Ketones are organic compounds produced when the body breaks down fats for energy, especially when carbohydrate intake is low. They serve as an alternative fuel source for cells, particularly during periods of fasting, prolonged exercise, or low-carbohydrate diets. The three main types of ketones are acetoacetate, beta-hydroxybutyrate, and acetone. In a state of ketosis, the body shifts from using glucose to using ketones for energy. This metabolic state can be achieved through dietary approaches like the ketogenic diet, which emphasizes high fat and low carbohydrate intake. Ketones can also be measured in the blood, urine, or breath to assess the level of ketosis.