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

Abstract

We investigated the effects of modifying a normal dietary fatty-acid composition and the ingestion of high-fat exercise supplements on gastrointestinal distress, substrate oxidation, and endurance cycling performance. Five female cyclists completed a randomized triple-crossover comprising a 2-week diet high in octanoate-rich esterified oil (MCFA), or twice, long-chain fatty acids (LCFA). Following the diets, the participants performed 3 h of cycling at 50% peak power followed by ten maximal sprints while ingesting: a carbohydrate (CHO)+MCFA-rich oil emulsion after (a) the 2-week MCFA-rich dietary condition (MC-MC, Intervention), and (b) after one LCFA-rich dietary condition (LC-MC, Placebo), or (c) CHO only following a second LCFA-rich diet (LC-CHO, Control). Ingestion of the CHO+MCFA-rich oil emulsion during 3-h steady-state exercise substantially reduced endogenous-fat oxidation by 88% (90% confidence interval: 59 to 117%) and 74% (40 to 108%) in the MC-MC and LC-MC conditions, respectively, relative to LC-CHO, but there was no effect of MCFA adaptation. Adaptation (MC-MC) also had no clear effect on endogenous CHO (11%; −10 to 33%) or exogenous octanoic-acid oxidation rates (−2%; −20 to 16%), relative to the placebo (LC-MC). Ingestion/oxidation efficiency of octanoic acid was high (0.98), but the CHO+MCFA-rich oil emulsion caused mild to moderate gastrointestinal distress during exercise and there was no attenuating effect of MCFA adaptation evident, nor any clear benefit of the oil emulsion or adaptation to performance. Plasma triacylglycerol concentrations were lower by 17% (23 to −4%) and 15% (20 to −3%; reduction likely) in the LC-MC and MC-MC conditions, respectively, relative to LC-CHO. Total plasma free-fatty acid concentrations were 20% lower (39 to 3%) in the LC-MC condition, relative to LC-CHO. Plasma glycerol concentrations trended lower in the LC-MC and MC-MC conditions, but uncertainty meant these effects were qualified unclear. There was no clear effect of MCFA adaptation on total and 13C-enriched plasma octanoic acid concentrations, nor were there any detectable elongation products (13C-enriched fatty acids >8:0) seen in the plasma in either the MC-MC or LC-MC conditions. In conclusion, despite high efficiency of exogenous-MCFA oxidation, no clear benefit to prolonged endurance performance was observed with the ingestion of a CHO+MCFA-rich esterified oil emulsion or following adaptation to a MCFA-rich diet in female cyclists.