How L-Carnitine should be used and what to take it with. Supplement manufacturers are quick to tell you how wonderful it is but then leave out some critical information, such as L-Carnitine is fairly useless unless you trigger an insulin spike via carbohydrates and/or protein in order to shuttle it into muscle tissue. I introduce one type of Carnitine product and answer the question of why some forms, like acetyl-l-carnitine, are usually found in pills and in smaller doses. What are the advantages of each kind of l-carnitine? And how can you get the most from it?