A recent editorial by Tim Noakes in the British Journal of Sports Medicine reviews some of the current evidence for low-carbohydrate diets and athletes.
“Once they deplete their endogenous carbohydrate reserves, athletes chronically adapted to high-carbohydrate diets likely become entirely dependent on exogenous carbohydrate for their performance. In contrast, athletes adapted to a low-carbohydrate diet carry all the energy they need in their abundant fat reserves. And because they live and train with chronically low blood insulin concentrations, they have instantaneous access to those fat reserves at all times. Just as should occur in a metabolism crafted by our evolutionary history as predatory hunters.”
“Thus a fully fat-adapted athlete able to oxidise fat at 1.5 g/min would cover his or her energy cost during an Ironman Triathlon without needing to ingest exogenous fuels especially carbohydrate. This contrasts with the need of carbohydrate-adapted athletes to ingest 90–105 g/h during prolonged exercise if they wish to maintain their performance.”
—Br J Sports Med. 2014 Jul;48(14):1077-8.