Intermittent Fasting For Endurance Athletes, Should You Follow It?

intermittent fasting for endurance athletes

Intermittent fasting (IF), along with keto diet has exploded as a weight loss solution for the last few years. Just like any other diet, it has its own pros and cons. For a sedentary person, it can be an effective way to stay healthy but is it the right choice for endurance athletes?

It is health that is real wealth and not pieces of gold and silver. – Mahatma Gandhi

The answer is, it depends. Is there any correlation between intermittent fasting and performance improvement? Not really. In fact, done poorly, it can adversely affect your performance and progression. If so, why everyone’s doing it? Is it only about weight management? Raises a lot of questions, isn’t it?

Let’s briefly go through the concept of intermittent fasting first, especially for those who are not aware of it.

IF is a dietary concept where we abstain from eating for various amounts of time, for example on a daily or an hourly basis. In essence, we set a specific eating window to consume our daily nutrition requirements.

You may ask what’s the difference between fasting in Ramadan and IF. There are various types of fasting and the one we practice in Ramadan is called Dry fasting, where we refrain from consuming both liquids and foods. In intermittent fasting, you can have water or any zero calorie liquids.

intermittent fasting what really is

The three most common IF plans are the 16:8 plan, the alternate-day plan, and the 5:2 plan. The 16:8 plan requires 16 solid hours of fasting every day followed by 8 hours of eating window. The alternate-day fasting means exactly what it reads, IF on alternate days. Finally, the 5:2 plan requires 2 consecutive IF days followed by regular eating days in the week.

To any average person, the idea of athletes skipping meals may sound like madness as high performance requires high energy reserves. So, if you are thinking of starting IF to become a faster athlete, think again. It’s not going to IMPROVE your performance but sure there will be some positive physical adaptations.

What exactly can Intermittent Fasting offer to the athletes?

Intermittent fasting helps to develop your focus more

You’ll be able to focus on your work life, social life, etc. even though you’re starving for food. In fact, it’s scientifically proven that intermittent fasting helps your brain to think with clarity and improves the attention span. As an athlete, there will be difficult situations during a race or in a daily routine where you’ll be forced to continue without eating anything. This added focus shall help you navigate the situation without bonking.

Healthy and a strong stomach

We often forget that our stomach has to work a lot to break down the foods that we eat. When we constantly shove food in our stomach, it has to work overtime. If the stomach becomes sensitive and weak, you’ll struggle to eat anything comfortable and the food choices can become very limited.

Now imagine that you’re in a race and you can absorb anything easily. Will it not make your life easier? A strong gut is definitely an asset for athletes. Scientists say that proper fasting is really good for the stomach. In fact, most major religions enforce fasting for a specific period of time. Coincidence?

Maintaining metabolism

The biggest issue of crash dieting is it slows down the metabolism a lot hence when you start eating normally, you gain weight even quicker. Slow metabolism also slows down energy expenditure. You could spend the week restricting calories each day or use fasting to arrive at the same weekly caloric load and the effects will be different.

For an athlete, chronic calorie restriction spells doom as athletes need to be able to expend energy when they need it. Luckily, studies show that intermittent fasting is one way to “reduce calories” without reducing energy expenditure. Perhaps the main reason is that IF doesn’t necessarily lower calories; it just changes the time when you get them.

Improving metabolic flexibility

Metabolic flexibility is the ease with which a person is able to switch between sources of energy—from carbs to fat and back again. Intermittent fasting improves metabolic flexibility and promotes more fat burning. For an athlete who interested in health, and longevity; metabolic flexibility is absolutely essential.

If you’re metabolically flexible, you can burn fat for longer before switching over to carbs. You can burn carbs when you actually need them, right away. And afterward, you can switch back into a passive fat-burning mode to keep unnecessary carb cravings.

intermittent fasting negatives

But what are the cons?

So far, it sounds all good to you, isn’t it? But as I keep reminding, poorly done, it has negative consequences as well. Let’s see how it can affect you as an athlete.

Recovery becomes difficult

You only become faster when you recover from hard workouts, not doing more workouts. Athletes do need to eat more than an average person. To promote recovery, enough carb and protein are required before and after training sessions. Muscular inflammation can persist longer if the IF plan doesn’t fit with the daily lifestyle.

Also, since the eating window is smaller, athletes will need to cram in all the daily requirements within that time. For some people, eating too many foods within a short period of time can be cumbersome.

Wrong timing, the wrong outcome

The problem is if you time it improperly or apply intermittent fasting more frequently than you should, you can easily burn yourself up. Not eating before a HIIT session will reduce your training performance and can hinder your overall training plan.

Also, if you have more than one training session daily, as many multisport athletes do, intermittent fasting could make it harder to consume food both before your first session and after your second session.

May reduce testosterone

Testosterone is vital for male athletes to improve performance, strength, and general vitality. Unnecessary IF can reduce testosterone levels and can impact muscular loss, lower recovery as well as weight gain.

Losing benefits of frequent eating

For athletic performance, a free eating pattern is beneficial according to some of the studies. Regular intakes of protein spaced throughout the day are better than larger intakes consumed less often. While the impact might be small, it could make the difference for athletes, and intermittent fasting would preclude this.

intermittent fasting breakfast skipping


As an athlete, if your goal is to lose weight or to improve physical adaptation, then sure go ahead with IF. Generally speaking, eating less may be a good long-term strategy. A chronically lower-calorie lifestyle may be associated with a longer lifespan. If fasting fits your long-term lifestyle, and it makes you feel good, then go for it.

To achieve better performance though, fasting is never an optimal strategy. If you want to integrate IF in your schedule, make sure that it fits with your goal without compromising performance. I would definitely prefer IF over a Keto diet anytime. You may need to tinker with the eating window though and I hope to write another article on that.

Just, don’t start intermittent fasting for performance gain, please.

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