Monocarboxylates have been implicated in the control of energy homeostasis. Among them, the putative role of ketone bodies produced notably during high-fat diet (HFD) has not been thoroughly explored. In this study, we aimed to determine the impact of a specific rise in cerebral ketone bodies on food intake and energy homeostasis regulation. A carotid infusion of ketone bodies was performed on mice to stimulate sensitive brain areas for 6 or 12 h. At each time point, food intake and different markers of energy homeostasis were analyzed to reveal the consequences of cerebral increase in ketone body level detection. First, an increase in food intake appeared over a 12-h period of brain ketone body perfusion. This stimulated food intake was associated with an increased expression of the hypothalamic neuropeptides NPY and AgRP as well as phosphorylated AMPK and is due to ketone bodies sensed by the brain, as blood ketone body levels did not change at that time. In parallel, gluconeogenesis and insulin sensitivity were transiently altered. Indeed, a dysregulation of glucose production and insulin secretion was observed after 6 h of ketone body perfusion, which reversed to normal at 12 h of perfusion. Altogether, these results suggest that an increase in brain ketone body concentration leads to hyperphagia and a transient perturbation of peripheral metabolic homeostasis. energy homeostasis; monocarboxylate transporters; -hydroxybutyrate; obesity; glucose homeostasis DYSFUNCTION IN BOTH CEREBRAL DETECTION OF NUTRIENTS and integration of circulating signals has been implicated in the pathogenesis of obesity and associated disorders (11). For this reason, numerous studies have explored the possible role of nutrient and endocrine sensing of hypothalamic brain areas and their involvement in energy homeostasis regulation (34). The most studied circulating energy substrate is glucose, which represents a critical nutrient monitored by the brain. As the main energy source for brain cells, glucose also plays an important role in brain energy homeostasis (33). However, evidence showing that the brain can use alternative energy substrates has been provided. For instance, fatty acids and ketone bodies contribute significantly to fulfill brain energy needs under specific conditions (6,13,36). Despite the fact that it has been known for decades that cerebral ketone body utilization increases under particular metabolic conditions (13), central ketone body detection has been poorly studied.Under basal conditions, blood ketone body concentrations are low (Ͻ0.3 mmol/l), and their cerebral utilization is considered to be of little significance. However, ketone body levels are increased under conditions such as fasting, type 1 diabetes, or obesity (13). The brain can use ketone bodies when their blood concentrations reach Ϸ4 mmol/l, a value close to the K m of the monocarboxylate transporter 1 (MCT1) expressed on endothelial cells of cerebral blood vessels for ketone bodies (24,31,44). The brain's ability to use ketone bodies varies from...