Intermittent fasting is a protocol in which we restrict food intake for a certain period of time. But can intermittent fasting for athletes improve sports performance? In general, we all fast between 7 and 9 hours of sleep at night, but when we talk about intermittent fasting, we are referring to periods longer than 12 hours without food intake. The most common types of intermittent fasting are grouped into two categories:
Most common types of intermittent fasting
Total restriction of daily intake on certain days.
Within this category we can find two protocols: 1:1, where we fast every other day, or 2:1, where every two days of normal eating, a fasting day is performed, repeating this cycle continuously.
Restriction of the time of ingestion in the day.
Days with fasting periods can be alternated with days of normal distribution of intakes or these fasts can be done on a daily basis. Within fasting days, the most popular protocols in this category are 16:8, where the window of intakes comprises 8 hours versus 16 hours of fasting, and 20:4, where the time of intakes is reduced to 4 hours.
Goal of intermittent fasting for athletes
Intermittent fasting is usually approached with two main goals: weight loss and improved health.
Weight loss is a consequence of caloric restriction, as it becomes more difficult to include the necessary calories in a limited window of time. However, a selection of calorie-dense foods could mean remaining in a caloric surplus. Therefore, it can be used as a tool to reach that caloric deficit, but not as a key to it.
Intermittent fasting also aims to improve health mainly by activating the AMPK pathway (obtaining ATP by alternative pathways and autophagy) and the production of catecholamines: The increased secretion of epinephrine and norepinephrine increases lipolysis, releasing fatty acids into the bloodstream to be oxidized and used as a source of energy. It contributes to decreased glucose utilization (related in part to metabolic flexibility) which may aid in muscle glycogen sparing. However, most of the health benefits can be attributed to caloric restriction and not to fasting per se. This is still unclear in the literature, but it points to being a consequence of caloric restriction.
Therefore, intermittent fasting should be considered as one more tool in order to establish a caloric deficit and, above all, taking into account the adherence of each person. There will be subjects who will experience high anxiety due to fasting and will not adapt to it, and, on the contrary, there will be subjects who will find it more comfortable and will not have any problem eliminating certain meals. For all this, it should be a choice of each subject based on his or her personal tastes, since the same objectives can be achieved with or without fasting, if the right nutritional plan is followed.
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Intermittent fasting for athletes
In athletes the scenario is different because every approach to both training and nutrition has one goal: performance. It is important to know how to apply this protocol correctly in athletes so that performance is not affected.
The first thing to keep in mind is that before starting an intermittent fasting protocol, athletes should consider asking for help from a dietician-nutritionist who can guide them and tell them what their specific needs are and how to meet them, as well as how to monitor them. Athlete and nutritionist will decide what type of intermittent fasting may fit in your case, as well as the transition you should take to use the correct protocol.
In the case of deciding to use fasting protocols, it is advisable that the training is done in the hours in which we can eat food or at the end of the fast. For this, we will have to adapt in many cases the sports practice to the protocol of meals. All this, taking into account that there may be double training sessions during the day.
In the case of athletes with a high calorie requirement (endurance or bodybuilding athletes) limiting the total calorie intake to a period of 6-8 hours can generate intestinal problems as a result of overfeeding in such a short time. (1)
Regarding nutrient intake in these athletes, protein will be a macronutrient that should be kept relatively stable at all meals, but different intakes of carbohydrates and fats can be used at each meal in order to prioritize performance or satiety, among others. Depending on the sport modality, it will be important to adjust the amount of carbohydrates and their complexity, as they are the main responsible for optimal performance. Beyond their use as a source of energy, it has been described that the level of glycogen stores plays an important role as a signal conditioning both short-term performance/fatigue and adaptations to training. At the same time, it may be advisable to have a high fat intake in the last meal before starting the fast due to its great satiating effect. And finally, proper hydration should be maintained throughout the day. (2)
It should also be noted that this protocol is especially contraindicated for subjects with eating disorders (ED) and, let us not forget that the vast majority of researchers recognize a higher incidence of ED in the world of sport, especially in female professional athletes, of whom more than 60% experience a disorder of this type throughout their sporting career.
For all these reasons, our general recommendation is not to use an intermittent fasting protocol in athletes who want to improve their performance, especially in cases with several demanding training sessions and in cases of high caloric requirements. Despite the benefits that fasting can bring, an athlete with special requirements will always benefit from having a perientrene supply of carbohydrates and amino acids, in addition to the inconveniences and problems that can arise from limiting food intake to a short period of time or the disruption of circadian cycles when adapting training to meal times.
Its use in athletes who must follow this protocol for religious reasons, such as Muslims during Ramadan, is understandable. But it loses its logic to use it unless the person’s key objective is the loss of body fat.
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- Levy E, Chu T. Intermittent Fasting and Its Effects on Athletic Performance: A Review. Curr Sports Med Rep. 2019 Jul;18(7):266-269. doi: 10.1249/JSR.0000000000000614.
- Correia JM, Santos I, Pezarat-Correia P, Minderico C, Mendonca GV. Effects of Intermittent Fasting on Specific Exercise Performance Outcomes: A Systematic Review Including Meta-Analysis. Nutrients. 2020 May 12;12(5):1390. doi: 10.3390/nu12051390.