L-carnitine is a chemical produced in the human brain, liver and kidneys. It helps the body convert fat into energy. And 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. But it is not clear whether the benefits of these other carnitines are the same. This is also used to increase L-carnitine levels in people whose natural L-carnitine levels are too low. Some people also use L-carnitine for cardiovascular disease, severe kidney disease, and many other conditions, but there is no good scientific evidence to support this use.