Fasting every other day – worth a try?

Red apple sitting on the calendar.The question at hand today is whether fast every other day is a viable, perhaps even preferable option for people who want to experiment with intermittent fasting. I’ve written about fasting here on the blog many times because it’s one of my favorite tools for controlling insulin, blood sugar, appetite, and (possibly) promoting longevity, but I’ve never devoted a post to fasting every other day per se. Time to fix that.

I call it an aid, but fasting – with regular, marked periods of little or no food – is the natural human condition. Or at least it should be. As I like to say, physiologically speaking, the best things happen when we don’t eat. Fasting induces desirable hormonal responses, reduces oxidative damage, promotes autophagy, and provides a mental challenge. Of course, in today’s nutrient-rich environment, most people regularly eat for more than 16 or 18 hours a day. Eating in a 6 or 8-hour window, let alone without food for 24 hours or more, is rare.

For the most part, I am agnostic about the optimal fasting schedule. Whether one prefers time-restricted eating such as the popular 16:8 or 18:6 protocols, a weekly 24-hour fast, six-monthly extended fasts of three days or more, or eating WHEN (when hunger develops naturally) is a matter of personal taste. They all have pros and cons, but none are so compelling that I’d say one is clearly best for everyone. Since many people seem to be inclined to fast every other day, it deserves a closer look here.

What exactly is intermittent fasting?

There are two broad categories of every other day fasting (ADF):

Real ADF is where you skip food all day. Eat one day, don’t eat the next. Simple, not necessarily easy. This type of automatic document feeder requires you to fast for 36 hours every other day (dinner one day to have breakfast two days later). Maybe even longer.

Modified ADF is where you eat every day, but alternate between days when you eat normally and days when you significantly restrict calories. The general rule is to consume 25 percent of your typical daily calories. If you normally eat 2,400 calories, your week will look like this:
Day 1: 2,400 calories
Day 2: 600 calories
Day 3: 2,400 calories
Day 4: 600 calories
Day 5: 2,400 calories
Day 6: 600 calories
Day 7: 2,400 calories

Everything else is allowed. You can combine ADF with any diet – Primal, Keto, Vegan, Carnivore, even SAD (although I wouldn’t recommend it for obvious reasons). There are no rules about when or how often you eat on your normal eating days, but the idea is to consume the same number of calories you would eat for weight maintenance, maybe a little more. Assuming you don’t go wild, you’ll end up with a pretty hefty calorie deficit, even if you eat normally half the time.

There are also a few specific variations in ADF:

  • 5:2 fasting is probably the most famous. This is similar to modified ADF, but instead of eating a deficit every other day, choose two days a week, usually non-consecutive, to limit calories.
  • Eat Stop Eat, the brainchild of Brad Pilon, is a type of modified ADF where you do one or two 24-hour fasts a week. Once or twice a week, you eat dinner one day and then dinner the next day (or breakfast to breakfast, lunch to lunch, whichever you prefer).
  • The Every Other Day Diet was conceived by Krista Varady, PhD, currently a professor of kinesiology and nutrition at the University of Illinois, Chicago, and the author of dozens of scientific papers on the subject of fasting, plus a popular book of the same name. This is your typical custom ADF approach with one notable difference: you can eat ad libitum (as much as you want) on meal days. According to Varady, most people still end up in a calorie deficit and lose weight even with “holidays.” Some readers of her book, The Every Other Day Diet, disagree. However, she has proven to have success with this method in her academic work.

Benefits of Fasting Every Other Day

Possible benefits of ADF include:

  • Lower fasting insulin (but inconsistent effects on insulin sensitivity)
  • Lower triglycerides (plus LDL and total cholesterol if you go for that)
  • Low bloodpressure
  • Reduction of adipokines implicated in systemic inflammation and cardiovascular disease
  • Promote ketosis

If it sounds like I’m hedging my bets here, it’s because there’s no standardization with how researchers use the term “alternative day fasting.” There is a lot of promising data, but it is difficult to generalize from one study to another when one uses an Eat Stop Eat design and the other uses 5:2 with two consecutive fast days. The metabolic effects may not be the same.

Researchers are also still trying to figure out whether the benefits are unique to fasting or whether they are primarily due to the calorie restriction inherent in these types of fasting protocols. It’s a very open question at this point, although I suspect fasting is more than just calorie restriction.

What about weight loss? Can Fasting Every Other Day Help You Lose Weight?

Yes. This has been demonstrated in multiple studies with different styles of ADF and different populations. Not to mention all the anecdotal evidence.

The more interesting question is, are you likely to lose? Lake weight – or lose weight more easily – with ADF. The available studies seem to suggest that while you can lose more weight in the short term with ADF, fasting and regular calorie restriction diets (also known as “continuous calorie restriction”) eventually become more even if the calories are matched. As for ADF, compared to other types of fasting, such as time-limited daily eating, there aren’t enough cross-sectional studies to draw any conclusions one way or the other.

“But wait,” you say, “I couldn’t lose weight when I tried dieting until I started fasting.” I hear this a lot. Just because ADF doesn’t have a strong weight loss benefit on average doesn’t mean it wasn’t beneficial for you. When it comes to losing weight, diet tracking plays a huge role. Many people find it easier to stick to a schedule where they don’t have to limit food every day.

Disadvantages of fasting every other day?

To do ADF properly, you need to track your food, which can be tricky. People who don’t want to weigh and measure every bite can try the Eat Stop Eat approach, which doesn’t limit what you can eat on your fast days (or, more precisely, at the end of your 24-hour fast).

It’s also not easy to eat just 500 or 600 calories, especially if you want to break it down into multiple meals or snacks. You’ll want to limit fat intake, as fat is the most calorie-dense macronutrient at nine calories per gram. Once you factor in enough protein, there’s little room for anything else. I suggest eating only one or two meals on fasting days and eating low-calorie, non-starchy vegetables such as leafy greens. Sipping bone broth can also help satisfy hunger, but there shall feeling hungry, especially in the beginning.

One possible concern is the maintenance of lean body mass. In four studies of overweight/obese adults, dieters lost, on average, more lean body mass with ADF than with continuous calorie restriction (regular diet). These studies ranged from 12 to 30 weeks and the participants ate a fair amount of protein. However, none of the studies provided exercise instructions, and it’s not clear whether any of the participants took any resistance training.

Bottom Line: Alternative Day Fasting Yes or No?

Overall, the benefits of ADF seem to be consistent with the benefits of fasting in general. As far as I can see, the biggest advantage of ADF over daily time-restricted eating or calorie-restricted diets is that some people find it easier to stick to.

The findings regarding lean body mass give me pause, but not enough to write off ADF at this point. While the four studies were fairly consistent, there was also a lot of variability between participants. When you eat with an energy deficit, you want to make sure you eat plenty of protein and lift heavy things to protect your muscles. That is simply the best habit, no matter what type of fast you do. That said, the strict ADF I outlined above puts you in a 33 percent energy deficit, which is quite significant — perhaps too large to be safely sustained long-term. We could use more human studies here to tease all this out.

And speaking of best practices, what you eat during your non-fasting days matters. While ADF doesn’t strictly require it, it just makes sense to eat the same nutrient-rich, whole foods whether you’re on ADF or not.

Finally, the same rules apply to those who are not allowed to fast: people who are already overloaded and those with high energy needs such as competitive athletes, children and teenagers, and those who are pregnant or breastfeeding.

Okay, guess what? Yes or no, are you interested in fasting every other day? If you’ve already tried it, how did it go?

Related posts from Mark’s Daily Apple

How intermittent fasting and what type of fast is right for you?

The Myriad Benefits of Intermittent Fasting

Fasting vs. Carb Restriction: Which Works Better for Which Scenarios?

7 Tips and Considerations for Eating One Meal a Day


About the author

Mark Sisson is the founder of Mark’s Daily Apple, godfather of the Primal food and lifestyle movement, and the… New York Times bestselling author of The Keto Reset Diet† His latest book is Keto for life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is also the author of numerous other books, including: The original blueprintwhich in 2009 had boosted the growth of the primal/paleo movement. After spending three decades researching and educating people about why food is the most important component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that makes Primal/paleo, keto, and Whole30. -friendly kitchen staples.

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