my wife had over fresh pappardelle, callously topped off with shaved pecorino. During “dinner,” I found myself glaring at her through the thin steam coming off my green tea.
To fall asleep, I soothe myself by thinking about the huge amount of food I’ll devour tomorrow and how the simple diet I’m test driving—I eat very little one day and whatever I want the next—is promised by science to reveal the abs I supposedly have. But looking good at the beach isn’t the half of it. According to a growing pile of research, alternate-day fasting, or ADF, will prevent a long list of diseases, including cancers, Parkinson’s, Alzheimer’s and diabetes; and slow the aging process to a crawl, adding years to adherents’ lives. Best of all, chowing down on a rack of ribs and a wedge of cheesecake, then washing it all down with a few frosty beers, is tacitly approved. In fact, research shows it’s the diet that every homo sapiens was made for.
We live in a time in which food is plentiful for most people. Today, fewer than 1 in 3 Americans older than 20 are neither overweight nor obese. This overabundance of food energy is a new thing in the scope of human evolution. See, our hunting-and-gathering forebears had little control over when they got to fill their bellies. Back then, a feast of flame-broiled kudu meat on Monday might be followed by half a wizened tuber and a schmear of wild honey on Tuesday, then nothing at all on Wednesday or Thursday.
“There are two things our pre-agrarian ancestors did better than anything else: Fast and have babies,” says Marc Hellerstein, Ph.D., a professor of metabolic nutrition at the University of California-Berkeley. Humans who could cope with an inconsistent food supply survived long enough to procreate, then passed the ability to their children. Thousands of generations later, here we are: Hard-wired to feast and fast, but most likely eating three meals a day and snacking in between. It’s a calorically consistent lifestyle that we’re not yet adapted to.
Alternate-day fasting seems to be the way to have your cake, eat it, then go back for more cake—with a bit of advance planning.
If we decide to deal with the apparent misuse of our system, it’s usually not until we’ve packed on a pound too many. Then, we typically create a daily calorie deficit: Eating less than we expend through exercise and other bodily processes that require fuel. It’s commonly known as a diet. When executed correctly over a long period of time, that strategy works. But daily caloric restriction (CR) is not much fun, frankly, and is ultimately unsustainable for most people. ADF, on the other hand, seems to be the way to have your cake, eat it, then go back for more cake—albeit with a bit of advance planning.
“Studies have shown that while people will lose weight with daily CR, they don’t stick to it for very long,” says Krista Varady, Ph.D., an associate professor of kinesiology and nutrition at the University of Illinois at Chicago. “Daily CR means always watching what you eat and usually feeling hungry a lot of the time. But with ADF, you’ll feel hungry one day, but there’s always the next day to look forward to—a day when you can eat ad libitum, meaning as much as you like.”
As one of the world’s most prolific researchers on alternate-day fasting, Varady has written a number of papers on the regimen’s various outcomes. To ensure that overweight study participants don’t mutiny during their fast days, Varady allows them one small meal (about 500 calories) between 12pm and 2pm. This is about 25% of their normal total energy expenditure, or TEE.
“As participants eat a small meal, technically this is alternate-day modified fasting,” she says, adding that a small meal helps with adherence to the diet. The short midday timeframe ensures that subjects are in a fasted state for most of the day.
Every other day, I get to eat whatever I want, and this will give me a trimmer waist and add years to my life? Doctors say yes.
To try out ADF for myself, Varady suggests that I first determine my TEE via the same method used in her lab. I plug my vitals into a formula to figure out my resting metabolic rate, or RMR. For men, this equation is (10 x weight in kg) + (6.25 x height in cm) – (5 x age) + 5. My RMR, or the food energy my body and brain need just to idle, is 1,534 calories.
Then I calculate my average TEE by multiplying that result by a value representing my activity level. For a non-exerciser, this number is 1.2, while an athlete or manual laborer can multiply his RMR by 1.9. As a fairly active man who exercises moderately five times a week, I get to multiply my RMR by 1.55. My TEE—the amount of calories my body needs—is 2,377.
A quarter of that figure—594 calories—is what I can eat on my fast days during a two-hour midday window. What form that takes, Varady says, is up to me. She cites a 2012 study conducted in her lab which showed that a high-fat ADF diet was just as effective as a low-fat ADF diet in aiding weight loss.
Of course, I’m already thinking about the prospect of scarfing a pint of Ben & Jerry’s and calling it lunch. But knowing that my stomach will be roaring by bedtime, I should ensure that my fast-day meal is high in protein, which has been shown to stave off hunger more than carbohydrates and fats in several studies.
So what are guidelines for the feast day? Well, there are none. Varady and Leonie Heilbronn, Ph.D, an associate professor at the University of Adelaide, have independently conducted studies that show people only consume about 20% more than their TEE when they have the chance to go hog-wild. “It’s funny,” says Varady. “The study subjects tell me about how they make a big breakfast with eggs, bacon and pancakes for their feast day, only to find they can’t eat it all.” She suggests it might be related to the stomach contracting over the course of the fast day. Heilbronn observed similar behavior in her studies on human subjects but the opposite effect in rodents, which had no qualms about gorging when the opportunity presented itself.
So if I’m hearing this correctly, every other day I get to eat whatever I want, and this will give me a trimmer waist and add years to my life? Doctors sitting on stacks of peer-reviewed evidence say yes.
How can these two diametrically opposed strategies both decrease fat and retain muscle?
For a guy who wants to drop a little flab while retaining hard-earned muscle, findings on body composition are revelatory. In a 2011 article published in Obesity Review, Varady demonstrated that calorie-restricted dieters and alternate-day fasters lose about the same amount of total weight, fat mass and visceral fat (fat surrounding the internal organs). But daily dieters lost about a pound of muscle with every three pounds of fat, whereas ADFers would have to lose nine pounds of blubber to sacrifice a pound of brawn. “If you’re looking to lose fat and conserve muscle,” she says, “trying some form of ADF might be a good strategy.”
At this point, I should mention that fasting for any length of time goes against received wisdom re: improving body composition. The commonly held belief is that metabolic rate should be increased to reduce body fat and is achieved by increasing exercise and eating several small, protein-rich meals throughout the day. Fasting, on the other hand, causes the metabolism to slow. So how can these two diametrically opposed strategies both decrease fat and retain muscle?
“I think the numerous meals [idea] is a heresy,” says Eric Ravussin, Ph.D, director of the Nutritional Obesity Research Center at Pennington Biomedical Research Center in Baton Rouge, Louisiana. If you’re always eating, says Ravussin, your body is always producing insulin, the hormone central to regulating carbohydrate and fat metabolism in the body. Fat is fuel that’s in storage, and if you’re mainlining grub all the time, your body doesn’t get to tap into the stockpile.
Ravussin and others believe it’s ideal is to maintain a slower metabolic rate while resisting the weight gain that can accompany it. Why? If you slow the rate that chemical reactions are taking place in the body, you’re effectively checking the speed at which cells divide. That’s not only a hedge against cancer; it can put the brakes on the aging process itself.
“The body is an incredibly efficient piece of equipment,” says Hellerstein. “Over millions of years, it’s been honed to expend less energy when the fuel supply drops off.” He explains that the body quickly downshifts into a lower gear when in a fasting state and that cells, including cancer cells, will multiply at a greatly reduced rate.
Scientists have long known that animals on a daily CR diet significantly outlive their free-eating counterparts—but new studies are showing that alternate-day fasting yields similar results. To reap the benefits of a slower metabolic rate without piling on the pounds, an ideal strategy might be to combine fasting and exercise. A recent study by Varady concluded that ADF, in conjunction with endurance exercise, produces superior changes in body weight, body composition, and heart-disease risk than ADF or exercise alone. Another recent study from Belgium showed that training in a fasted state improved glucose resistance and insulin sensitivity.
When blood isn’t being diverted to help with digestion, there’s more of it for the heart, lungs and muscles—and your performance in the gym.
But can you truly “bring it” when your fuel gauge is in the red? It depends. “VO2-type training has been proven to improve with fasting due to the greater reliance on fats as a fuel source,” says Robb Wolf, a former research biochemist and one of the world’s leading experts in Paleolithic nutrition. “Strength training may not be optimal fasted as it requires a heavy neurological component.” But Wolf adds that when blood isn’t being diverted to help with digestion, there’s more of it for the heart, lungs and muscles to aid with your performance in the gym.
Deciding when to start the program required looking at my social calendar for the next month and trying to ensure that the fast days don’t fall on most of the social events I have planned. During the 30-day experiment, my fast-day mornings are fine; I suspect I’m often somewhat full from the previous day’s food orgy. I brew a big pot of strong coffee, and when I do start to get really hungry, I put on my sneakers and do a 50-minute run.
Both resistance training and aerobic exercise have been shown to curb hunger pangs during the workout and for a short time afterward. But 45 minutes after my run, the hunger is back with a vengeance. After a while, push-ups no longer keep it at bay. I usually hold out until around 1:30 or 2pm, then make a stir-fry of 3 cups of chopped cabbage, 1.5 cups of sliced mushrooms, some sliced turkey with a quarter-tablespoon of sesame oil, then top it off with two poached eggs. That’s about 400 calories. The remainder of my allowance is taken up with protein powder, which I mix with water instead of milk. In this meal, there’s the hunger-reducing protein and a plenty of fiber. Lots more water and green tea hold me over until dinner, when my wife comes home to make something annoyingly delicious for herself. “I’m not sure I like you on this diet,” said my wife when I got terse with her one evening. “You’re sort of a nightmare.”
Though I don’t admit it, I know she’s right. When I tell Eric Ravussin about my mood changes, he knows exactly what I’m talking about. “When I did three weeks of ADF, my wife said ‘never do that again,'” he reports.
Even though my mental state might suffer during periods of fasting, studies have shown that over the long term, ADF can protect the brain against age-related diseases like Alzheimer’s. Mark Mattson, Ph.D, a senior investigator at the National Institute on Aging, explains that during the diet I’m on, the cells of the brain are put under mild stress that is similar to the effects of exercise on muscle cells. Why does this happen? Mattson points to our origins in Africa. When resources became scarce, our ancestors would have had to scrounge for food. “Those whose brains responded best, who remembered where promising sources could be found or recalled how to avoid predators, would have been the ones who got the food, and a mechanism linking periods of starvation to neural growth would have evolved,” he says.
I’ve consumed 1,500 calories in one sitting. By the end of my gastronomic rampage, I’m in the 4,000-calorie range.
After the first week to ten days, I fell into a rhythm, and my moodiness was offset by a general sense of emotional and physical well-being. On feast days, I woke up feeling like a kid at Christmas. The feelings of acute hunger had passed and were replaced by a feeling of emptiness. After a cup of coffee, however, the pangs came back with a vengeance, but I self-medicated with pancakes topped with butter, maple syrup and caramelized bananas, then a second breakfast of Greek yogurt and honey. “I thought it was eat as much as you like, not as much as you can,” quipped my wife. When I totaled the damage, I realized I’d consumed 1,500 calories in one sitting. Lunch and dinner were a similar story. By the end of my gastronomic rampage, I was in the 4,000-calorie range.
Though Varady recommended that I put no restrictions on my eating, she was unaware of my propensity to pig out. Just to make sure I wasn’t taking her instructions too far, I re-combed through the scientific literature and found a paragraph stating that male study participants who considered themselves “big eaters” didn’t lose as much weight as those who used some restraint on their feast day or, as my wife called it, “common sense.” I took my gluttony down a few notches.
Admittedly, on some fast days, consuming less than 594 calories is just not going to happen. (I defy anybody to attend a baseball game on a warm April day and say no to a fully loaded bratwurst and an ice-cold beer.) But aside from a few slip-ups, I kept to the schedule. I’d read that fasting improves the way food tastes after a while. It could be psychosomatic, but I definitely seemed to appreciate the way food tasted more that I previously had.
Many fasting enthusiasts say that fasting sharpens the senses, especially taste.
After my four-week trial, my doctor confirmed that I’ve had to cut a new notch on my belt. “You’ve lost seven pounds, you’ve reduced your BMI by over a percentage point and your blood pressure has improved,” he said. Blood tests revealed that my glucose and triglyceride levels had dropped, and my ratio of “good” HDL cholesterol to “bad” LDL cholesterol had improved dramatically.
When I plugged the new values into a handy heart-health app, I found that I’d dropped my cardiovascular age from 32 to 30 and decreased the likelihood of cardiovascular disease over the next 10 years. (All this change in just four weeks.) Upon reviewing my results, Varady commented that the changes were typical of the improvement she sees with her study participants, despite the fact that I had a BMI in the healthy range to begin with.
The big promises of alternate-day fasting over a much longer time period include a lower incidence of potentially fatal diseases, a general slowing of the aging process, prevention of many neurodegenerative disorders and an incredible 30% jump in lifespan. But could I maintain a feast-and-famine lifestyle forever?
I think I could. After my four-week trial of ADF came to a close, I went back to eating the same amount I used to. I soon noticed that I didn’t feel quite as good and that I wasn’t enjoying my meals as much. Many fasting enthusiasts say that fasting sharpens the senses, especially taste. So after about a week, I jumped back on the ADF wagon, because I preferred it as a lifestyle. This, despite hardly ever having skipped a meal in my life prior to this challenge. Going slightly hungry one day and eating and drinking whatever I like the next is a great fit for me. The myriad health benefits are just a bonus.