Where it comes from: Carnitine (and L-carnitine) is a nutrient that helps the body break down fat and turn it into energy. It also increases the activity of certain nerve cells in the central nervous system. Carnitine is an amino acid naturally produced by the body in the liver and kidneys and stored in the skeletal muscles, heart, brain and sperm. The nutrient also occurs in fish, poultry, red meat and some types of dairy.

What it’ll do for you: “Marketers will tell you it’s a miracle pill that will speed up the way your body burns fats but there have been no credible studies that give weight to that claim,” says Lisa R. Young, Ph.D., R.D., author of The Portion Teller and adjunct professor of nutrition at New York University. Here, a closer look at that claim and other ones that may be relevant to you:

  • Helps with weight loss
    L-carnitine is often sold as a weight loss tool, and some studies show that oral carnitine can reduce fat mass, increase muscle mass and reduce fatigue—three things that may contribute to weight loss. However, the University of Maryland Medical Center and the Linus Pauling Institute say there is no proof that supplementing L-carnitine in healthy individuals will improve fitness.
  • Protects against heart disease
    Much of the body’s carnitine is stored in the heart, which makes sense since the heart relies on fatty acids as fuel to pump blood. With that in mind, many studies have found that L-carnitine supplements can improve muscle weakness and help the heart function more efficiently—particularly for those who have been diagnosed with heart disease. The most promising research supports L-carnitine supplements for patients with angina, as the nutrient has proven to help some suffers exercise without chest pain. Small studies suggest that those who take L-carnitine supplements soon after a heart attack may be less likely to suffer another heart attack, die of heart disease, experience chest pains or develop heart failure. Another study at Minneapolis VA Medical Center found that carnitine can improve exercise capacity in people with heart failure. In each case, however, other studies have found no positive effects and further research is needed. Note that these studies all prove effectiveness in patients who already have a record of heart conditions. “If you have a failing heart muscle, adding levels of carnitine may be beneficial to the organs,” begins Young. “But if you’re healthy, there’s no heart benefit to come of taking these supplements.”
  • Can improve sperm count and sexual health
    While low sperm counts have been linked to low carnitine levels in men, several studies suggest that L-carnitine supplementation may help increase count and mobility. A double-blind study of 86 infertile men found that two grams of L-carnitine supplements per day for two months led to significant improvements in sperm quality. On a semi-related note, an Italian study suggests carnitine can also help improve the effectiveness of sidenafil (Viagra) in men with diabetes who had not previously responded to the drug.
  • Helps ease the aging process
    Various studies have found that low levels of carnitine contribute to aging and may be reversed or slowed by acetyl-L-carnitine. A few small clinical trials suggest that carnitine supplements (two to three grams per day for six to twelve months) might slow the cognitive decline in Alzheimer’s patients. However an additional study of 167 early-onset patients found that the supplements had no significant effect on cognitive decline and more research is needed.

Suggested intake: “Our bodies make carnitine so healthy men don’t need the supplement,” says Young. “Even men with poor diets, who tend to only eat, say, burgers get enough carnitine—it’s the one good thing about beef.” Meaty diets have been found to provide 20 to 200 milligrams per day of L-carnitine for a 154-pound male, while veggie diets provide as little as one milligram per day. Fruits, vegetables and grains obviously contain very little L-carnitine, and in addition to meat, other big sources are poultry, fish and dairy products.

A healthy individual will normally produce enough L-carnitine to provide the body with all it needs to convert fat to energy. According to the Linus Pauling Institute, L-carnitine supplements are safe at levels between 500 and 1,000 mg a day. The Mayo Clinic reports little reason for concern regarding the safety of the supplement.

Between 63 percent and 75 percent of L-carnitine from food is absorbed. However, only 14 percent to 20 percent is absorbed from oral supplements. There are two types of carnitine supplements worth noting: oral L-carnitine and acetyl-L-carnitine. The latter provides L-carnitine and acetyl (shocking, we know!), which is used in the formation of neurotransmitters.

Associated risks/scrutiny: L-carnitine appears to be well tolerated, but as always, doctors should be consulted before you begin any supplement routine. “Especially because carnitine may interfere with certain medications,” points out Young. L-carnitine supplementation may cause mild gastrointestinal symptoms, including nausea, vomiting, abdominal cramps and diarrhea. Supplements providing more than 3,000 mg per day may cause a gross, “fishy” body odor.

Back to The Men’s Fitness Supplement Guide

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