Intermittent Thoughts on Intermittent Fasting - Myth #3: Intermittent Fasting Hampers Athletic Performance.
|Image 1: Would Usain Bolt be able to compete on an intermittent fast? Or would even the performance of the fastest man in the world suffer? (photo by Erik van Leeuwen)|
Now, the purported weight loss benefits of exercising in a fasted state (in fact, the 10 men in the Trabelsi study commenced their exercise protocols about 12-14h after their last meal) have been discussed over and over, both, in the health and fitness community on the Internet, as well as in the scientific literature and the divide between proponents and opponents of doing (specifically) "cardio"-training (I stick to using the expression "cardio" to designate endurance training, although a "real" cardio regimen would consist of a bunch of high-intensity intervals) in a fasted state, appears to be widening - not closing - with the publication of each new study, review or position stand on this controversial topic. While I will try to dig deeper into the purported biochemical and endocrine mechanisms proponents and opponents on each side of the divide are putting forward in one of the next installments of the Intermittent Thoughts on Intermittent Fasting series, I decided that it would be more prudent to stick to the much less debatable results of a handful of significant studies on the effects of Ramadan fasting on the physical and mental performance in active and/or athletic study populations - after all, I assume you would concur, that it makes little sense to look closer at something of which scientists have conclusively shown that it does not work in practice... wouldn't you?
|Image 2: Dehydration is a problem of Ramadan fasting that won't occur upon "intermittent fasting" regimens as they are suggested in the health and fitness community.|
Much more reliable results come from another very recent study by Amir-Hossein Memari, et al. who investigated the effects of Ramadan fasting on body composition, calorie intake and physical performance in young female taekwondo athletes (15-27 years) who continued on their regular training regimens in the four weeks of religious fasting.
|Figure 1: Weight, BMI, waist to hip ratio (indicator of body fat) and calorie intake in female athletes who continued their regular training regimen during 4 weeks of religious fasting (data calculated based on Memari. 2011)|
|Figure 2: Measures of exercise performance in female athletes 2 weeks before (pre), during and 2 weeks after Ramadan fasting (data based on Memari. 2011)|
Did you know that the symptoms of low cortisol are (in parts) identical to those of high cortisol? Low energy levels, weight and particular fat gain and severe problems to get rid of excess body weight are characteristic of both constantly elevated, as well as constantly low cortisol levels.The profound increase in "balance" after the fasting period, aside, the results of the Memari study leave no doubt that athletes on a non-supplemented intermittent-fasting regimen without tight control of the caloric intake can maintain their performance only via a profound and persistant upregulation of glucocorticoids and catecholamines that is (and the skill-related performance tests show that) not sustainable over an extended period of time. Moreover, in the long term, the combination of constantly elevated cortisol levels and the insufficient calorie intake (for an athlete) trigger all the negative adaptations that are characteristic for what I've previously described as "starvation mode", so that the fat gain (as evidenced by the +5% increase in waist-to-hip ratio) in the two weeks after the "intermittent fasting" period is the athletic counterpart to the "YoYo"-effect on starvation diets.
Evidence that even the Ramadan variation (i.e. no fluids and no supplements) of "intermittent fasting" can work for athletes comes from another 2011 study by Rabindarjeet Singh and colleagues from Malaysia and Singapore (Singh. 2011). While the scientists used "perceived" performance indices from questionnaires, their data is still convincing due to the sheer size and heterogenity of their study population (411 male and 323 female Malaysian Junior-level Muslim athletes avg. age 16.3 ± 2.6 y from various sports).
|Figure 3: Effect of Ramadan fasting on perceived performance in 411 male and 323 female Malaysian Junior Level Muslim athletes (data calculated based on Singh. 2011)|
|Figure 4: Effect of Ramadan fasting on perceived snack, fluid and food intake in 411 male and 323 female Malaysian Junior Level Muslim athletes (data calculated based on Singh. 2011)|
|Figure 5: Perceived effects of 4 weeks of Ramadan fasting on alertness / sleepiness in Malaysian junior-athletes (data adapted from Singh. 2011)|