Intermittent fasting (IF) is the solution to all your problems. It will help you stay lean without losing strength and it will cure all your diseases. It makes you a superhuman! Not only that, you can eat crappy food and stay strong!
 
If you are an athlete, coach, or simply on a quest to get and stay healthy, you have probably heard some version of the above. But hopefully, you didn’t fall for these misleading, exaggerated statements.
 
While IF isn’t the magic bullet many people make it out to be (there isn’t a magic bullet, by the way!), that doesn’t mean it isn’t useful and doesn’t have its place in certain situations. This article will review what IF is and if there is any science to back up its promoted effectiveness so we can determine if it may be beneficial for strength athletes.
 
What is IF?

In the nutrition industry, the term IF refers to multiple types of nutritional interventions including:
 
True fasts (aka. IF)
·       Greater than or equal to 24 hours of pure fasting (water allowed).
·       Typically, they do not extend greater than 7 days.
·       Implemented in a variety of ways.
o   Alternating day fasts.
o   24-hour fast once per week or month or quarter, etc.
o   36-48 hour fast once per month or quarter or semi-annually, etc.
o   5-7 day fast semi-annually or annually.
 
Time-Restricted Eating (TRE)
·       The fasting window is less than 24 hrs and can be implemented daily.
·       Implemented in a variety of ways:
o   12-hour fast with 12 hour eating window
o   13 to 16-hour fast with 8 to 11 hour eating window
o   Only eating one meal per day
 
For this article, I will use the terms IF and TRE based on the above definitions.
 
IF Versus Caloric Restriction
 
While they can overlap, IF and chronic caloric restriction are not the same. Caloric restriction refers to limiting calorie consumption for long periods while most IF methods do not lead to long term calorie restriction, aside from ongoing alternating day fasts.
 
The reason IF and TRE have gained popularity is that they are thought to mimic the benefits of caloric restriction without the need to chronically restrict calories, but consider this. While there is plenty of evidence in insects and rodents that caloric restriction increases life span, there is no evidence that this is the case for humans. Furthermore, these effects are only measured in laboratory environments, not natural environments where animals would eat and live the way they evolved. Therefore, there is a strong argument that caloric restriction may not extend the life of free-living animals. Prolonged caloric restriction can also have negative effects such as reduced muscle mass, reduced bone density, reduced physical performance, hormonal disruptions, low energy, nutrient deficiencies, etc. In light of this information, the question is whether it is smart for athletes to consider IF or TRE?
 
Healthy Nutrition Is Always a Must
 
Before we proceed, I must make one thing extremely clear. There is no nutritional, exercise, or other intervention that negates the detrimental effects of a terrible diet. And yes, this even applies to IF and TRE. A recent study showed that there was no difference between TRE and normal schedule eating when subjects were advised not to change the contents of their normal diets, just the schedule of when they ate. So, no matter what your goal, the first step is to learn how to eat a healthy, whole-food diet. Vegetables, meat, fish, fruit, nuts, and seeds should make up the bulk of anyone's diet. It is assumed that before an athlete considers IF or TRE, they are already eating a dialed-in whole food nutrition plan…period!
 
IF and Athletes
 
To be quite frank, IF is not appropriate for darn near any athlete when they are actively training or competing. That being said, there are always outliers and exceptions to everything.
 
Limited studies are available that focus on IF in athletes, they are focused on endurance athletes, the results are not consistent, and they show that performance is reduced after fasting of greater than 24 hours. While one study found an increase in endurance performance, endurance athletes are not the same as strength athletes, the subjects lost about 3 percent of their muscle mass, and the authors admitted that long term caloric restriction would lead to micronutrient deficiencies. Ultimately, there is no scientific evidence to support IF for strength athletes as the risk of nutrient deficiency and decreased performance is too high.
 
Yes, there are exceptions to the above. Evidence on IF in humans does indicate that it can reduce markers of metabolic syndrome. This includes weight loss, reduced fat mass, improved cholesterol levels, reduced inflammatory markers, and reduced insulin levels/insulin sensitivity. These are all great things for those in the general population that are overweight and/or have metabolic syndrome. Most athletes do not fall into this category, although there are some. So, for athletes in these categories, IF could be a helpful dietary intervention to use during an “off-season” with the help of a nutrition professional. Just remember, many dietary interventions can be helpful for weight loss and metabolic syndrome based on individual preference. Some people may find IF easier than counting calories or portion control or a low carbohydrate/ketogenic diet, while others may not.
 
What about sports with weight classes? Hopefully, you know that cutting weight is not the same as losing weight. Cutting is temporary and rapidly achieved while losing weight is permanent and gradually achieved. IF can be effective for weight loss in obese and overweight individuals, however, it is not effective for rapid weight cutting for weigh-ins.
 
TRE and Athletes

While IF comes with the significant risk of caloric restriction TRE does not, at least when done properly. TRE simply means restricting your eating to a smaller window of time in 24 hours. The argument is that during the fasting period we can get some of the benefits of IF/caloric restriction without reducing our daily caloric intake.
 
Regardless of what you hear in the gym, from your coach, from your friend, or even from a nutrition professional, there is a very limited amount of studies in humans looking at TRE and strength/high-intensity training. Specifically, there are approximately 5 human studies on this topic, 1 of them focuses on strength training in a group of novice lifters, 1 of them focuses on intermediate lifters (< 1 year of lifting), 1 of them focuses on strength training in a group of experienced lifters (not Olylifting), 1 of them focuses on professional bodybuilders, and 1 focuses on power athletes (sprinters, wrestlers, throwers).
 
Two of the studies on lifters implemented controlled TRE programs that attempted to ensure adequate caloric intake during the 8-week studies. One study used a 20-hour fasting window while the other used a 16-hour fasting window. Only one of the studies reported that subjects were able to intake adequate calories yet both studies reported that strength and muscle size were maintained.
 
The most recent study on lifters (> 6 months of lifting experience) implemented a 16-hour fasting window with a 25% caloric reduction over 4 weeks. Additionally, they ensured protein intake in the range required for hypertrophy (at least 1.8 grams/kg of body weight) and they provided 50 grams of whey protein immediately following each training session. In comparison to a non-time restricted eating, 25% caloric reduction group, there were no significant differences. Both groups saw a reduction in fat mass and maintenance of muscle mass along with improvements in strength. Since these were not experienced lifters the improvements in strength were explained by neurological improvements.
 
The final 2 of the 5 mentioned studies did not use a controlled TRE program, they used participants observing Ramadan. During the month of Ramadan, fasting occurs during the daylight hours so depending on geographical location and whether a morning meal is eaten, fasting length can range from 11 to 22 hours. One of these studies was on bodybuilders and found no difference in body weight or body composition and the other study focused on power athletes and found no negative impact on power output as long as adequate calorie intake and sleep were maintained.
 
Can the results of these limited studies be applied to true strength/power athletes? I say no. The Ramadan studies do not use a control diet, they simply take body and performance measurements while the participant follows whatever their normal Ramadan eating and training pattern is and the other mentioned studies didn’t use true “athletes”, I would call them recreational athletes at best. Furthermore, none of the studies reported real gains in performance or muscle mass which is the end goal of training.
 
Ultimately, there is no scientific evidence to support TRE being used for athletes in active training or competition. During these parts of an athlete's season, the goal is to make performance gains or maintain peak performance. To achieve this goal, adequate nutrition and meal timing are essential and TRE can impact these factors. That being said, there are always outliers and exceptions.
 
Some evidence in humans indicates that TRE may improve body weight, cholesterol markers, blood sugar regulation, and oxidative stress. Just like with IF, these are all great things for regular folks who are overweight and/or have metabolic syndrome. So, for athletes that fall into the above category and feel TRE could be helpful, it could be used during an “off-season” with the help of a nutrition professional. Additionally, since sufficient energy intake is easily achievable with TRE, some athletes who fall into the above category may even be able to use TRE during active training and competition. While there are athletes out there that swear TRE has improved their performance, I do not think it works for everyone, if an athlete is interested in this, experimentation is necessary and I stress the importance of consulting with a nutrition professional. And, just to reiterate, there are many dietary interventions that can be helpful for weight loss and metabolic syndrome based on individual preference.
 
Prioritizing Protein
 
If IF or TRE is used by any strength athlete it is essential to understand the importance of protein intake. We all know protein surplus is needed for muscle hypertrophy but protein intake is even more important when there is caloric restriction. In the presence of slight caloric restriction and resistance training, a higher protein intake minimizes muscle loss, at least 1.8 g/kg body weight per day. Spreading out daily intake of protein may also be better for optimizing hypertrophy versus intaking larger amounts of protein in a smaller number of meals. If an athlete decides to do IF or TRE, adequate protein intake and intake timing are major considerations to dial in with a nutrition professional.
 
So there you have it, TRE is more appropriate for strength athletes than IF but neither IF nor TRE is recommended for an otherwise healthy athlete in an active training or competition block. This is because nutrient/caloric deficiency is a risk and there is no evidence that it contributes to increased performance, at best TRE can maintain performance. IF and TRE may be appropriate during an offseason/deloading phase for athletes that have metabolic syndrome and/or who are overweight and looking to reduce body fat percentage. Just remember, IF and TRE are just 2 of many effective dietary interventions for these goals.