As metabolic substrates, ketone bodies provide an alternative to glucose in order to pro- long survival during starvation. A low carbohydrate, high fat diet can be used to promote ketogenesis without fasting, but long-term compliance can be difficult. Dietary ketone bod- ies may be an alternative method to induce ketosis, so the aim of the work in this Thesis was to investigate the metabolism of exogenous ketones. In the first experimental Chap- ter, the effects of ketone ester and salt drinks on blood β-hydroxybutyrate (βHB), glucose, lipids, electrolytes and pH were determined in healthy humans at rest. Blood D-βHB levels were higher following ketone ester drinks, but it was found that total βHB levels with ke- tone salts were similar, as over 50% of βHB delivered in the salt was the L-isoform, which was only slowly removed from the blood. Circulating glucose and lipid concentrations fell following both ketone drinks. Blood pH fell following ketone ester consumption, but rose following ketone salt drinks, whilst both compounds raised blood sodium and chloride, and lowered potassium. Work in the second Chapter investigated the repeatability of ketone es- ter metabolism with food, successive drinks or continuous nasogastric (NG) infusion. Peak D-βHB levels were repeatable between- and within- subjects at rest but were lower after a meal, although blood acetoacetate, breath acetone and urine βHB were unaffected by feed- ing. βHB kinetic parameters were not altered by existing hyperketonemia from successive ketone ester drinks and total βHB uptake was identical when isovolumetric amounts of ketone ester were continuously infused through a NG tube. The third Chapter explored side-effects of ketone drinks: ketone ester drinks decreased appetite compared to isocaloric dextrose; which may have been linked to effects of βHB on enteroendocrine cells. Fur- thermore, both ester and salt drinks were found to be unpalatable, and to cause a few, mild gastro-intestinal effects that increased with intake. As exogenous ketones could be a per- formance enhancing supplement in sport, the fourth Chapter used a survey to investigate supplement use by endurance athletes. The results demonstrated widespread supplement use, which was highest at the elite level. In the final Chapter, the effect of glycogen lev- els on the oxidation of βHB was determined in isolated perfused rat hearts. Low cardiac glycogen levels decreased βHB oxidation and levels of the intermediates of glycolysis and the Krebs cycle, whilst increasing muscle amino acid levels, suggesting that low glycogen may have impaired anaplerosis. In conclusion, this work extends current understanding of the novel physiological ketosis that occurs following exogenous ketone consumption.

Cardiovascular disease (CVD) is the leading cause of death in the United States. Age is a primary risk factor for the development of CVD and middle-age is a vulnerable period where risk factors for the disease begin to exceed diagnostic thresholds. Interest has increased for the use of low carbohydrate high fat (LCHF) ketogenic diets due to their reported improvements for cardiometabolic health. Supplementation with exogenous ketone esters (KE) has been shown to increase plasma β-hydroxybutyrate (BHB) and mimic the metabolic effects of LCHF ketogenic diets. Evidence suggests elevated concentrations of plasma BHB may lower blood pressure, improve vascular function, attenuate hyperglycemic responses, and enhance cognitive function. The majority of research has been conducted in preclinical models, and whether exogenous KE supplementation has similar improvements in humans of any ages remains relatively unanswered. To address this we conducted a randomized, placebo controlled, crossover design study in healthy, sedentary, middle to older aged adults who received the exogenous KE (or placebo), and consumed the supplement for 2-weeks (3x/day, 15 minutes prior to each meal; breakfast, lunch, and dinner). Our first hypothesis was to test that KE supplementation would improve vascular function by increasing flow-mediated dilation, reducing arterial stiffness, and lowering blood pressure. Secondly, we hypothesized that KE supplementation would attenuate the glycemic response to an oral glucose tolerance test, improve glycemic variability, and show reductions in postprandial glucose levels. Thirdly, we tested the hypothesis that KE supplementation would improve cognitive performance by showing improvements in processing speed, memory, attention control, and executive functions. In support of our first hypotheses, KE supplementation increased flow-mediated dilation (8.1 ± 1.3 vs. 7.7 ± 1.2%, p = 0.023), but it did not show any difference in arterial stiffness or blood pressure. In contrast to our second hypotheses, following the KE supplementation intervention there were no significant difference from the placebo in terms of glycemic response, variability or mean 2-hour post-meal glucose. In support of our third hypotheses, we found a significant improvement in measures of working memory (7.55 ± 0.93 vs. 7.27 ± 0.29, p = 0.026) and inhibitory control (80 ± 38 vs. 87 ± 32ms, p = 0.035) following the 14-day KE supplementation. More research is needed to elucidate the effects of KE on cardiometabolic health and cognition. / Doctor of Philosophy / Recently there has been an increase in the popularity of low carbohydrate high fat (LCHF) ketogenic diets, with advocates for the diet claiming increased benefits in weight loss and blood glucose control, therefore leading to an increased interest for its use in the treatment for cardiovascular disease, obesity, and diabetes. As more evidence has accumulated much of the impact LCHF ketogenic diets are said to have, has been attributed to a state known as nutritional ketosis, which occurs in response to the restriction of carbohydrates from the diet. Ketone esters (KE) have been shown to effectively elevate ketone bodies (alternative energy produced by the body during times when glucose stores are low) without the need of altering one's own diet, however, this method of inducing ketosis is still lacking evidence for its impact on cardiometabolic health in humans. The purpose of these studies is to determine the effect of having sustained elevations of ketone bodies on our health and cognition in humans. Study 1 included healthy, sedentary middle to older aged adults who consumed a KE for 2-weeks (3x/day, prior to each meal) and a placebo. Following supplementation participants completed test to assess our vascular health and blood sugar control. Study 2 included healthy, sedentary middle to older aged adults who consumed a KE for the same 2-weeks (3x/day, prior to each meal) and a placebo. Participants underwent a series of tests to assess cognitive performance. Overall, after a 2-week supplementation period we found significant improvements in our blood vessel function and with cognitive performance where we saw improvements in working memory, and inhibitory control.