How Alternate-Day Fasting Can Help You Achieve Your Weight Loss Goals

By Joseph Mercola,

You don’t have to diet every day to lose weight. This compelling concept is the focus of Dr. Krista Varady’s book The Every-Other-Day Diet: The Diet That Lets You Eat All You Want (Half the Time) and Keep the Weight Off.

Dr. Varady is an associate professor of nutrition at my alma mater, the University of Illinois in Chicago, and in this interview, she reveals how intermittent fasting can help you achieve optimal health and weight without starving yourself every day. She explains what prompted her to investigate, and eventually write a book on this topic.

“I wanted to do a PhD in the area of calorie restriction and fasting,” she says. “I wanted to find out: do you really have to diet every single day to lose weight? I noticed that people just weren’t able to stick to calorie restriction programs for more than about a month or two. Everyone dropped off of their diet.

I thought: ‘is there a way to manipulate that eating pattern that will allow people to stick to it longer? Maybe you could diet every other day?’ That way you can always look forward to the next day, where you can eat whatever you want. Maybe that would help people kind of stick to these diets?”

As it turns out, her hunch was correct. Alternate-day fasting has a far greater retention- and compliance rate compared to conventional all-day fasting regimens. My preferred version of intermittent fasting, which simply calls for restricting your eating to a narrower window of about six to eight hours or so each day, also has a far greater success rate than more extensive fasting protocols.

Complete Versus Intermittent Fasting

Complete fasting is when you consume nothing but water for 24 hours, midnight to midnight, at regularly recurring intervals. This kind of calorie restriction has well-documented health benefits, including life extension, but the compliance rate for this kind of program is low. It’s just too severe for the vast majority of people.

Intermittent fasting is an umbrella term that covers a wide array of fasting schedules, including the 5:2 approach. As a general rule however, intermittent fasting involves cutting calories in whole or in part, either a couple of days a week, every other day, or even daily, as in the case of the scheduled eating regimen I use myself.

Dr. Varady’s research shows that alternate-day fasting, where you consume about 500 calories on fasting days and can eat whatever you want on non-fasting days, works equally well for weight loss as complete fasting, and it’s a lot easier to maintain this type of modified fasting regimen.

In her study, which was recently completed, participants ate their low-calorie fasting day meal either for lunch or dinner. Splitting the 500 calorie meal up into multiple smaller meals throughout the day was not as successful as eating just one meal, once a day.

The main problem relates to compliance. If you’re truly eating just 500 calories in a day, you will lose weight. But when eating tiny amounts of food multiple times a day, you’re far more inclined to want more, so the cheat rate dramatically increases.

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What About Alternate-Day Fasting?

Alternate-day fasting is very much in alignment with Paleo perspectives that seek to replicate the behaviors of our ancient ancestors to optimize health. In our ancient past, people did not have access to food around the clock. They would cycle through periods of feast and famine, which modern research shows actually has biochemical benefits.

The reason so many struggle with their weight (aside from eating processed foods that have been grossly altered from their natural state) is because they’re in continuous feast mode and rarely ever go without a meal. As a result, their bodies have adapted to burning sugar as its primary fuel, which down regulates the enzymes that utilize and burn stored fat. Fasting is an excellent way to “reboot” your metabolism so your body can start burning fat as its primary fuel, which will help you shed your unwanted fat stores.

“It takes about a week to 10 days or so to get used to that up-down pattern of eating,” she says. “But it’s amazing. Even though people struggle through the first week, they always say, ‘After a week, I had no problem eating just 500 calories every other day.'”

Tips for Making It Through the Transition Period

The toughest part, of course, is getting through that initial transition, which can be anywhere from seven to 10 days. Maybe even longer for some people, depending on how insulin-resistant you are, and other factors, like your weight, blood pressure, and cholesterol levels, and if you are not consistent with the fasting and wind up cheating.

About 10 percent of people will report headaches as a side effect when they first start fasting, but the biggest complaint is feeling hungry. It may be helpful to remember that part of why you’re craving food is because your body has not yet fully switched from burning sugar to burning fat as its primary fuel. Sugar is a fast-burning fuel, whereas fat is more satisfying. As long as your body is using sugar for fuel, it will “remind” you that it’s running low and needs a refill at regular intervals. So part of the challenge is getting through that transition period. Another factor is purely psychological. As Dr. Varady explains:

“Many people are just used to eating constantly. Not only is it actual hormonal responses, but I think it’s just habit… Most people eat just because they’re bored. I think a lot of it is psychological—that’s what takes people a while to get used to. In terms of helping people get through that, we always recommend drinking a lot of water (eight to 10 extra glasses of water a day). Because people will often think that they’re hungry, but really they’re thirsty…

We also tell people to watch less television. You don’t realize how bombarded you are with food commercials; something like 60 percent of commercials are about food. That’s why most people will end up getting a snack within half an hour when they’re sitting down and watching TV.”

The vast majority of Americans are overweight and most would therefore benefit from this type of eating regimen (adrenal-fatigued individuals are perhaps an exception to this rule). When done correctly, you will inevitably lose weight and your insulin and leptin receptor sensitivity will be optimized, which is really important for optimal health. The next question then becomes, do you have to continue on indefinitely with this alternate-day fasting schedule?

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How Long Must You Remain on an Alternate-Day Fasting Schedule?

Dr. Varady is currently investigating this question through a study funded by the National Institutes of Health (NIH). The study is set up to be a year long, with six months of weight loss through alternate-day fasting, followed by six months of weight maintenance. She’ll compare the results against a traditional approach of calorie restriction and traditional weight maintenance where you eat just 100 percent of your energy needs every day.

“We’re almost done with the study,” she says. “What we’re noticing now is that people can use every-other-day dieting for weight maintenance. However, you need to tweak it a little bit in that you reduce the fasting days down to three days per week, and instead of consuming 500 calories on each of those days you’d consume 1,000… In terms of comparing it to daily calorie restriction, it actually does a little bit better. People in the every-other-day dieting group were actually able to maintain their weight a little bit better than people doing a traditional maintenance approach. “

So, it appears you do have a bit more flexibility once you’ve reached your weight loss goal. In terms of what to eat, Dr. Varady’s book ultimately advocates transitioning into a Mediterranean-type diet.

“We do want people to slowly change their eating habits. But we find that if we kind of overwhelm people with not only the ‘eat 500 calories every other day’ but then tell them to change all their dietary patterns right away, people quit the diet and tend to do nothing,” she says. “It’s good if you can just start the actual up-down approach of eating, just the 500 calories every other day, and then slowly transition into whole foods and basically healthier foods.”

So in summary, you don’t have to keep on intermittently fasting forever if this is a lifestyle strategy that doesn’t appeal to you long-term. If you need to lose 50 pounds, you’re looking at about six months or so of intermittent fasting, after which you can revert back to eating more regularly. I strongly recommend paying careful attention to your food choices, however. Even on non-fasting days, I believe it’s important to eat a diet that is:

  • High in healthy fats. Many will benefit from 50-85 percent of their daily calories in the form of healthy fat from avocados, organic grass-fed butter, pastured egg yolks, coconut oil, and raw nuts such as macadamia, pecans, and pine nuts
  • Moderate amounts of high-quality protein from organically raised, grass-fed or pastured animals. Most will likely not need more than 40 to 80 grams of protein per day.
  • Unrestricted amounts of fresh vegetables, ideally organic