A ketone is a type of organic compound characterized by a carbonyl group (C=O) bonded to two other carbon atoms. Ketones are commonly found in various substances, including some sugars and fatty acids. They play a significant role in metabolism, especially during periods of low carbohydrate intake, when the body breaks down fats for energy. In the human body, ketones are produced in the liver from fatty acids during a process called ketosis. This typically occurs when carbohydrate intake is low, such as in ketogenic diets. Ketones can serve as an alternative energy source for cells, particularly for the brain, which usually relies on glucose.