Examining the Effects of Exogenous Ketones on Exercise Metabolism and Performance in Male Varsity Athletes
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Previous research has shown that administration of exogenous acetoacetate (AcAc), beta-hydroxybutyrate (BHB) and glucose in a perfused rodent heart model can increase cardiac output while reducing oxygen uptake compared with glucose alone. With this apparent improvement in mechanical efficiency induced by AcAc and BHB, there is speculation that they may also enhance exercise performance in athletes. Although AcAc and BHB can be produced endogenously, exogenous BHB supplements have recently become commercially available in the form of ketone mineral salts (KS). Research to date has not found any performance enhancing effects of an acute dose of KS but the effects of more regular KS supplementation on whole body metabolism and exercise performance are unknown. Furthermore, medium-chain triglycerides (MCT) have recently been added to KS supplements, as the administration of KS plus MCT in rodents has been shown to increase blood BHB concentrations compared to KS administration alone. Therefore, the overall purpose of this study was to examine the hypotheses that a twice-daily KS plus MCT supplementation protocol would increase mechanical efficiency and improve exercise performance during a submaximal time to exhaustion (TTE) cycling protocol and a time trial (TT) cycling protocol in male varsity athletes. A single-blinded placebo-controlled crossover design was employed where participants were randomized to either a KS plus MCT supplement (0.3 g BHB/kg, 0.18 g MCT/kg 0.02 g Calcium/kg, 0.02 g Sodium/kg and 0.02 g Potassium/kg) or placebo (0.02 g Calcium/kg, 0.02 g Sodium/kg and 0.02 g Potassium/kg). Each phase of the study lasted 8 days. Seven male varsity athletes (25.6 0.3 years of age, 87.7 3.4 kg and 52.9 3.1 mL/kg/min VO2max) were recruited for this study. Prior to initiating the first phase, participants completed a cycling VO2max test and two familiarization sessions to get accustomed to the TTE and TT cycling tests. On day 1 and 5 of each study phase, participants reported to the laboratory for blood collection to assess whole blood [D-BHB] time course responses. On day 6, participants completed a TTE cycling protocol, consisting of a 5 minute warm-up at 50 Watts, followed by 20 mins at 50% of VO2max. Following this work stage, a constant work load corresponding to 70% of VO2max was maintained until participants reached fatigue. Forty-eight hours later (day 8), participants performed a 10-km cycling TT protocol where participants were instructed to complete the 10-km distance in the fastest time possible. Following the TT test, there was a 2-3 week washout period where no supplements were ingested. After washout, the participants began the supplementation protocol with the opposing supplement and repeated the same experimental protocol as described above. KS plus MCT supplementation increased whole blood D-BHB concentrations above baseline measures 30 mins following supplement ingestion, with concentrations remaining elevated for a minimum of 120 minutes. At rest, whole blood D-BHB concentrations peaked at 0.79 + 0.9 mM 90 minutes following supplement ingestion. As hypothesized, twice-daily supplementation of KS plus MCT increased mechanical efficiency during constant load cycling at 70% VO2max (2.82 0.06 L/min vs. 3.14 0.17 L/min, p<0.05)) and increased time to fatigue during the sub-maximal TTE protocol compared to placebo (33.42 4.6 mins vs. 26.51 4.3 mins, p<0.05). Resting (30 min following supplementation) and exercise measurements of whole blood BHB were significantly elevated in the KS condition, while serum glucose was not different between KS and placebo. Compared with placebo at rest and during constant load cycling at 50% VO2max, serum insulin was significantly elevated (9.58 2.5 mIU/L and 3.21 1.8 mIU/L vs. 6.61 1.7 mIU/L and 1.26 0.4 mIU/L, p<0.05) and plasma glucagon was significantly reduced (33.76 1.69 pg/mL and 124.22 4.93 pg/mL vs 29.27 2.52 pg/mL and 111.94 8.29 pg/mL, p<0.05) in the KS plus MCT condition, suggesting that KS plus MCTs blunted the counter-regulatory response to exercise. However, blood concentrations of cortisol, GH and lactate were not statistically different between conditions at all measurement time points of the TTE. Similar results were found with serum NEFA, although concentrations were significantly higher in the KS plus MCT condition at fatigue (1.87 0.53 mMol/L vs. 1.22 0.16 mMol/L, p<0.05). In contrast to the hypothesis, no differences in performance or mechanical efficiency were found between KS plus MCTs and placebo during the TT cycling protocol. Overall, these results indicate that 6 days of twice-daily supplementation of KS plus MCT may enhance prolonged, sub-maximal exercise performance but not moderate-to-high intensity exercise performance.
Cite this version of the work
Riley Sonnenburg (2018). Examining the Effects of Exogenous Ketones on Exercise Metabolism and Performance in Male Varsity Athletes. UWSpace. http://hdl.handle.net/10012/13356