Intermittent fasting (IF) is one of the newest and hottest diets to hit the fitness industry. As so often seen when something becomes popular in the fitness industry, good science is misinterpreted and misapplied. Benefits are greatly exaggerated, misapplication of the findings, and the general public gets a convoluted representation, even with sports nutrition.
What Is Intermittent Fasting?
First, IF isn't a diet. It's meal timing. You can be keto and IF, vegan and IF, IIFYM and IF, clean eating and IF; it doesn't matter.
What defines IF is it divides times of fasting and feeding into specific blocks of time. For example, the most common scheme is 16:8. This means you fast for 16 hours and eat for 8 hours and might look like:
- Eat from 10:00 AM to 6:00PM
- Fast from 6:00 PM to 10:00AM
These blocks of time can be arranged how you like. There are other more extreme blocks, such as 20:4 or even alternating days.
What Are The Benefits Of Intermittent Fasting?
IF does have some benefits. Let's look at what they are to see why people might choose it as a nutrition plan.
In the general "fitness and health" population, IF's main purpose is to lose weight. The main factors for its efficacy are calorie restriction, as people are limited to the amount of time they can eat. However, IF has also been shown to decrease calorie consumption even on non-fasting days.
IF affects our metabolic function and generally results in a greater dependence on fat for energy than carbs. This shift is believed to increase longevity and help mitigate the risk of diseases and cancers. Perhaps the most interesting benefit of IF is associated with those with pre-diabetes and insulin resistance. Due to the metabolic shift to fat, IF has been studied for its efficiency as an alternative treatment of pre-diabetes with promising results.
Does Intermittent Fasting Help With Athletic Performance?
All of the above benefits are great and useful for the appropriate population; but, is IF an effective nutrition protocol to follow if you're an athlete? Probably not. At best, studies are inconclusive. At worst, IF causes a decrease in various training variables. The main problem with finding a conclusive answer is that most studies are done on athletes following religious fasting. This fact alone shows that IF is not widely practiced in athletics as there are very few test subjects.
None of the benefits that IF boasts are specifically beneficial to athletes except being fat-adaptive will be discussed below.
Two Main Sport Nutrition Variables That Affect Performance
1) The Ratio Of Your Macronutrients
Sports nutrition is primarily based on the consumption of fats, carbohydrates, and protein. IF doesn't affect physical performance because, again, it has nothing to do with your macros. You can eat any ratio of macros from any source you want and still do IF. If you are eating too little protein, IF will not allow your muscles to repair themselves just because you're doing "intermittent fasting". Athletes still need to eat more protein regardless of IF.
In the same vain, following a high protein diet on IF can improve muscle repair but it's the high protein that helps, not IF.
2) Food Timing
The other aspect of sports nutrition is concerned with when you eat. Yes, IF tells you when you can start eating and when to stop eating. However, it says nothing about what to eat pre-workout, intra-workout, or post-workout.
For example, carbohydrate loading is a common nutrition practice to saturate glycogen stores before an event. Being on IF does not negate this. You can't be on IF and do "protein loading" and expect to have superior results.
All intermittent fasting tells us is when we can start and stop eating. That's it.
Negative Effects of Intermittent Fasting
Your performance will probably deteriorate during the initial phase of IF. This generally occurs as your body is adapting to the shift to fats for fuel. While this may subside after a month or so, it is not ideal for experimenting with in-season.
While the general public desires weight loss, it is not always beneficial to every athlete depending on their sport and position. Still, most of the studies that show IF benefiting weight loss have been on overweight individuals, not athletes.
Another risk of training fasted is the loss of muscle due to their breakdown for fuel. Athletes concerned with maintaining muscle mass and strength will find IF to be an inferior nutrition protocol.
Other negative effects that have been reported are preoccupation with food, higher perceived exertion, cognitive effects (i.e. concentration), and mood disruption.
So What About Being Fat-Adaptive?
"Fat-adaptive" is another buzzword thrown around that is often associated with IF. A common misconception of the general public is that our metabolic systems switch on and off using carbs and fat for energy. It doesn't. Our bodies are always using a combination of both; being fat-adaptive means that your body becomes more efficient at using fat for fuel, and there is a shift in percentage used towards fat.
Above we noted that IF could trigger this metabolic switch. This is beneficial for endurance athletes and general athletics alike. However, compared to the general public, athletes are already naturally fat-adaptive merely due to their higher training levels; it's not something that they need to create artificially. If you need to be more fat-adaptive, your body will do it.
Does Being "More" Fat-adaptive Help?
Thanks to the rise in popularity of keto and other low-carb diets, there has been new research on fat-adaptive athletes lately. The consensus is that; yes, athletes become more fat-adaptive when they train. However, being fat-adaptive, or "more" fat-adaptive", doesn't necessarily make you a better athlete. It's just a tremendous physiological adaptation our bodies adapt to provide more energy that naturally occurs. Excessive fat-adaption has even been found to impair your body's ability to use glycogen stores for energy.
The only time being fat-adaptive may benefit you is if you are training for prolonged times without eating, but this just doesn't (or shouldn't) happen in real life, other than athletes training during Ramadan.
What About The Professional Athletes Who Train During Ramadan?
Many of these articles have titles with "Hardcore Athletes", "Super Athletes", etc. This can make following IF during athletics attractive to impressionable young athletes. Who doesn't want to be "hardcore"? And to be honest, it is very impressive what these athletes do. They train and compete while completely fasted and are only able to drink water. That's insane.
However, fasting during Ramadan is not the same as IF. During Ramadan, these athletes train DURING their fast as they don't eat during the day. It's impressive because it's so hard to do. That doesn't sound like what an effective diet for performance should be, does it? Hard? Intense? Brutal? After researching these athletes, you see that a lot of time is spent on modifying their training just so there is no deficit in their performance. Repeat: they need to follow particular protocols so that they don't see a decrease in athletic ability, let alone an improvement.
Even with special protocols, these athletes can still see greater muscle fatigue and loss of anaerobic power, especially during the later times in their fasting blocks. Not to mention, these athletes only fast for one month and follow it for religious observance, not athletic performance.
To be clear, this is in no way criticizing fasting for religious reasons. These athletes have extreme will-power to do what they do, and it's a testament to their faith. However, it won't bring you any benefits in athletic performance.
Intermittent Fasting For Athletic Performance
This brings us to a common problem we touched on in the beginning. A diet that is beneficial for a specific population DOES NOT mean it's advantageous to every population. Yes, IF can help you lose weight and possibly become more fat-adaptive, but neither translates into becoming a better athlete (not to mention you can do both without IF).
There aren't enough studies to cover every little caveat of IF. Just a few examples to illustrate how this answer can be muddled.
- • If you are eating from 10 AM-6 PM with appropriate macros, you could probably perform just fine.
- • If you are alternating days of eating, you're going to suffer.
As of now, what we do know is that the vast majority of studies on IF and performance have come up with two conclusions:
- There are no improvements in athletic performance
- There's a negative effect on athletic performance
Neither sounds ideal when trying to improve performance.
- Why Intermittent Fasting Is Unsuitable for Athletes
- 6 Questions to Ask Yourself Before Trying Intermittent Fasting
- Intermittent Fasting: Secrets of Success