Intermittent fasting

Intermittent fasting for athletes: Does it affect performance?

Over recent years, intermittent fasting (IF) has gained popularity, being promoted by many as a superior diet for weight loss, reducing inflammation, and improving metabolism. Many of these claims are backed by anecdotal evidence and historical practices, however, amongst the recreational and elite athlete population, there is little evidence to support these claims being beneficial to performance. We know training fasted means you are utilizing fat as a source of energy, but this isn’t necessarily leading to loss of body fat. So let’s get to the bottom of this topic, starting with fasting itself.

Intermittent fasting

What is Intermittent Fasting?


Just as the popularity of IF has increased, so has the range of different methods of intermittent fasting. These methods are each aimed at limiting food intake for a certain period of time, to reap the supposed benefits.

One of the many types of time-restricted fasting is the 16/8 method, which involves fasting daily for 16 hours with a restricted 8-hour window to eat. With this method, people typically won’t eat after dinnertime, and their first meal of the day is usually around lunchtime. Another type of fasting which is just as common is whole-day fasting, which includes the 5:2 method. This method involves complete fasting (or consuming no more than 500kcal/day) for 2 days out of the week, which can be consecutive days or split over the week.


The bottom line is that IF is just another way to create a calorie deficit. For the purpose of weight loss, it is important to note that studies show that fasting isn’t any more effective at producing weight loss or weight maintenance than a well calorie-restrictive diet.


Why intermittent fasting isn’t recommended for most athletes


For an athlete, there are several downsides that come with intermittent fasting, including:

  • Compromised performance as a result of training whilst fasted. As training whilst fasted of fuelling carbohydrates impairs performance outcomes.

  • Recovery can be impaired, especially if fasting continues after exercise. This is due to the failure to adequately replenish glycogen stores and promote muscle protein synthesis and repair with post-workout refueling.

  • Concentration and energy levels become depleted during fasting periods, making it difficult to work or perform optimally during this time.

  • Reduced capacity to build muscle mass, as there is less opportunity to spike muscle protein synthesis during times of fasting. The optimal rate of muscle protein synthesis requires 20-30g of protein every 3-4 hours, and this cannot be achieved whilst fasting.

  • There is a risk of overconsumption during the window of time for eating, due to hunger and deprivation. This poses the risk of “undue” the calorie deficit induced by fasting and thus body composition goals may not be achieved as a result.

  • Although the intention of fasting may have been harmless initially, some athletes can go on to form a poor relationship with food as a result.

  • Intermittent fasting is not consistent with current eating cultures, therefore there may be additional stress as a result of intermittent fasting eating patterns and the diet is usually not sustainable for longer periods of time.


You know what else can affect performance – SLEEP! Here is what you need to know about how sleep affects you athletic performance


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