Beta-hydroxybutyrate (BHB) is a type of ketone body produced during the breakdown of fats in the body. It serves as an alternative energy source when glucose levels are low, such as during fasting or a low-carbohydrate diet. BHB is important for maintaining energy levels in the brain and other tissues when carbohydrates are scarce. BHB is commonly associated with ketogenic diets, which emphasize high fat and low carbohydrate intake to promote fat burning. It can also be measured in the blood to assess the state of ketosis, a metabolic state where the body relies on fat for energy instead of carbohydrates.