Ketosis is the metabolic state defined by the increase in ketone bodies. It is generally accepted that one is in ketosis when blood levels of the primary ketone body, beta-hydroxybutyrate (BHB), exceed 0.5 mmol/L. With the exception of ketosis induced by exogenous ketone supplements, this metabolic switch occurs in low glucose and therefore low insulin states. When we stop eating carbohydrates or start fasting, the body burns its available glucose stores, insulin levels drop, the glucose (glycogen) stored in our liver is depleted, and the body slowly enters a state fat burning. The brain cannot rely on fat for fuel, but needs an alternate energy source in the absence of glucose, so the liver turns fat into ketones instead. These ketones enter the bloodstream and are delivered to our tissues for fuel.