STRATEGIES TO ENHANCE FAT UTILIZATION DURING EXERCISE

Compared with the limited capacity of the human body to store carbohyd rate (CHO), endogenous fat depots are large and represent a vast sourc e of fuel for exercise. However, fatty acid (FA) oxidation is limited, especially during intense exercise, and CHO remains the major fuel fo r oxidative metabolism. In the search for strategies to improve athlet ic performance, recent interest has focused on several nutritional pro cedures which may theoretically promote FA oxidation, attenuate the ra te of muscle glycogen depletion and improve exercise capacity. In some individuals the ingestion of caffeine improves endurance capacity, bu t L-carnitine supplementation has no effect on either rates of FA oxid ation, muscle glycogen utilisation or performance. Likewise, the inges tion of small amounts of medium-chain triglyceride (MCT) has no major effect on either fat metabolism or exercise performance. On the other hand, in endurance-trained individuals, substrate utilisation during s ubmaximal [60% of peak oxygen uptake ((V) over dot O-2peak)] exercise can be altered substantially by the ingestion of a high fat (60 to 70% of energy intake), low CHO (15 to 20% of energy intake) diet for 7 to 10 days. Adaptation to such a diet, however, does not appear Co alter the rate of working muscle glycogen utilisation during prolonged, mod erate intensity exercise, nor consistently improve performance. At pre sent, there is insufficient scientific evidence to recommend that athl etes either ingest fat, in the form of MCTs, during exercise, or 'fat- adapt' in the weeks prior to a major endurance event to improve athlet ic performance.