Relative energy deficiency in sport

• Intermittent fasting has become increasingly popular and is now gaining a following among athletes.
• Outside these periods, you can eat any type of food in any quantity you want.
• There are several types of intermittent fasting, including alternative fasting (every other day), modified fasting (reduced calorie intake on two non-consecutive days per week) and time-limited eating (for example, fasting from 6 p.m. to 10 a.m.).
• How does intermittent fasting affect athletic performance?

Varying effects on athletic performance

• So in order to meet its energy needs, the body increases its use of lipids (fats).
• The practice of intermittent fasting has been associated with a decrease in fat mass and maintenance of lean mass in athletes.
• However, as contradictory results of several studies have shown, these changes do not always improve athletic performance.

Power sports

• Active adults reported a decreased speed in repeated sprints after fasting 14 hours per day for three consecutive days.
• Active students reported decreased power and anaerobic capacity after ten days of intermittent fasting as assessed by the Wingate (stationary bike) test, although the study reported that power increased in the same group after four weeks.

Strength training

• Men and women who followed a strength training program had similar gains in muscle mass and strength when practising intermittent fasting compared to a control diet.
• There was no significant difference in muscle power between active men who did or did not practise intermittent fasting.
• However, one study reported an increase in strength and muscular endurance in active young adults after eight weeks of strength training combined with intermittent fasting.

Eating before and after training

• Are their training schedules compatible with this dietary approach?
• For example, does the period during which an athlete is allowed to eat allow them to consume enough food prior to doing physical exercise, or to be able to recover after the training?

Questioning the impacts of — and reasons for — fasting

• Intermittent fasting may result in an energy deficiency that is too great for athletes with high energy needs to overcome.
• It is also important to question the motivation for adopting a dietary practice as strict as intermittent fasting.
• Although this study does not determine whether fasting causes eating disorders, or eating disorders lead to fasting, it does highlight an associated risk in this practice.

Is this a good or bad idea?

• Further studies are needed before this practice can be recommended, especially for seasoned athletes.
• Furthermore, the potential negative effects on other aspects of health, including eating habits and social interactions, are not negligible.