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)

In the first three installments of the Intermittent Thoughts on Intermittent Fasting series, you've already learned that, just as an increase in meal frequency does not magically strip off unwanted fat-weight, a decrease in meal frequency and thus extended time without "fuel" will not automatically predispose you to obesity. In fact, the deliberate restriction to a narrow "feeding window", which obviously is the main feature of intermittent fasting, and the associated unconscious/voluntary caloric restriction and macro-nutrient modulation have been shown to induce weight loss. This appears to be specifically likely, when - like during Ramadan fasting - the "feast", i.e. the 1-2 gorgeous meals consist of nutritionally (not calorically!) dense whole foods. In the last installment, you've also learned that compared to every-other-day fasting, Ramadan fasting, with its shorter ~15h fasting periods, combined with regular (3x a week) led to a more pronounced and certainly visible -2.6% reduction in body fat in a group of 10 recreationally active study participants (Trabelsi. 2011).

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.

Note: I just want to remind everyone that, although Ramadan fasting with its 15-16h fasting periods may be a better model of the general accepted health and fitness interpretation of "intermittent fasting", the questionable (from a health perspective) water abstinence, as well as the eschewal of BCAAs, protein shakes, stimulants and other supplements "intermittent fasters" are commonly using in their endeavor to "optimize" fat loss, performance and whole body nitrogen balance, are major and potentially important differences, in light of which the overall results of thusly "optimized" intermittent fasting regimens can be expected to surpass (in a beneficial sense) those of religious fasting, especially as far as the maintenance or even improvement of athletic and cognitive performance and the retention of lean mass are concerned.

The first relevant result actually stems from the Ramadan study by Trabelsi, et al. (Trabelsi. 2011). Obviously, the subjects in his study did not feel like their empty stomachs would compromise their exercise performance. Now, though the "rate of perceived exertion" may be a frequent measure in scientific studies into the effects of specific training regimens, supplements and/or combinations of both, it is not the most reliable measure and I assume that most of you know that - especially when it comes to recreational activities like the ones Trabelsi's study participants performed - the way we feel during and after a given exercise is a notoriously unrealiable measure of "performance".

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)

From the data in figure 1 it becomes immediately obvious that, contrary to the recreationally active subjects in the Trabelsi study, who obviously were free to adapt intensity, duration and type of their 3x/week athletic activity according to their fasting regimen, the body composition of the female athletes was not beneficially influenced by the "intermittent fast". On the contrary, despite (or I suspect rather due to) a pretty harsh reduction in caloric intake (absolute values -500kcal from 1658kcal/day to 1163kcal/day) over the four weeks of fasting, the ladies lost only 1.63kg of weight. In view of the fact that their waist to hip ratio increased even before the compensatory overeating in the two weeks after Ramadan (post), it stands to reason that most of the "weight loss" was in fact water-weight (remember the ladies didn't drink before sundown), so that I would venture the guess that their body-fat percentage, which unfortunately has not been measured by the scientists, will have increased during the fast, as well.

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)

Contrary to what you may have expected the athletes were yet able to maintain, in the first two weeks of fasting even improve their performance in agility, balance and vertical jumping tests (cf. figure 2). Given the fact, that even in the first two weeks of Ramadan, the women had reduced their already surprisingly low caloric intake (1658kcal/day) by -16%, certainly is a surprising result. If, however you remember my elaborations on the cortisol and catecholamine response to fasting from the first installment of this series and, at least for the moment, do away with the unreasonable vilification of temporary increases in cortisol that is so rampant in the bro-scientific world of bodybuilding and fitness forums, you may realize that the performance increase you are getting from your favorite stimulant or pre-workout product is the immediate result of its high caffeine, geranamine or whatever other methyl-xanthine content's ability to trigger a profound stress response. Now, the longer-term trade-offs of these short term benefits are the well-established induction of insulin-resistance, the down-regulation of the endocrine system (thyroid and sex hormone production) and the ensuing decrease in energy expenditure that are falsely ascribed to cortisol in general.

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 3 cleary shows that, despite the fact that the number of junior-athletes who felt that fasting had a negative effect on their performance is greater, than the number of athletes who felt they would benefit from fasting, the vast majority of athletes, i.e. more than 70%, either felt no effect or were not sure - regardless of whether they participated in team, skill-based, endurance or combat sports. In that, I think it is noteworthy, that in athletes who participate in endurance sports, the number of athletes who experienced negative effects of fasting outnumbers those who felt benefits by factor x7. In combat sports (listen up weight-lifters), on the other hand, the number of athletes who consider fasting beneficial is almost identical to the number of athletes who felt that their performance decreased over the course of four weeks.

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)

General variations in athletic and thus caloric and nutritional demands, aside, the obvious differences to the Memari study may well be explained by superior or maybe just less restrictive feeding practices in the younger athletes, the majority of whom, as the data in figure 4 goes to show, managed (and were psychologically able / I am referring here to the fear of getting fat that is unfortunately pretty prominent among post-pubertal female athletes esp. if weight classes are an issue as in the taekwando athletes from the Memari study) to compensate for the lack of snacks, fluid and overall caloric intake in the fasting periods by "feasting" after sundown.

Figure 5: Perceived effects of 4 weeks of Ramadan fasting on alertness / sleepiness in Malaysian junior-athletes (data adapted from Singh. 2011)

Despite the absence of negative effects on exercise performance in the majority of the study participants, more than 66% of the young athletes felt sleepy and less alert in the course of the day and roughly 50% of them felt that their sleep quality or the duration of their sleep were affected by their fast. How all that ties back into the profound endocrine changes that are induced by modulating food and macronutrient intake and frequency (you can read up on closely related and probably even more surprising beneficial effects of eating all your carbohydrates after 6pm in a previous blogpost of mine), along with tips how to counter detrimental effects by meal-timing, macronutrient selection and supplements will be the topic of the next installments of the Intermittent Thoughts on Intermittent Fasting series, which - due to my tight time-schedule - won't be written before the coming weekend. For the time being, I want to remind you that comments, critique, suggestions and questions are always welcome and may be posted via Facebook, Twitter or in the comments area of this page.