Intermittent fasting is a protocol in which we restrict food intake for a certain period. In general, we all fast between 7 and 9 hours in the hours of night sleep, but when we talk about intermittent fasting, we refer to periods of more than 12 hours without eating. The most common types of intermittent fasting are grouped into two categories:
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 eating normally, a day of fasting is performed, repeating this cycle continuously.
Restriction of intake period in the day.
Days with periods of fasting can be alternated with days of normal distribution of intakes or these fasts can be done daily. Within the fasting days, the most popular protocols in this category are 16:8, where the intake window comprises 8 hours compared to 16 of fasting, and 20:4, where the intake time is reduced to 4 hours.
Goals of Intermittent fasting for athletes
Intermittent fasting is usually set up with two main goals: weight loss and improving health.
Weight loss is a consequence of caloric restriction, since it becomes more difficult to include the necessary calories in a limited time window. However, a selection of high calorie density foods could mean you are still in a caloric surplus. Therefore, it can be used as a tool to reach that caloric deficit, but not as the key to weight loss.
Intermittent fasting also seeks to improve health mainly through the activation of the AMPK pathway (obtaining ATP through alternative pathways and autophagy) and the production of catecholamines: Increased secretion of epinephrine and norepinephrine increases lipolysis, releasing fatty acids into the bloodstream to be oxidized and used as an energy source. It contributes to decrease the use of glucose (related in part to metabolic flexibility) which could help save muscle glycogen. However, most of the health benefits can be attributed to calorie restriction rather than fasting itself. It is something that is still unclear in the literature, but it points to be a consequence of caloric restriction.
Therefore, intermittent fasting should be considered as one more tool in order to regulate a caloric deficit and, above all, taking into account the experience of each person. Some people will experience high anxiety due to fasting and will not adapt well, and, on the contrary, there will be people who feel more comfortable and it will not be a problem for them to eliminate certain foods. Taking all of this into account, it should be a choice of each person based on preferences, since the same results can be carried out with or without fasting.
Intermittent fasting for athletes
In athletes, the scenario is different since every approach to both training and nutrition has one objective: 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 athletes should consider before starting an intermittent fasting protocol is to ask for help from a dietitian/nutritionist who can guide them and tell them what their specific needs are and how to best meet them, as well as keep track of them. Athletes and nutritionists will decide what type of intermittent fasting might suit them, as well as the transition they should take until finding the correct plan.
In the case of deciding to use fasting protocols, it is recommended that the training be carried out in the hours when we can eat or at the end of the fast. To do this, in many cases we will have to adapt sports practice to the meal schedule, taking into account that there may be double training sessions in the day.
In the case of athletes with a high calorie requirement (athletes of resistance modalities or bodybuilding) limiting the total calorie intake to a period of 6-8 hours can cause intestinal problems as a consequence of overeating in such a short time. (1)
Regarding the intake of nutrients in these athletes, protein will be a macronutrient that must remain relatively stable at all meals, but different intakes of carbohydrates and fats may 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 since they are the main responsible for optimal performance. Beyond its use as a source of energy, it has been described that the level of glycogen stores plays an important role as a signal that conditions both short-term performance/fatigue and training adaptations. At the same time, it might be advisable to eat a high-fat intake at the last meal before starting the fast due to its great satiating effect. And finally, you must maintain proper hydration throughout the day. (two)
It should also be noted that this protocol is especially contraindicated for subjects with eating disorders (ED) and, let’s not forget that the vast majority of researchers recognize a higher incidence of ED in the world of sport, especially in professional female athletes, which more than 60% experience a disorder of this type throughout their sports careers.
For all this, our general recommendation is that an intermittent fasting protocol should not be used 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 constant supply of carbohydrates and amino acids in addition to the drawbacks and problems that can arise from limiting food intake to a short period of time or the disorder of circadian cycles by adapting training to meal times.
Its use in athletes who must perform this protocol for religious reasons, such as Muslims in Ramadan, is understandable. But it is not ideal to use unless the key objective of the person 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.