Success in elite endurance events is underpinned by the athlete’s ability to produce muscular power rapidly and economically throughout the event or at critical moments. The importance of body carbohydrate (CHO) stores as a key muscle substate was established a century ago and formed the basis of the first expert sports nutrition guidelines in the 1990s. The evolution of these guidelines has involved several landmarks and different roles for CHO in the athlete’s training and performance nutrition plans.  An initial change involved an understanding of “CHO availability” – a dynamic evaluation of body CHO stores in relation to the fuel requirements of each training session – rather than total dietary CHO intake per se.  This concept explains differences in the CHO intake of individual athletes, and changes within the same athlete across different days and phases of their training program according to the fuel needs of each session.  Contemporary sports nutrition guidelines for competition performance promote a range of strategies before, during and between events to ensure that endogenous and exogenous sources of muscle CHO meet the fuel needs of the event.  Optimal strategies for CHO loading and CHO intake during the event have evolved in terms of the timing, amount and source of CHO involved in the plan.  Advances in the molecular approach to exercise provided insight that deliberate manipulation of low CHO availability during and in the recovery from an exercise session may upregulate cellular signalling and increase the adaptive response to endurance exercise.  Although there is evidence of cellular benefits with a possible transfer to performance advantages in sub-elite athletes, the integration of “train low” strategies in the diets of elite athletes may be less effective.  A separate strategy which involves chronic implementation of a low CHO diet aims to retool the endurance-trained muscle to dramatically increase its capacity for fat oxidation as a replacement for its reliance on the finite body CHO stores. Despite popular interest and hype, adaptation to ketogenic and non-ketogenic versions of low CHO high fat diets has between shown to impair rather than enhance performance of elite endurance athletes, potentially due to the lower economy (higher oxygen cost) of fat oxidation compared with CHO oxidation, and the impaired utilisation of CHO stores that may be reintroduced.  A final thread involves the recognition of the central benefits of CHO availability, particularly the benefits of mouth-sensing CHO to activate reward and pacing centres in the brain.  This may be implemented in terms of timing of intake of CHO during competitive events as well as the use of CHO mouth rinses during fatiguing “train low” training sessions.