Intermittent Fasting For Athletes: The Why and How

In this article, the two forms of fasting I will breakdown for you are Full day fasts (FDF) and daily fasts. I will discuss the pros and cons of each, and how it can be directly applied to athletes.

The intermittent fasting craze is here. We’ve all heard about how awesome it is for body composition goals, but what about for athletic performance? It seems like the only athletes who are practicing fasting are the ones doing it for religious reasons. Now is the time for change. I’m telling you so: all athletes can practice some sort of intermittent fasting and reap the benefits from it.

Personally, I’ve been practicing various forms with myself and my clients. While it’s generally pretty great, I have found it isn’t for everybody. In this article, the two forms of fasting I will breakdown for you are Full day fasts (FDF) and daily fasts. I will discuss the pros and cons of each, and how it can be directly applied to athletes.

Full Day Fast (FDF)

Full day fasts are when you abstain from eating for a 24-hour period. For example, let’s say you eat your last meal on a Saturday at 10:00pm; the next time you would eat would be at 10:00pm on Sunday. During these food-free 24 hours, your body will experience benefits such as higher growth hormone levels, detoxification of the liver, decreased inflammation, and a lower weekly caloric intake (obviously).

The purpose of including a full day fast is to help your body to recover from the week’s mini-injuries and joint pain. It is also very beneficial for athletes who are in weight classes and need to maintain a low body weight or low body fat levels.

During the FDF, your body needs to relax. This means minimal activity (walking, enjoying yourself outside, etc.), and all the naps you desire. When you are not relaxing, I often recommend trying to keep busy, as your mind will be laser sharp and productive. Also, keeping busy is a great way to shroud the thoughts of food from your mind.

The only problem with FDFs is they are sometimes too effective at keeping your bodyweight low. This means some athletes may see their body weight drop too rapidly. Sometimes, too much of a good thing is a bad thing.

How to do it:

When incorporating FDFs into your eating schedule, I only recommend including them once every seven days. The reason behind this is because athletes are generally very active, and you need to allow minimal activity during FDFs. Since all athletes should have at least one full rest day per week, the FDF and a weekly full rest day go hand-in-hand. When breaking the FDF, it is best to have one small meal consisting of fat and vegetables. This will ensure that you ingest minimal calories, keep insulin, low, and allow your body to use the fat as energy.

Who it’s for: Weight class athletes, martial artists, sprinters, endurance athletes

Who it’s not for: Football linemen, athletes who have a hard time keeping weight on

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Daily Fasts

When most people think of daily fasts, Martin Berkhan’s LeanGains comes to mind. Berkhan’s proposal of a 16-hour fast followed by an 8-hour eating window is excellent for athletic performance, although the main reason may not be the one that you initially believed. During daily fasts, the laser sharp focus your brain experiences should be taken advantage of and used for increased concentration during sports or even weight training. This translates to improved performance such as fewer errors, quicker reaction times, smarter choices, and (in some cases) quicker strength gains.

How to do it: 

I recommend skipping breakfast daily and break your fast 6-8 hours after you wake up. The reason for this is that it is easier to fall asleep at night if you are satiated rather than hungry. More sleep translates into better recovery. If you have sports practice during the fasting period, it is definitely advised to supplement with branched chain amino acids (BCAAs).

Depending on your body size and the intensity of your sport, I recommend the following dosages:

  • Before practice: 5 g of BCAAs
  • During practice: 5-10 g of BCAAs
  • After practice: 5-15 g of BCAAs

If you have a game or competition during your fasting period, then there are a few different rules. Since the nature of the competition is generally more intense (physically, mentally, and hormonally), you will need to ingest a small amount of calories into the body. This can be achieved with both BCAAs and a simple sugar (such as dextrose).

The following dosages are recommended:

  • Before practice: 5 g of BCAAs
  • During practice: 5-10 g of BCAAs, 25-75 g of dextrose
  • After practice: 5-15 g of BCAAs, 50-150 g of dextrose

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These dosages are recommended for all athletes except the ones who participate in endurance sports (long distance running, triathlon etc.). Competing in endurance sport during the fast is highly contraindicated. As you may know, endurance activity yields a need for immediate energy. During the fast, your body converts stored body fat into usable energy. It is a slow, but efficient process. Although this is usually beneficial, endurance sports demand a quicker method of obtaining energy. This method comes from digesting food.

Who it’s for: Athletes who could benefit from increased concentration and focus

Who it’s not for: In-competition endurance athletes


In conclusion, FDFs are great for maintaining a lower bodyweight, while daily fasts contribute to increased focus and performance on the field and in the weight room. If you have the willpower, give intermittent fasting a try and you will reap the benefits that both methods have to offer.

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