What is Doctor's Best L-Carnitine Fumarate? Doctor's Best L-Carnitine Fumarate helps the body burn fat for energy and helps maintain a healthy heart and cardiovascular system. L-Carnitine is a nutrient that promotes energy production in cells by transporting fatty acids into the mitochondrion, an intracellular structure that generates metabolic energy in the form of ATP. In this role, L-carnitine helps the body efficiently metabolize fat. Fumarate is a naturally occurring compound in the body. Fumarate serves as an intermediate in the Krebs cycle, a key energy-producing process that takes place in the mitochondrion. Doctor's Best Carnitine Fumarate is derived from pharmaceutical grade L-carnitine manufactured by a patented, FDA-approved process. How does it work? L-carnitine promotes energy production in cells by transporting fatty acids into the mitochondrion. Its primary function is to transfer long-chain fatty acids across the inner mitochondrial membrane. Fatty acid molecules are activated to coenzyme A (CoA) esters in the cytoplasm of the cell, and then esterified to L-carnitine. The combination of a fatty acid molecule and L-carnitine is called "acyl-carnitine." Much of the body L-carnitine content is stored in the form of acyl-carnitine. The mitochondrion is the cell's energy-generating furnace. Called an "organelle," the mitochondrion is a self-contained structure inside the cell. Like all cellular structures, the mitochondrion is surrounded by a membrane. This membrane is an impenetrable barrier to acyl-CoA esters; passage across the membrane requires L-carnitine as a transporter. On the inside of the mitochondrial membrane, the acyl-CoA esters are made available to be metabolized through the process of beta oxidation. One of the key metabolic byproducts of this process is acetyl-CoA, also called "active acetate," which enters the Krebs cycle (also known as the "citric acid cycle") to supply fuel for production of ATP, the cell's primary energy "currency." L-Carnitine shuttles excess fatty acid residues out of the mitochondrion and in this role is essential for preventing toxic buildup of fatty acids inside the mitochondrion.