The Every Other Day Diet - Interview with Dr. Krista Varady

Intermittent Fasting Researcher Explains the Science

Caveman Chasing Wild Animal with Club, Painting
In caveman days, there would be a similar eating pattern: a big kill, then leaves and berries until the next big kill. Ian Watts / Getty Images

Intermittent fasting is a relatively new strategy for weight loss which takes its cues from the anti-aging science of calorie restriction. The approach was popularized in a 2012 BBC documentary called Eat, Fast and Live Longer - a program highlighting the research work of nutrition scientist Krista Varady. 

An associate professor at the University of Illinois (Chicago), Varady has condensed her numerous research papers on intermittent fasting into a book called The Every Other Day Diet, published in 2013.

  Her studies focus on "alternate-day fasting", in which subjects are told to consume only 500 calories one day, whatever they want the next. 

I interviewed Krista Varady at length about her research, and how modified fasting a few days of the week might help us lose weight and live longer.

How important are calories for weight loss?

They're extremely important. I've been researching nutrition for most of my life, and while some people disagree about the importance of calories, those people are typically not experts in the field. Authorities in the science of nutrition generally agree that it's calories in = calories out.  That's what modifies your weight.

The people who say calories don't matter, they generally don't have the research credentials. Other approaches like going low-carb or low-fat - or fasting in a modified way - are just different routes to achieving a calorie deficit. That's what results in weight loss, no matter what your age is.

Your book states a person can lose 12 pounds in 4 weeks with this approach; what's a realistic expectation of weight loss by fasting every other day?

I've researched only alternate-day fasting, that is restricting calories every other day to a level of about one-quarter of a person's daily caloric needs - so about 500 calories on a diet day.

Consistently, among people who need to lose 50 or 60 pounds or more, they tend to lose about 3 pounds per week. A person who's technically overweight (but not obese) tends to lose about 2 pounds per week. Someone of normal weight can lose a half-pound each week, but we don't really recommend those people try to lose weight since they're in a healthy range.

The most dramatic weight loss numbers are seen in people who are in the obese category because they tend to lose weight more quickly than others when calorie intake is reduced.

What's the potential for longevity and healthier aging - even among people who don't need to lose weight?

There hasn't been much research on the various patterns of fasting, that is, eating very little only one or two days of the week. But alternate-day fasting (eating only 500 calories every other day) has consistently shown benefits in a number of disease markers. No matter what the weight class - normal weight, overweight or obese - we see decreases in bad cholesterol, lower triglycerides, and drops in blood pressure. 

Will those changes help you live longer? We don't know yet if your true risk of mortality will drop, but these short-term clinical trials have shown that the approach lowers risk factors for age-related diseases like heart disease and diabetes.

So that means you're less likely to get those conditions, which in theory could help extend your life.

In actual longevity research, calorie restriction has been shown to extend life in animals like yeasts, worms and mice only. The general finding is that if you restrict calories by about 20%, you get about a 20% extension in the lifespan. Research on monkeys is about 10 years out, so the science isn't definitive in primates yet. It would be a very tough approach to verify in humans because the longitudinal research would take so long, and it would be next to impossible to determine the actual intake of the subjects over such a long period.

What are some of the biggest misconceptions about modified fasting?

One of the main concerns among people thinking of trying it is they worry it's a gimmick, just a gimmicky approach to weight loss. Subjects ask us, "Why not just slightly reduce the calories instead?"

Another concern people have is about skipping breakfast, since we advocate eating most of the 500 daily calories in a midday meal, along with one 100-calorie snack. People have been brainwashed to believe that they must eat breakfast! But if you dive into that research, most of it has been done on children and breakfast-skipping. A better approach is to do what's best for you. Some people find that the idea of eating food in the morning makes them nauseous. If breakfast makes you nauseous, then don't eat until later - it's not a problem!

Many people are also scared of under-eating; but we've consistently found health benefits associated with alternate-day fasting.

How safe is going down to 500 or 600 calories in a day?

Eating considerably less every second day seems to be perfectly safe. In fact, we've only seen health markers like cholesterol and triglyceride levels improve with this plan. The most common complaint is constipation; about one in ten people have this problem. We try to get them to drink more water, and exercise more. When we take a look at their food logs, we usually see that they're not getting enough fiber. Once they start consuming lots of vegetables, things get back to normal.

Really, this eating strategy mimics our ancient feasting and fasting cycles through human evolution. In caveman days, there would be a similar eating pattern: a big kill, then leaves and berries until the next big kill. That may be why our subjects don't struggle much past the first week; we've evolved to eat this way.

Why does modified fasting work for longevity, and weight loss?

For longevity, the science is fairly technical, but the research suggests that the SIRT1 gene is involved. The theory is that eating far fewer calories than your body needs creates a kind of good stress, perhaps activating genes which put your body in "cleanup mode". Instead of dealing with food, your body goes to work repairing cells and cleaning up free radicals. It's still quite hypothetical, but that's the current thinking.

For weight loss, successfully losing pounds is all about adherence. Paying close attention to what you eat every other day is simply easier for most people than deprivation every day. On a typical calorie-restricted diet, you're reducing your intake by about 20% every day; you never get to feel normal.

More to Come

Nutrition scientists are looking for the best ways intermittent fasting can promote weight maintenance, since keeping the pounds off is one of the most challenging (and traditionally least successful) aspects of any long-term plan.


Interview with Krista Varady conducted by phone January 20, 2014.

K A Varady. "Intermittent Versus Daily Calorie Restriction: Which Diet Regimen is More Effective for Weight Loss? Obesity Reviews Volume 12, Issue 7, pages e593–e601, July 2011.