Effect of medium-chain triacylglycerol and carbohydrate ingestion during exercise on substrate utilization and subsequent cycling performance

Abstract

The aim of this study was to investigate the effect of medium-chain triacylglycerol (MCT) ingestion during exercise on subsequent time-trial cycling performance. Seven well-trained cyclists performed four exercise trials consisting of 2 h at 60% of maximal oxygen uptake followed by a simulated time trial (ie, completion of a preset amount of work as fast as possible) of approximately 15 min duration. During the trials, 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 colored 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 rates 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 ingestion, MCT ingestion had no effect on total rates of fat or carbohydrate oxidation, nor did it affect exogenous or endogenous carbohydrate utilization. The negative effect of MCT ingestion was associated with increased gastrointestinal complaints (ie, intestinal cramping). These data suggest that large amounts of MCTs (85 g) ingested during prolonged submaximal exercise may provoke gastrointestinal problems leading to decreased exercise performance.

Attenuated gastric distress but no benefit to performance with adaptation to octanoate-rich esterified oils in well-trained male cyclists

“…The impaired performance in this and several of the previous studies might be largely attributed to the substantial gastrointestinal distress (11,12,22); indeed the present study provides quantitative evidence through the relationship with nausea. Additionally, it has been suggested that MCFAs may not even reach the systemic circulation as MCFAs (36), which would exclude utilization of their potentially beneficial properties in the muscle cells.…”

“…On the other hand, other authors have reported non-statistically clear (Pvalue Ͼ0.05) trends toward performance improvements with CHOϩMCT ingestion. Jeukendrup et al (22) and Vistisen et al (36) observed on average 1% and 1.5% improvements in constant work or constant time tests, respectively, when participants ingested a CHOϩMCT supplement compared with CHO-only. The only group reporting a clear performance benefit as a 2.5% (90%CI: 0.5 to 4.5) enhancement in 40-km time following a 2-h preload was also the only group reporting no gastrointestinal distress (35).…”

“…In contrast, 86 g MCT coingested with CHO has resulted in elevation of serum FFA concentration, reduced reliance on endogenous carbohydrate, and performance enhancement (2.5% decrease in 40-km time-trial time) relative to CHO-only ingestion with no reports of gastrointestinal distress (35). In contrast, Jeukendrup et al (22) and Goedecke et al (11,12) did not observe performance benefits when feeding up to 85 g of MCT coingested with CHO during endurance and ultra-endurance exercise, which was related to the development of moderate-to-severe gastrointestinal distress. Additionally, no clear differences between fat and CHO oxidation with or without MCT ingestion were observed in these later studies.…”

No attenuation of gastric distress or benefit to performance with adaptation to octanoate‐rich esterified oils in female cyclists

“…Jeukendrup et al (1998) and Vistisen et al (2003) observed on average 1% and 1.5% improvements in constant work or constant time tests, respectively, when subjects ingested a CHO+MCT supplement in comparison to CHO-only. The only group reporting a clear performance benefit as a 29 2.5% (90%L: 0.5-4.5) enhancement in 40-km time following a 2-h pre-load was also the only group reporting no gastrointestinal distress (Van Zyl, Lambert et al 1996).…”

“…Conversely, Jeukendrup et al (1998) and Goedecke et al (2005); (1999) did not observe performance benefits when feeding up to 85 g of MCT co-ingested with CHO during endurance and ultra-endurance exercise, which was related to the development of moderate-to-severe gastrointestinal distress. Additionally, no clear differences between fat and CHO oxidation with or without MCT ingestion were observed in these later studies.…”