By Kelly Schreuder – Registered Dietician & Private Chef

Carbohydrates and fats are both generally considered excellent fuel sources in our diets. A well-adapted body can use these substrates interchangeably, depending on the intensity of the exercise. In general, at higher intensity, carbohydrate is a preferable fuel source, simply because in theory fat takes longer to convert into usable energy than carbohydrate. We also know that in healthy individuals, following a lower carbohydrate diet leads us to metabolise more fat as a substrate at rest, and it seems to be possible to train our bodies to use more fat as fuel over time.

Up until recently, the research around fats versus carbohydrates in exercise showed very little obvious performance benefit to athletes in using more fats. There is also a general health concern that a very high fat and low carbohydrate diet has the potential to be overly restricted in terms of nutrients that are available in a variety of carbohydrate-containing foods. For reasons like these, research around lower carbohydrate diets and fat adaptation for athletes seemed almost unnecessary.

More recent research is showing us that athletes following a lower carbohydrate diet generally are able to perform at least as well as those following a mixed diet. There is also currently plenty of public interest in low carbohydrate diets for weight loss, and there many enthusiastic anecdotal claims and individual success stories from athletes following high fat diets in the media. However, the advantage of following a low carbohydrate diet exclusively for all athletes is less clear and there is not enough available research to create blanket recommendations around quantities. Further, there is the real possibility of reduced performance at high intensities if there is not enough available carbohydrate. Another aspect to consider is that carbohydrates can help us to absorb fluid. For an athlete, that alone may play a fairly important role in performance.

There may be some benefit of a low carbohydrate diet to those trying to lose weight, or those who have certain digestive concerns – like irritable bowel syndrome – where avoidance of some carbohydrate foods is associated with health improvements. A slightly overweight amateur cyclist, for example, who goes out for a couple of hours on a fairly low intensity ride might do very well to limit carbohydrate intake during training. However, there are no clear disadvantages (and some strong advantages) of carbohydrates to a normal-weight, healthy athlete, racing at high intensity. Having the ability to tap into fat generally as an additional fuel source seems like a good plan – what could be wrong with that? It means you can eat a variety of food and macronutrients, and still function well, and for some athletes that means fat adaptation during training can be beneficial.

The key issue is that the research is not yet sufficient to give general advice around fat adaptation. Sports nutrition is an individual game. What may work for one individual could be totally ineffective for another. Even the established theory around carbohydrates is nothing without some really good trial and error. You can reduce the trial and error of sports nutrition somewhat by seeing a nutrition professional for individual planning and guidance that considers all the issues, or by having metabolic testing to determine your levels of substrate use. One thing that is always a good idea is to have a back-up plan if you are trying anything experimental when you train, especially if you are going to be far from home. By all means, try training on a lower carbohydrate diet if that feels right to you, but take an extra carbohydrate snack in your back pocket in case it doesn’t feel great.