The power of substrate : an examination of the physiological basis for, and functional impact of, a novel nutritional intervention for sports performance

A novel form of nutritional ketosis has recently emerged, based on the consumption of a ketone ester, that has the potential to impact upon sports performance. Ketone bodies are not normally present in the diet in more than trace amounts and are only produced in significant quantities physiologically during times of extreme energetic stress, but appear to be a highly efficient fuel source. The presence of elevated levels of ketone bodies in the absence of calorie deficit is highly novel and represents a fascinating metabolic state both for the examination of substrate selection during exercise and for the potential to impact sports performance. This PhD programme examined the utility of nutritional ketosis in sport by exploring the evidence base for its impact upon exercise performance and examining the translation of this knowledge into interventions in the field during real world sports performance. Study 1 (Chapter 3) established guidelines for dosing by demonstrating that consuming a meal in close proximity to ketone ester dosing (within 30-minutes (F30) compared to 90-minutes (F90)) resulted in a lowering of the area under the curve for ketone body concentration in the 90-minutes post dose (AUC-BHB(0-90), F90 v F30: 260.7 ± 33.6 mmol/l min v 201.9 ± 33.4 mmol/l min; P<0.05) and that reducing the carbohydrate content of the ketone ester drink (F4:1) resulted in an increased accumulation of circulating ketone bodies (AUC-BHB(0-90), F90 v F4:1: 260.7 ± 33.6 mmol/l min v 311.4 ± 49.3 mmol/l min; P<0.05) . Study 2 (Chapter 4) showed that low-dose ketone ester consumption had no effect on long duration cycle performance (20km TT, KET v CHO: 1731.3 ± 113.0s v 1736.9 ± 114.2s; P=N.S.) in contrast to prior evidence for performance impact at higher doses, suggesting that there may be a threshold of nutritional ketosis required to confer ergogenic benefit. In study 3 (Chapter 5) the hormonal response to repeat sprint cycling performance was characterised with transient increases in both testosterone and the more potent androgen dihydrotestosterone (DHT) occurring in response to sprinting. This served as a backdrop to study 4 (Chapter 6) which examined the impact of nutritional ketosis on sprint performance and showed that ketone ester consumption impaired repeat sprint cycling performance (average sprint power, KET v CHO: 507.3 ± 73.3W v 518.1 ± 72.9W; P<0.01) alongside a dampening of the hormonal response that correlated with the performance deficit (r = 0.538; P = 0.047). Finally study 5 (Chapter 7) explored the translation of these findings into field interventions in sport through a case study series demonstrating that dietary ketone ester consumption is achievable during sports training and competition, leading to sustained nutritional ketosis, but that this comes with a significant side effect profile, poor adherence by athletes (31% withdrew from trialling due to perceived side effects of the drink and 26% withdrew from trialling due to a perceived lack of efficacy) and equivocal effects on performance. This work provides novel insight into the metabolic effects of nutritional ketosis in highly trained athletes whilst also highlighting the importance of taking a wider psycho-physiological perspective when translating experimental findings into application for real world sports performance. When considering the potential utility of ketone ester consumption during exercise there may be a narrow window between efficacy and intolerance and much to be determined regarding the conditions under which nutritional ketosis can impact sports performance.