The negative health outcomes of under-fuelling are well known. They may include reproductive dysfunction, poor bone health, or gastrointestinal issues- to name a few (click here to find out more). However, less discussed is the performance outcomes of under-fuelling. The irony of this is that many athletes reduce their food intake with a well-intentioned goal of improving performance, but instead the under-fuelling leaves them underperforming. Read on to find out more.

Under-fuelling may impair performance by interfering with an athlete’s ability to adapt to training. This is demonstrated by a study that examined the performance of a group of swimmers over a 12-week period. The group of swimmers were split into a group that was healthy, and another group that demonstrated symptoms of under-fuelling. This study found that the healthy swimmers improved 400 m swim velocity by 9.8% over the season. On the other hand, the swimmers that were under-fuelling had an 8.2% reduction in performance at the end of the season.  Just like rest is necessary after exercise to improve performance, adequate fuelling is also necessary to experience the performance improvements from training. 

When athletes are under-fuelling, they will not be able to fully replenish their body carbohydrate stores that are used as an energy source during exercise. These carbohydrate stores, known as glycogen, are important for athletes to perform at their best. When glycogen stores become depleted during exercise, this results in fatigue and a drop in performance. Athletes that are under-fuelling will often be exercising with low carbohydrate stores, which may prevent them from performing at their best. Beyond the impact on carbohydrate stores, under-fuelling may impair muscle recovery and can increase the risk of iron deficiency or iron deficiency anemia. This too can negatively impact an athlete’s ability to perform at their best.

Under-fuelling can also impair performance by increasing the chances that an athlete is going to miss out on training and competing due to injury and illness. For instance, in one study, athletes with symptoms of under-fuelling had a 4.5 times greater incidence of bone injuries. In another study, which looked at athletes competing at the 2016 Rio Olympics, under-fuelling was the leading variable associated with illness.  Clearly, if an athlete wants to engage in consistent training and avoid being side-lined due to injury and illness, then adequate fuelling is necessary.

The outcomes of under-fuelling are not only health related, but also include impairments to performance. For all the hard work put into training, don’t let your performance suffer due to under-fuelling. If you want to get the most out of your training, then proper fuelling should be your priority.

Categories: Megan Kuikman

Megan Kuikman

Hello! I’m Megan Kuikman. I’m a Registered Dietitian with specialized training in sports nutrition. My goal is to help athletes and active individuals achieve a healthy attitude towards health, training, and food. I empower athletes to fuel properly for training in order to restore their health and enhance performance. You can get in touch with me at:


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