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

1 Institute of Food, Nutrition, and Human Health, Massey University, Wellington, and 2 Palmerston North, New Zealand; 3 The Copenhagen Muscle Research Centre, Department of Human Physiology, 4 Institute of Exercise and Sport Sciences, Department of Medical Physiology, Panum Institute, University of Copenhagen, Copenhagen, Denmark; 5 School of Sport and Exercise Sciences, University of Birmingham, Birmingham, United Kingdom; 6 BioCentrum-DTU, The Technical University of Denmark, Lyngby, Denmark Submitted 3 April 2006 ; accepted in final form 6 July 2006 We investigated the effects of modifying a normal dietary fatty acid composition and ingestion of high-fat exercise supplements on gastrointestinal distress, substrate oxidation, and endurance cycling performance. Nine well-trained male cyclists completed a randomized triple-crossover comprising a 2-wk diet high in octanoate-rich esterified oil (MCFA) or twice long-chain fatty acids (LCFA). Following the diets, participants performed 3-h of cycling at 50% of peak power followed by 10 maximal sprints while ingesting either 1 ) a carbohydrate (CHO)+MCFA-rich oil emulsion after the 2-wk MCFA-rich dietary condition (MC-MC, Intervention) and 2 ) after one of the LCFA-rich dietary conditions (LC-MC, Placebo) or 3 ) CHO only following a LCFA-rich diet (LC-CHO, Control). During the 3-h ride MCFA-adaptation decreased octanoic-acid oxidation by 24% (90% confidence interval: 14–34%). The CHO+MCFA-rich oil emulsion reduced endogenous fat oxidation by 61% (33–89%) and 110% (89–131%) in the MC-MC and LC-MC conditions, respectively, and MCFA-adaptation reduced endogenous-carbohydrate oxidation by 10% (–3–23%). MCFA-adaptation attenuated gastrointestinal distress and nausea during the sprints, but the effect of the oil emulsion was to lower sprint power by 10.9% (7.7–14.1%) in the LC-MC condition and by 7.1% (5.7–8.5%) in the MC-MC condition, relative to the LC-CHO control; every one unit increase in nausea decreased mean power by 6.0 W (3.2–8.8 W). We conclude that despite some attenuation of endogenous-carbohydrate oxidation and gastric distress following adaptation to a MCFA-rich diet, repeat sprint performance was substantially impaired in response to the ingestion of a CHO+MCFA-rich oil emulsion. medium-chain fatty acids; structured triacylglycerols; dietary adaptation; supplementation Address for reprint requests and other correspondence: D. Rowlands, Institute of Food, Nutrition, and Human Health, Massey Univ., PO Bo