What is L-Carnitine? Carnitine or L-Carnitine is an amino acid found in red meat and dairy. As a nutritional supplement, it can aid weight loss by increasing fat metabolism by converting fatty acids into energy. A simplified explanation of how L-Carnitine works is by carrying fatty acids into the mitochondria of each cell, where they are metabolized for energy. What are the effects of L-Carnitine? The mitochondria of each cell in our body can be considered the “furnaces” of a cell.