Does fasting make you faster?

The ins and outs of training on an empty stomach

Traditionally, endurance athletes have focused on high-carbohydrate diets prior to prolonged training sessions or events, termed “carbo-loading”; akin to filling the car fuel tank to the brim before embarking on a long drive. In contrast to this long-held practice, some athletes are completing certain training sessions in a fasted state.

While there are several ways to train in a fasted state, as discussed in this review, the current article will focus on one method that is achieved with minimal thought and effort: overnight fasted training. The name certainly gives the details away: wake up, get ready, and head out for your run or cycle before consuming any caloric foods.

Are these breakfast-skippers onto something? Perhaps.

Endurance training in a fasted state is a hot topic of research and the results hint it might be an effective strategy to induce metabolic adaptations and even boost performance. But is the evidence conclusive? Let’s take a look:

• Fat use: Fat oxidation (fat breakdown) appears to be elevated when training in a fasted state, which may speed up the rate at which you lose fat and therefore aid in weight loss.
• High-effort performances: Sprint performances may be compromised after a 4-week overnight fasted training program, although high-intensity aerobic performances (evaluated with a time-to-exhaustion test at 85% of one’s maximum aerobic capacity) appear to be enhanced.
• Low-intensity performances: Endurance performances for cycling and running appear to be improved after completing a 3-week overnight fasted training program. Another study reported superior improvements in maximal aerobic performances after 4 weeks of training in an overnight fasted state. However, these performance benefits are not reported unanimously, with most studies reporting otherwise.

Despite the equivocal evidence either supporting or negating the performance benefits of overnight fasted training, the practicality is indisputable. Many athletes and working individuals need to train outside the 8 am to 5 pm working hours. The obvious solution? Training in the early hours of the morning. Considering that it wouldn’t be wise to eat right before a run or that most people don’t desire a meal at 5 am, these early morning training sessions occur in a fasted state.

Moral of the story: training in a fasted state may help you lose fat faster, but it isn’t guaranteed to make you run or cycle any faster.

Do what works best for you.

Gabriella Florence | Sports Scientist