HCAR2 and type 2 diabetes mellitus: 3-Hydroxybutyric acid, also named β-hydroxybutyrate and 3-hydroxybutyrate (3HB), is a small ketone body molecule produced endogenously by the body in the liver and was demonstrated to reduce the fasting blood glucose level, improve glucose tolerance, and ameliorate insulin resistance in type 2 diabetic mice through hydroxycarboxylic acid receptor 2 (Zhang et al., 2023).