Without acetyl-L-carnitine, the mitochondria can't absorb and metabolize fatty acids. This process has led to the claim that acetyl-L-carnitine can aid in weight loss.
There is little actual proof to support that claim, or the claim that acetyl-L-carnitine can lead to a better fat-to-muscle ratio. The supplement may improve the endurance of patients with emphysema (also known as COPD, or chronic obstructive pulmonary disease), and relieve the fatigue associated with fibromyalgia and celiac disease [source: NAT]. If you're already adhering to a substantial exercise program, though, there's no proof that acetyl-L carnitine will make a difference in your results.
It is somewhat more promising as a treatment for certain neural disorders. Acetyl-L-carnitine contains an acetyl group that is essential for the production of a key neurotransmitter [source: UMHS]. The nervous system depends on fat metabolism. Fat is a major component of the myelin sheath that coats each nerve cell. The chemical composition of the myelin sheath is what allows impulses to jump across synapses (the spaces between nerve cells) and travel through the body to turn into actions, sensations, ideas or feelings. The breakdown of the myelin sheath can prevent the nervous system from being able to communicate effectively with itself. That's what happens in diseases such as multiple sclerosis. A myelin sheath with a high fat content performs more effectively, insulating the nerve and allowing the impulse to travel faster [source: Nagel].
Because of the way acetyl-L-carnitine seems to aid in fat metabolism, some doctors believe it shows promise as a treatment for certain nervous and cognitive disorders. Among these disorders are dysthymia (mild depression), attention deficit and hyperactivity disorder (ADHD) Alzheimer's disease, the neural degeneration associated with cirrhosis and obsessive-compulsive disorder (OCD) [sources: Arnold, NAT]. Acetyl-L-carnitine has been studied as a way to reduce the hyperactivity associated with fragile X syndrome, a serious genetic disorder, but results are inconclusive [source: NAT].
Some complications of diabetes also impair the nerves. Certain doctors consider acetyl-L-carnitine a promising candidate for repairing the damage wrought by diabetic neuropathy, a harrowing complication that erodes nervous function in the arms and legs -- and sometimes in the heart -- leading to pain and numbness. But clinical proof is lacking, and at least one study indicates that carnitine supplements might actually hurt diabetics by increasing blood triglyceride levels (the amount of fat in the circulatory system) [source: NAT].
What do we definitely know about the benefits of acetyl-L-carnitine? Read on.