Author: Travis Kerr
Intermittent fasting, a common dietary strategy, has gained popularity in the past few years. Many people have implemented this type of diet to assist in trimming fat, without understanding the effects that it can have on strength and endurance performance. There are many ways to implement this type of diet (e.g. 16 hours fasted/8 hours fed, 20 hours fasted/4 hours fed, alternate day 24 hour fasting, etc.), which can lead to differences in results. This is because depending on the type and length of intermittent fast that is chosen, the total daily caloric intake is likely to change.
While many people are familiar with studies that have investigated how intermittent fasting can affect weight loss, diabetes, heart diseases, and cancer, most people are not as familiar with the studies that have been conducted to evaluate the effects on muscular performance and endurance. These aspects play a big part in a workout and can cause problems if not adjusted for properly when developing a new diet and exercise plan. For example, if you change your diet and are now consuming more carbohydrates, which results in more glycogen being stored in your muscles, you will be able to lift with more power and for a longer period of time than what you would if you were eating minimal carbohydrates.
One study evaluated how an intermittent fasting diet of 16 hours fasted/8 hours fed, affected athletic males in terms of their strength, body composition, and other health related factors (4). The study performed by Tatiana Moro and team, sought to determine how this type of diet would affect the overall health of these young adult males. They concluded that this kind of diet is effective in decreasing fat percentage while maintaining lean muscle mass and muscle strength (4). They also noted that testosterone and insulin-like growth factor (IGF-1) levels decreased, which are known for assisting with muscle growth, supporting the fact that there was no muscle growth.
A different study, by Grant Tinsley and his team, evaluated a time-restricting feeding (TRF) diet paired with resistance training 3 days a week on recreationally active, but untrained men versus a control group that only participated in the 3 days of resistance training. The TRF diet allowed participants to consume their daily calories within a 4 hour period, 4 days a week without restrictions on what they could consume. The results of the study showed that there was not any lean muscle mass that was added to those who were in the TRF group, whereas, the group that only conducted the resistance training without dietary restriction gain muscle mass (3). In terms of muscle strength, they found no difference between those who fasted and those who didn’t (3). Overall, it doesn’t seem as though their study was able to conclude much, other than intermittent fasting doesn’t seem to have much of an effect on lean muscle mass.
The study conducted by Anis Chaouachi, investigated how intermittent fasting used during Ramadan affected elite Judo athlete’s performance in different types of exercise. Their overall conclusion is that intermittent fasting during Ramadan didn’t have a large effect on the muscular strength or endurance of trained athletes but did lower their body mass and body fat percentage (2). They also reported an increased feeling of fatigue during the fast (2), which could be due to possible dehydration during the day and decreased sleeping times (1)(2). It is important to note that these findings aren’t consistent with findings from other studies. This could be due to the fact that the study focuses on elite athletes who have trained at such high levels, and their bodies are already extremely efficient and weren’t affected as much by the fast.
In a similar study, Brisswalter’s team looked at Ramadan’s intermittent fasting effects on runners and their endurance. They studied young adult males who lived in France at the time. While there was not a change in body composition, they found a significant decrease in performance for a 5000m race (1). This is likely due to muscles not storing as much energy, depleting stored energy quickly, and not being able to create enough new energy to meet the demands of exercise; therefore, tiring more quickly.
Intermittent fasting can be helpful in losing weight, decreasing body fat percentage, and improving other health factors, because it limits the amount of time you have to eat, which tends to decrease caloric intake. When it comes to muscle performance in strength and endurance training, intermittent fasting decreases the muscles ability to perform at the same level that it did prior to the fast. With this in mind, it may be helpful to decrease the intensity and the weight used in resistance training while on an intermittent fast in order to reduce risk of injury. Though performance may not be at the same level it was it was prior to the fast, the benefits of reducing body fat while maintaining lean muscle mass allow for visible progress to be seen.
- Brisswalter, J., et al. (2011). Effects of Ramadan Intermittent Fasting on Middle-Distance Running Performance in Well-Trained Runners. Clinical Journal of Sport Medicine, 21(5), 422-427.
- Chaouachi, J., et al. (2009). Effect of Ramadan Intermittent Fasting on Aerobic and Anaerobic Performance and Perception of Fatigue in Male Elite Judo Athletes. Journal of Strength and Conditioning Research, 23(9), 2702-2709.
- Tinsley, G. M., et al(2016). Time-restricted feeding in young men performing resistance training: A randomized controlled trial. European Journal of Sport Science, 17(2), 200-207.
- Moro, T., et al. (2016). Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. Journal of Translational Medicine, 14(1), 290.