Intermittent Fasting: Who’s It For? (And, if It’s Not for You, What to Do Instead)


John Berardi, Ph.D. HuffPost

Intermittent fasting (IF) may sound technical. But all it really means is going for extended periods without eating.

Why would anybody want to do that? Well, a growing number of fitness experts claim that the practice can help people lose fat and improve their health.

But intermittent fasting is hardly the exclusive preserve of nutrition nerds. In fact, we all do some form of it every single day. Except we don’t call it that. We call it sleeping.

That’s right. The time from your last meal at night until your first meal the next day could be described as a “fasting” interval.

(And the time from your first meal of the day until your last meal can be called a “feeding” interval.)

It’s as simple as that. So try not to get too entranced by the terminology.

In the end, people who decide to practice intermittent fasting simply extend the length of time when they are not eating.

Of course, everyone’s jockeying to “get it right.” Which means many different protocols have emerged — Eat Stop Eat, Leangains, the Warrior Diet, the 5:2 diet, and more — but in one way or another, all of these plans shrink the “eating” window and expand the “not eating” window.

What’s the point of fasting?

Although the name may be a recent invention, intermittent fasting is nothing new. In fact, humans have always fasted, whether just overnight, during more extended periods of food scarcity, or for religious reasons.

What is new is that clinical research on IF’s benefits for health and longevity is beginning to catch up.

Data suggest that IF, when done properly, might help extend life, regulate blood glucose, control blood lipids, reduce the risk of coronary disease, manage body weight, help us gain (or maintain) lean mass, reduce the risk of cancer, and more.

Now, these studies are still in their early stages, so there’s plenty of room for skepticism. Still, some of the findings look promising.

That’s why many people in the fitness world have decided to put IF to the test. In the absence of hard data, they’re opting for personal experimentation.

Including me.

I’ve even written a book about my own self-experiments with intermittent fasting. You can access it, completely free, by clicking here.

The CliffsNotes version? I lost weight and body fat, maintained lean mass, and managed to do this in a way that felt sustainable. Success!

But intermittent fasting is not for everyone

While intermittent fasting worked for me, it is not a good fit for everybody.

First of all, intermittent fasting is not just another way of saying “free ride.” Randomly skipping meals while continuing to eat a diet high in processed foods won’t help you lose fat or improve your health.

So while there’s no one “right” way to practice fasting, any decent protocol will involve a certain amount of attention to nutritional specifics. You have to be prepared to do that work.

Some will find IF too inconvenient or troublesome to practice. And for others, its risks far outweigh any potential benefits. In fact, for some people IF could be downright dangerous.

Before you skip your next meal, you probably want to know whether you fall into that category.

Here’s the lowdown, based on numerous case studies and a small amount of published research.

Intermittent Fasting: Green Light

In my experience, you’re most likely to be successful with intermittent fasting if:

  • you have a history of monitoring calorie and food intake (e.g., you’ve “dieted” before)
  • you’re already an experienced exerciser
  • you’re single or you don’t have children
  • your partner (if you have one) is extremely supportive
  • your job allows you to have periods of low performance while you adapt to a new plan
  • you’re male

The first five factors will allow you to build the protocols into your lifestyle more easily, while the final condition (being male) seems to affect results.

Intermittent fasting: Yellow Light

Meanwhile, if you meet the following criteria, you may want to proceed with caution:

  • You’re married or have children
  • You have performance oriented or client-facing jobs
  • You compete in sport/athletics
  • You’re female

Again, the first three conditions make it much harder to follow IF protocols and may make it impractical for you. What’s more, trying to fast may conflict with performance goals for your sport.

As for the last condition, some experimenters suggest that for women, fasting causes sleeplessness, anxiety, irregular periods, and other indications of hormone dysregulation.

In particular, women seem to fare worse on the stricter forms of intermittent fasting than men do. So if you’re female and you want to try fasting, I recommend beginning with a very relaxed approach.

Intermittent Fasting: Red Light

Finally, there are some people who really shouldn’t bother with intermittent fasting at all. Don’t try it if:

  • You’re pregnant
  • You have a history of disordered eating
  • You are chronically stressed
  • You don’t sleep well
  • You’re new to diet and exercise

If you’re new to diet and exercise, intermittent fasting might look like a magic bullet for weight loss. But you’d be a lot smarter to address any nutritional deficiencies before you start experimenting with fasts. Ensure you’re starting from a solid nutritional platform first.

Pregnant women have extra energy needs, so if you’re starting a family, this is not the time to fast.

Ditto if you are under chronic stress and/ or not sleeping. Your body needs nurturing, not additional stress.

And if you’ve struggled with disordered eating in the past, you probably recognize that a fasting protocol could lead you down a path that might create further problems for you. Why mess with your health? You can achieve similar benefits in other ways.

Not a fit for you? How to get in shape without intermittent fasting

How can you get in shape and lose weight if intermittent fasting isn’t a good option for you?

Learn the essentials of good nutrition. It’s by far the best thing you can do for your health and fitness.

Cook and eat whole foods. Exercise regularly. Stay consistent. And if you’d like some help to do all of that, find a mentor or coach.

Heck, that last part is relevant even if you decide to try intermittent fasting.

While self-experimentation is good, guided experimentation is even better. Especially when it’s overseen by an experienced coach.

Want some help finding the best diet for you? Download this free guide: Paleo, vegan, intermittent fasting… Here’s how to choose the best diet for you.

About the author

John Berardi, Ph.D. is a founder of Precision Nutrition, the world’s largest online nutrition coaching company. He also sits on the health and performance advisory boards of Nike, Titleist and Equinox.

Dr. Berardi was recently selected as one of the 20 smartest coaches in the world by, the internet’s most popular fitness site.

In the last five years, Dr. Berardi and his team have personally helped over 30,000 people improve their eating, lose weight, and boost their health through their renowned Precision Nutrition Coaching program.


Azevedo, F.R., et al. Effects of intermittent fasting on metabolism in men. Rev Assoc Med Bras. 2013 Mar-Apr;59(2):167-73.

Klempel et al. Intermittent fasting combined with calorie restriction is effective for weight loss and cardio-protection in obese women. Nutrition Journal 2012, 11:98

Kroeger et al. Improvement in coronary heart disease risk factors during an intermittent fasting/calorie restriction regimen: Relationship to adipokine modulations. Nutrition & Metabolism 2012, 9:98.

Stipp, David. How Intermittent Fasting Might Help You Live a Longer and Healthier Life. Scientific American, Vol. 308/1, 2012.



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