Project Summary Poor diet and chronic physical inactivity synergize with aging to induce physical decline and cognitive dysfunction. As a result, there is a current push to test various diet and exercise modalities that can improve metabolic health, preserve cognition, and expand health span. Both various forms of caloric restriction and exercise have been shown to provide benefits for metabolism, cognition, and physical function. One popular notion is that fuel oscillations alternating between carbohydrate and fat utilization are beneficial for long term metabolic and cognitive health. A key corollary is that ketone metabolism, triggered by carbohydrate restriction and fat catabolism, may mediate the observed benefits. Indeed, exploiting ketone body metabolism has garnered recent attention as a tool to improve both peripheral metabolism and treat impaired cognition in aging individuals. Rationale for ketone metabolism in brain health originates from the benefits of ketogenic diets or starvation for seizure disorders. Due to the robust stimulation of adipose tissue lipolysis and increased fat oxidation in the liver, exercise is another trigger for hepatic ketogenesis, raising the question of whether the beneficial relationship between brain health and exercise could at least in part be transduced by ketone metabolism. Currently there are large clinical trials testing if ketogenic diets can mitigate or treat cognitive decline and neurodegenerative conditions associated with aging, however, studies investigating mechanisms of action are lacking. This proposal will fill this void by leveraging novel genetic mouse models and cutting-edge approaches to test the central hypothesis that nutritional and exercise-mediated oscillations of integrated ketone metabolism improve neurometabolic health span. Studying mice with selective loss of either hepatic ketogenesis or neuronal ketone oxidation will allow independent dissection of the mechanistic roles of integrated ketone metabolism in mediating the well-described benefits of intermittent fasting (Aim 1) and exercise (Aim 2), which are both established models that provoke ketosis and ketone utilization by the brain, while also improving metabolic and cognitive phenotypes. The specific roles of ketone metabolism on caloric intake; body composition; whole-body energy homeostasis, glucose metabolism, lipid metabolism, and ketone turnover; cognitive function, including memory and executive function; mitochondrial function in brain; metabolic flux (quantified using stable isotope tracers) in brain; as well as the metabolome and transcriptome of discrete anatomic brain regions will all be quantified. Both male and female mice will be examined in mid-life (12 months of age) after chronic Western diet feeding when differences in health span will emerge via cognition, physical function, and metabolic phenotypes. By defining the independent roles of both hepatic ketogenesis and neuronal ketone body oxidation in heal...