Does intermittent fasting improve your sports performance?

By Tarun Sai LomteReviewed by Lily Ramsey, LLMJan 8 2024

In a recent study published in Nutrients, researchers investigated the effects of intermittent fasting on sports performance.

Various dietary patterns or protocols have emerged in recent years to reduce or amplify physical exercise-derived adaptations to improve performance.

Intermittent fasting is one of these strategies, which has garnered renewed interest due to its health effects and body composition improvement in patients with different conditions. Intermittent fasting has been a popular dietary pattern; notwithstanding its popularity, its impact on sports performance is unclear.

Study: Intermittent Fasting: Does It Affect Sports Performance? A Systematic Review. Image Credit: 4 PM production/Shutterstock.com

The study and findings

The present study examined whether intermittent fasting affects professional athletes' performance. The researchers searched the Web of Science, Scopus, and Medline databases using relevant terms for studies that assessed the effects of intermittent fasting in athletes or people engaging in physical activity.

Studies published in 2013 or later and written in the English and Spanish languages were eligible for inclusion.

Database searches identified 114 articles, 92 of which were retained after de-duplication. After title screening, 58 articles were excluded.

Finally, 25 studies were included in the systematic review. Participants in most studies were athletes. One study did not specify whether participants were athletes, while the remainder indicated that participants were physically active.

Most studies reported time-restricted feeding (TRF) with 16-hour fasting and eight-hour feeding windows. One study analyzed overnight fasting, while others examined fasting during Ramadan.

Besides, two studies evaluated the intake of supplements, such as hydrolyzed whey protein (WPH), whey protein concentrate (WPC), and hydroxy methyl butyrate (HMB). One study investigated the differences between carbohydrate-loaded and protein-loaded fasting.

Studies implemented different tests to evaluate performance. Eight studies examined aerobic performance through the 20-minute cycling test, repeated sprints, 10-km test, and treadmill test (TMT).

Tests for anaerobic performance in six studies included stress tests, interval training, Wingate test, and sub-maximal test.

Muscle strength and power were evaluated in eight studies through endurance and maximal strength tests, average power, and peak power tests.

Fifteen studies examined body composition based on lean mass, fat mass, and anthropometrics. Intermittent fasting metabolically affects the composition of the body. This meant that intermittent fasting positively impacts performance, given that body weight reduction is beneficial.

It could represent an appropriate nutritional approach to reduce body fat and maintain muscle or lean mass. A 2021 study with 14 active female participants observed a significant decline in fat among participants who combined high-intensity training with TRF compared to those on a normal diet and high-intensity training.

Another study with 50 healthy participants reported that fasting and physical activity reduced their body fat percentage and body mass index (BMI).

Notably, the efficacy of intermittent fasting was related to the time of intervention and population. Medium- or long-term fasting was more effective than short-term fasting. Moreover, some studies combined caloric restriction with the follow-up of fasting.

Prior studies have highlighted that no dietary protocol is superior (to others) if the caloric deficit is adequate and the dietary plan is adhered to correctly. Thus, caloric restriction is a critical element for fat mass reduction.

Nevertheless, other studies report a higher dietary adherence in individuals following a nutritional plan with intermittent fasting than those on a diet without restrictions.

A review revealed that fasting regulated body weight, improved insulin sensitivity, and strengthened the immune system. Endogenous clocks in the human body, including the hormone adiponectin, mediate some metabolic processes in the adipose tissue.

Changes in the sleep-wake or feeding-fasting cycle alter adiponectin levels, and TRF effectively increases them.

A study of 34 males on resistance training reported increased adiponectin and reduced leptin levels. Moreover, in another study on cyclists, there was a trend of higher adiponectin in the TRF group than in the normal diet group. Some studies speculate that intermittent fasting activates cellular mechanisms for enhanced immune function.

Conclusions

Taken together, intermittent fasting does not negatively impact sports performance and affects body composition improvement.

Notably, there was a negative effect on performance during Ramadan; however, the case of Ramadan is different as the fasting period varies between 12 and 18 hours depending upon the location and season, and unlike other types of TRF, fasting time and restriction any liquid intake last from sunrise to sunset.

Overall, intermittent fasting could be a suitable strategy for athletes to regulate their fat and lean mass, positively impacting performance.