You'll often see carnitine supplements touted as a way to lose weight and boost exercise performance. This amino acid derivative helps you metabolize the food you eat into energy, so the theory seems to make sense. However, the jury is still out on this possible benefit, according to the University of Maryland Medical Center, or UMMC. Always consult a doctor before trying a new supplement.
Significance
Carnitine helps your body turn fat into energy. Your body can usually make all the carnitine it really needs. It's produced by your kidneys and liver and stored in your heart, muscles, brain and sperm. Though it's marketed as a weight loss supplement, no scientific evidence supports claims that it helps with weight loss, according to UMMC. There's also no evidence that it boosts exercise performance, the experts at the center note.
Expert Insight
While people marketing carnitine as a supplement often refer to studies proving its worth in terms of energy metabolism and athletic performance, the reality is that such evidence is based on small and uncontrolled studies rather than reliable clinical trials, according to Oregon State University. Problems with this research include lack of appropriate control groups, small numbers of participants and short durations of supplementation. Also, most studies as of 2010 show that L-carnitine supplementation has no effect on physical performance and failed to demonstrate that supplementation increases carnitine levels in your skeletal muscle, which is where more than 95 percent of your body's total carnitine is stored. A few of the studies do show that oral carnitine increases muscle mass, reduces fat mass and reduces fatigue, which leads to the theory that the supplement may contribute to weight loss, according to UMMC.
Considerations
If you are taking carnitine in attempt to lose weight, you may want to seek it from foods instead of taking a supplement. Your body easily absorbs L-carnitine from food. However, your body's absorption of oral L-carnitine supplements is much lower. In fact, bioavailability of L-carnitine from supplements may be as low as 14 to 18 percent of the total dose, according to Oregon State University. In contrast, you can absorb 63 to 75 percent of the L-carnitine contained in food. Supplement doses generally range from 500 mg to 2,000 mg per day.
Potential
If you are seeking L-carnitine from dietary sources, you'll want to eat fish, poultry, meat and dairy products, which are the richest sources, according to OSU. Grains, fruits and veggies have little of this nutrient. Beef steak or ground beef each have about 80 mg per 3 oz. serving. Pork has 24 mg, cod 5 mg and chicken 3 mg for the same size serving. A cup of milk contains 8 mg.
Side Effects
Taking a carnitine supplement to boost athletic performance or lose weight may cause side effects, though no toxic effects due to L-carnitine overdose have been reported, according to OSU. These supplements may lead to mild gastrointestinal symptoms such as diarrhea, nausea or vomiting and abdominal cramps. If your supplement provides more than 3,000 mg carnitine daily, you may have a "fishy" body odor. Acetyl-L-carnitine, which is available as a nutritional supplement without a prescription, may increase seizure severity and frequency if you have seizure disorders. Also, if your supplement has a mixture of D- and L-carnitine, know that the D-isomer may actually increase the risk for carnitine deficiency because it competes with L-carnitine for absorption and transport. Supplements containing such a mixture have led to reports of muscle weakness in people with kidney disease, according to OSU.
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