Avoiding carbohydrates may compromise exercise training


More and more people are following high fat, low carbohydrate diets in order to lose weight. The idea behind these diets is that the absence of dietary carbohydrate means that the body is forced to utilise fat as its primary energy source. Whilst very low intakes of carbohydrate may lead to short-term improvements in body composition, how would these diets affect endurance athletes who heavily rely on carbohydrate to fuel training and competition?

Research overview

Eight male off-road cyclists to part in a recent study involving the consumption of a high fat, low carbohydrate diet or a more balanced carbohydrate-fat ‘mixed’ diet for 4 weeks.

When on a high fat, low carbohydrate diet, but not a mixed diet, the cyclists experienced reductions in body mass and fat mass. However, high intensity exercise performance was compromised after a high fat, low carbohydrate diet in comparison to a mixed diet.

Take home message

Those involved in endurance sports may consider a high fat, very low carbohydrate diet during select periods of low intensity training where body composition improvements are a priority. However, this type of diet should be avoided for the majority of the training season, as low carbohydrate availability is associated with a decline in performance in high intensity training sessions.

For health reasons those trialing high fat, very low carbohydrate diets should prioritise the intake of foods rich in unsaturated fats (MUFA and PUFA) over foods containing high amounts of saturated and/or trans-fats.


The effects of a ketogenic diet on exercise metabolism and physical performance in off-road cyclists