Intermittent fasting and sports - is this possible?

Joëlle Flück 3. March 2020

Intermittent fasting is bang on trend. What is it? Who is it suitable for? Is it compatible with sports? Here are the most important answers.

Presented by Swiss Sports Nutrition Society

Intermittent fasting means abstaining from eating for various periods of time, for example, on a daily or hourly basis. The goal is usually to lose weight in the long term. There are various well-known forms of intermittent fasting such as «Dinner Cancelling», for example, where you skip the evening meal. Other forms involve fasting only every second day and then eating normally again or 16:8, which is the best-known form where you eat over an 8-hour period and fast for the remaining 16 hours.

Intermittent fasting is basically said to have a sustainable health-promoting effect. For example, «Dinner Cancelling» is supposed to promote healthy weight loss and improve the quality of sleep. This form of fasting is also supposed to improve insulin levels. Animal studies have shown that intermittent fasting reduces the risk of cardiovascular diseases (e.g. diabetes). Unfortunately, there are very few studies that have investigated this in humans and the assertions are relatively inconclusive. However, the existing studies indicate that intermittent fasting with regard to weight loss, lean mass and fat mass as well as glucose metabolism can be a good alternative to conventional fasting methods. In sports, this would be a sensible way to lose weight and still retain muscle mass. However, you need to pay attention to which nutrients you consume and how large the portions are in the «non-fasting period». If you don’t make sure you eat a healthy and balanced diet, or consume too much energy, this can effectively curb weight loss or even prevent it altogether. This fasting method also has some disadvantages in terms of athletic performance.


If, as an athlete, you use «Dinner Cancelling» as a fasting method, for example, and also train in the late afternoon or early evening, your ability to regenerate will be clearly restricted. Your body would not receive the necessary carbohydrates and proteins after this unit, thus increasing your susceptibility to infection. Should you want to use this method, it would make more sense to complete your training unit in the morning to ensure your body is supplied with important nutrients again afterwards. This is particularly crucial for strength athletes, since strength training is optimised by the intake of protein, which promotes muscle protein synthesis.

It gets more difficult when you don’t eat anything on certain days. On these days, the supply of nutrients is too low or completely lacking. It is probably worthwhile moving your training units to the days on which you are eating again. Otherwise you run the risk of neither having an optimal energy supply nor recovery capability and will increase the risk of injuries or infections. What’s more, during tough training phases this can even lead to over-training. In any case, it is worth carefully considering to what purpose and in which phase such a fasting method should be used, if at all. Ideally, you should fast when you are not doing any training to ensure your performance and recovery capability are not restricted. Should you still decide to use such a fasting method during a training phase, it is worthwhile not to train too intensively or extensively, since the body receives too few important nutrients during this time and is generally in a negative energy balance. If this negative energy balance lasts too long (e.g. several weeks) or is too big, as already mentioned, the risk of infection and injury increases, and the quality of training is reduced. In this case, individual planning and coordinating your training, nutrition and recovery is worthwhile so as not to jeopardise your health in the long term.


Fasting is never an optimal strategy for improving the performance of athletes. However, if the goal is weight loss, then this method could well be effective. Nevertheless, the optimal timing of such an intervention and the coordination of training, recovery and nutrition are extremely important. It is highly feasible for recreational athletes completing 3 units a week. It becomes much more difficult when completing one or even more units each day. If need be, weight loss can be induced through other dietary adjustments without restricting your athletic performance or recovery capability, and without having to skip entire meals. It is therefore worthwhile discussing the timing and possible measures for weight loss with a sports nutrition specialist.