EFFECT OF MEDIUM-CHAIN TRIACYLGLYCEROL AND CARBOHYDRATE INGESTION DURING EXERCISE ON SUBSTRATE UTILIZATION AND SUBSEQUENT CYCLING PERFORMANCE

The aim of this study was to investigate the effect of medium-chain tr iacylglycerol (MCT) ingestion during exercise on subsequent time-trial cycling performance. Seven well-trained cyclists performed four exerc ise trials consisting of 2 h at 60% of maximal oxygen uptake followed by a simulated time trial tie, completion of a preset amount of work a s fast as possible) of approximate to 15 min duration. During the tria ls, subjects ingested 1) a 10% carbohydrate solution (CHO; 170 +/- 6 g glucose), 2) a 10% carbohydrate electrolyte with 5% MCT solution (CHO + MCT; 85 +/- 3 g MCT), 3) a 5% MCT solution, or 4) artificially colo red and flavored water (placebo). Neither CHO nor CHO + MCT ingestion had any effect on performance compared with placebo ingestion, whereas ingestion of MCT had a negative effect on performance. Average work r ates during the time trial were 314 +/- 19, 314 +/- 13, and 312 +/- 18 with CHO, CHO + MCT, and placebo, respectively, and was 17-18% lower in the MCT trial (263 +/- 22 W). In addition, compared with placebo in gestion, MCT ingestion had no effect on total rates of fat or carbohyd rate oxidation, nor did it affect exogenous or endogenous carbohydrate utilization. The negative effect of MCT ingestion was associated with increased gastrointestinal complaints tie, intestinal cramping). Thes e data suggest that large amounts of MCTs (85 g) ingested during prolo nged submaximal exercise may provoke gastrointestinal problems leading to decreased exercise performance.