L-carnitine is a chemical produced in the human brain, liver, and kidneys. It helps the body convert fat into energy. It is important for heart and brain function, muscle movement, and many other body processes. The body can convert it into other chemicals called acetyl-L-carnitine and propionyl-L-carnitine. However, it is unclear whether the benefits of these other carnitines are the same. It is also used to increase L-carnitine levels in people whose natural levels of L-carnitine are too low. Some people also use L-carnitine for heart disease, serious kidney disease, and many other conditions, but there is no good scientific evidence to support this use.