Carnitine is an amino acid that is either consumed in the diet or synthesized by the body from other essential amino acids. It participates in energy metabolism by transporting long-chain fatty acids, particularly triglycerides, to the body cells where they are broken down for fuel for body tissue. It is produced in the liver and kidneys and stored in the skeletal muscles, heart, brain and sperm.
Red meat, particularly lamb, and dairy products are the most abundant sources of carnitine in the American diet. Other foods containing carnitine include poultry, fish, tempeh, wheat, asparagus, avocados and peanut butter.
Carnitine for Weight Loss
Because of its participation in fat-burning, carnitine is often included as an ingredient in weight loss supplements. It is also thought to reduce feelings of hunger, which could lead to a decreased calorie intake. The research is mixed on carnitine's effectiveness as a weight loss supplement.
Some animal studies have found that mice given L-carnitine supplements had a decrease in the amount of abdominal fat stored and decreased serum leptin levels. Leptin is a hormone that is associated with obesity. A small study on human participants found that those given carnitine supplements had a 10-pound greater weight loss over the course of 12 weeks.
However, to date, most research has not shown a substantial link that increasing the amount of carnitine in the diet will increase the body's ability to burn fat or lose weight.
Carnitine for Exercise Performance
Some nutritional supplements promote carnitine as a recommended product to improve exercise or decrease muscle fatigue. Carnitine is used as a fuel by both the skeletal and heart muscle, so the body needs an adequate supply for physical activity. Improving the effectiveness of exercise can lead to weight loss by increasing the amount of calories burned during a workout session. The National Institutes of Health has compiled twenty years of research and found that carnitine supplements have not been shown to increase the body's use of oxygen, improve metabolic status while exercise, or increase the amount of carnitine stored in muscle tissue.
The Bottom Line
Because most American diets are sufficient in carnitine, taking additional supplements is not appropriate for most people. Most studies have failed to show a link in carnitine supplementation and weight loss or exercise enhancement.
However, L-carnitine supplements do appear safe for most people. The typical dose is 500 to 1000 milligrams, taken three times a day. High doses, approximately 5 grams a day or more, can lead to side effects such as nausea, vomiting, abdominal cramps, diarrhea, insomnia and a "fishy" body odor.
Carnitine supplements can also interfere with certain medications, so it important to check with your personal physician before taking any weight loss or other nutritional supplemental product. For example, many women with thyroid disorders have difficulty losing weight, but carnitine supplements should not be taken, as it can further impair the action of the thyroid.