Intermittent fasting has become increasingly popular and is now gaining popularity among athletes.
The practice consists in depriving oneself of food for more or less long periods. Outside of these periods, you can eat any type of food in the amount you want. There are several types of intermittent fasting, including alternate fasting (every other day), modified fasting (reducing calorie intake on two non-consecutive days a week), and time-restricted eating (for example, fasting from 6 p.m. to 10 a.m.).
How does intermittent fasting affect athletic performance? And what are the benefits, practical considerations and risks involved?
I am a dietitian nutritionist with a doctorate in nutrition from Université Laval, and currently a postdoctoral fellow at the Université du Québec à Chicoutimi (UQAC). This article was written in collaboration with Geneviève Masson, a sports nutritionist who advises high performance athletes at the Canadian Sport Institute Pacific and teaches at Langara College in Vancouver.
Variable effects on sports performance
During physical activity, the body mainly uses stores of carbohydrates, called glycogen, as a source of energy. During fasting, glycogen stores decline rapidly. Thus, in order to meet its energy needs, the body increases its use of lipids (fats).
The practice of intermittent fasting has been associated with reduction of fat mass and maintenance of lean mass in athletes. However, as conflicting results from several studies have shown, these changes do not always improve athletic performance.
Several studies have reported that aerobic capacity, measured by a VO2 max test, remained unchanged after intermittent fasting in elite cyclists And runnersas well as well trained long distance And midway runners. In driven runnersthere was no effect on running time (10 km), level of perceived exertion, or heart rate.
Trained cyclists reported an increase in fatigue and muscle aches during Ramadan, but this may partly be due to dehydration, as fluids are also limited during this time when you cannot consume anything from sunrise to sunset.
When fasting, low stores of glycogen (carbohydrates) can limit the performance of repeated and intense efforts. Active adults reported a decrease in the speed of repeated sprints after fasting 14 hours a day for three consecutive days.
Active students reported a decrease in power and anaerobic capacity after ten days of intermittent fasting as assessed by the Wingate (stationary bike) test, although the study reported increased power in the same group after four weeks.
Men And women who followed a weight training program had similar gains in muscle mass and strength when practicing intermittent fasting compared to a control diet. There was no significant difference in muscle power between active men whether or not they practice intermittent fasting. However, one study reported an increase in muscle strength and endurance in young active adults after eight weeks of strength training combined with intermittent fasting.
Thus, as we can see, the results vary greatly from one study to another and are influenced by several factors, including the type of fast and its duration, the level of the athletes, the type of sport they practice, etc. . In addition, very few studies have been performed in women. Also no control group in most studies means that the effect of intermittent fasting cannot be isolated.
So for the moment, it is not possible to draw any conclusion as to the effectiveness of intermittent fasting on sports performance.
Eat before and after training
Athletes who want to use intermittent fasting should consider several practical issues before getting started. Are their training schedules compatible with this dietary approach? For example, does the amount of time an athlete is allowed to eat allow him or her to consume enough food before exercising or to be able to recover after training?
And, above all, what about the quality of food, given that athletes must consume enough protein recover and maintain lean body mass and limit the negative impact on performance?
Questioning the impacts and reasons for fasting
Intermittent fasting can cause too much of an energy deficiency for athletes with high energy needs to overcome. This could be the case for endurance athletes (running, cycling, cross-country skiing, triathlon, etc.) due to their high training volume. These athletes may end up suffering from Relative Energy Deficit in Sport (RED-S), a syndrome that affects, among other things, hormonal secretion, immunity, sleep and protein synthesis. If the deficit is prolonged, it will have a negative effect on the athlete’s performance.
It is also important to question the motivation for adopting such a strict dietary practice as intermittent fasting. Some people do it for religious reasons like Ramadan. Others are motivated by weight control goals and the hope of achieving an “ideal” body according to socio-cultural norms.
A recent study showed a significant association between intermittent fasting over the past 12 months and behaviors related to eating disorders (overeating, compulsive exercise, vomiting, and laxative use). Although this study cannot determine whether fasting causes disordered eating, or whether disordered eating leads to fasting, it does highlight a risk associated with this practice.
Finally, the potential impact of intermittent fasting on social interactions should also be considered. A fasting schedule may limit participation in social activities involving food. What is the risk of negatively influencing the eating behaviors of other family members, especially children or adolescents who see their parents refrain from eating and skip meals?
Is this a good or a bad idea?
With such contradictory scientific data, it is not possible at this time to comment on the effects of intermittent fasting on sports performance.
More studies are needed before this practice can be recommended, especially for seasoned athletes. Moreover, the potential negative effects on other aspects of health, including dietary habits and social interactions, are not negligible.