Nutrition Carbs and Sport Performance – Should You Go Low-Carb?


There is a lot of conflicting information around the subject of nutrition and more specifically, around carbs and sports performance. Everyone seems to be doing something different, from keto to low-carb, to training low and competing high, and so on…

But do these strategies actually work?

It can be difficult to navigate information and even harder to know where to find anything reliable. If you can relate, keep reading to find out the evidence.


Carbohydrates (Carbs) are your body’s preferred energy source. You can find them in various forms; starchy foods such as bread, pasta, rice, grains, and cereals and in simple sugars such as refined sugar, honey, syrup, and the like. You can also find them in fruits, vegetables, beans, and dairy products.

All carbohydrates are essentially broken down into sugar molecules in the body and the storage of this sugar is called glycogen. The majority of the body’s glycogen is stored in the muscles and liver. When you exercise, especially at high intensity, your body prefers to use glycogen as its primary energy source.

Your body likes to use multiple sources of energy though. So, instead of only using glycogen, it often also uses fat as a secondary source.

So, should I “go low”?

How you train and how you fuel around your training sessions can directly impact your level of fitness and sports performance.

Traditional approaches to managing nutrition for endurance training have advised to follow a high-carbohydrate diet. New research has emerged in recent years, discovering more about the complexities of fuel and performance. It showed convincing results regarding the possible benefits that a varying intake of nutrients can offer in training adaptations.

Strategies that train our muscles to use fat as the primary energy source over glycogen, essentially make an athlete more efficient at using fat as an energy source over carbohydrates whilst exercising.

Various low-carb diets have been studied. Some include the keto diet, train low and compete high, sleep low, training fasted, and so on. There have been some positive outcomes in muscle adaptions for some of these diets.

Prof. John Hawley and colleagues found that sleeping low may exaggerate some training adaptions. However, results are not consistent.

The concept of “train low and compete high” is to get the best of both worlds, by deliberately reducing carbohydrate availability during training. Then, restoring carbohydrate availability prior to an event so that the athlete can perform at a greater intensity for longer.

While ‘Training low’ can be useful depending on your goals, consistently being ‘low-carb’ is likely to impede your ability to use carbs as a fuel source.

By competition day, this could hinder you more than it helps. Over 70% of the research in this area has produced positive outcomes in muscle adaptations. However, this does not always relate to improved exercise performance.

For studies measuring performance outcomes, only 37% showed improvement, whilst 63% resulted in no change to performance. On the whole, the quality of research is lacking… Therefore we are unable to make appropriate recommendations towards the optimal use of low-carb, high-fat diets for athletic performance.

On the contrary, research consistently shows that exercise with high carbohydrate availability improves acute exercise performance when compared to exercising in a state of low carbohydrate availability.

The evidence continues to highlight the benefits of consuming carbohydrate-rich foods before, during, and after intense training or competitions to ensure that muscle glycogen stores are replenished.

Supporting that ingesting adequate carbohydrates optimizes sports performance and recovery.

Individuals engaging in general fitness and not training for any particular sports performance goal can typically meet daily carbohydrate needs by consuming a “normal” diet. However, athletes involved in moderate or high-volume training need larger amounts of carbs (and protein) in their diet to support the increased demands.

Depending on your goals, you may still want to limit carbohydrates. Therefore, it might be suitable for you to adopt some carbohydrate periodization strategies as part of your nutrition plan. This is to ensure you are adequately fuelled for your hard training sessions and events to optimize your sports performance and recovery.

If you have questions about your carbohydrate intake and fuelling optimally for sports, drop into UFIT to consult a Registered Dietitian or Nutritionist with experience in sports nutrition.


Kerksick, C.M., Wilborn, C.D., Roberts, M.D. et al. (2018) ISSN exercise & sports nutrition review update: research & recommendations. J Int Soc Sports Nutr 15, 38.

Tiller, N.B., Roberts, J.D., Beasley, L. et al. (2019) International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing. J Int Soc Sports Nutr 16, 50.

Jeukendrup, A. E. (2017) Periodized nutrition for athletes. Sports Med, 47 (Suppl 1): S51-S63.

Burke, L., & Hawley, J. (2015) Nutritional strategies to enhance fat oxidation during aerobic exercise. In Burke, L. & Deakin, V. (5th Eds), Clinical sports nutrition (pp 463 – 492). Sydney, NSW: McGraw-Hill.

UFIT Coaching

Comments are closed