Push-pull: two distinct strategies to supply the brain with energy substrates. Glucose is the brain’s main fuel and is taken up by the brain in relation to demand. Hence, this is a “pull” strategy because glucose is pulled into the cell following neuronal activation and the subsequent decrease in neuronal glucose concentrations. Ketones are the brain’s main alternate fuel to glucose and are taken up by the brain in relation to their presence in blood. Hence, this is a “push” strategy because ketones are pushed into the brain in direct proportion to their concentrations in the blood.