The importance of body carbohydrate (CHO) stores in supporting exercise capacity was established a century ago. Since then, sports nutrition guidelines have recommended that endurance athletes optimise their competition performance by implementing dietary strategies that achieve high CHO availability. Periodically, however, this principle has been challenged by the enticing view that the endurance performance could be enhanced by better utilisation of the body’s relatively larger fat stores. For example, during 1985-2005, studies examined the proposal that adaptation to a low-CHO (< 25% energy) high-fat (>60% energy) diet (LCHF) to increase muscle fat utilisation during exercise could enhance performance in trained individuals by reducing reliance on muscle glycogen. As little as 5 days of training with LCHF retools the muscle to enhance fat-burning capacity with robust changes that persist despite acute strategies to restore carbohydrate availability (e.g. glycogen supercompensation, carbohydrate intake during exercise). Furthermore, 2-3 week exposure to minimal carbohydrate (< 20 g/d) intake has been shown to achieve adaptation to high blood ketone concentrations. However, the failure to detect clear performance benefits during endurance/ultra-endurance protocols, combined with evidence of impaired performance of high-intensity exercise via a down-regulation of carbohydrate metabolism led this author to dismiss the use of such fat adaptation strategies by competitive athletes in conventional sports. Recent re-emergence of interest in LCHF diets, coupled with anecdotes of improved performance by sportspeople who follow them, has created a need to re-examine the potential benefits of this eating style. Unfortunately, the absence of compelling data to support this proposal prevents a different conclusion from being made. Notwithstanding the outcomes of future research, there is a need for better awareness of current sports nutrition guidelines which promote an individualised and periodised approach to fuel availability during training, allowing the athlete to prepare for competition performance with metabolic flexibility and optimal utilisation of all muscle substrates. While there may be a few scenarios where LCHF diets are of benefit, or at least are not detrimental, for sports performance, the advantages of CHO as a fuel for the brain and muscle should not be forgotten.