Carnitine Fails Short-Term Test As Endurance-Enhancing Supplement
WASHINGTON (AP) _ A couple of weeks of taking the popular food supplement carnitine doesn’t improve exercise endurance, a study indicates.
Even relatively high doses resulted in no change, the study said.
Carnitine carries fatty acids into the part of the cell in which they can be broken down for fuel. As a result, some athletes believe that supplements may help them burn more fat.
This, they believe, will make them leaner while giving their cells something to use besides glycogen, the form of sugar that’s the muscle’s prime aerobic energy source. The added fuel could theoretically delay fatigue.
The study in the American College of Sports Medicine journal Medicine and Science in Sports and Exercise looked at whether supplements would increase fatty acids in muscle cells.
Researchers at Ball State University in Muncie, Ind., studied eight men with an average age of close to 27. All got six grams a day of carnitine, which they drank in orange juice.
This dosage was high enough to produce a side effect - half of the men developed diarrhea, said former Ball State researcher Matthew D. Vukovich, of Wichita State University.
The men also got a hefty amount of potential fuel to digest: a shake of heavy whipping cream and chocolate ice cream, with 95 grams of fat.
The researchers wanted to see if carnitine might work better if the body was given extra help in metabolizing the fat. So the men also got heparin, which makes the body release an enzyme that breaks down fat.
Researchers had the men exercise on a stationary bike, at a vigorous 70 percent of their aerobic maximums. The subjects took two hour rides - one with heparin and carnitine, and one with carnitine alone.
The researchers took small samples of blood and of muscle tissue before, during and after exercise. They found more carnitine in the blood, but no more where it would do good - in the muscle.
There also was no drop in the amount of glycogen being used, indicating the muscles were getting no benefit from the extra fat, the study said.
This indicates extra carnitine doesn’t help muscle cells feed, said Vukovich.
Nor did the men’s ability to exercise on the stationary bikes improve, either in the carnitine alone or carnitine-with-heparin tests, the study said.
One 1991 study in Italy did find extra carnitine in the muscle, but that was with people taking the supplement for 120 days, Vukovich said.
This kind of usage would be unusual, Vukovich said: ″People usually don’t take it for that long. They want to take it for a short period, get the effect, and get off.″
Although carnitine has a wide following, especially in Europe, ″we couldn’t justify it was doing what they claimed,″ said David L. Costill, director of Ball State’s Human Performance Laboratory.
That’s probably because a healthy body already has plenty of carnitine, which people can get from red meat, said Vukovich. ″It’s very unusual for a person to be carnitine deficient,″ he said. ″The body spares it; if it doesn’t get (carnitine), it excretes it less.″
″You usually have a five- to tenfold excess in most tissues,″ said a veteran researcher on carnitine, Loran L. Bieber, associate dean for research in the College of Human Medicine at Michigan State University, East Lansing.
For getting fatty acids into the cell’s powerhouse, the mitochondria, carnitine is ″absolutely essential,″ Bieber said. ″But the amount needed isn’t very great.″
If the body gets too much carnitine, the surplus is excreted, said Nancy Rodriguez, an assistant professor of nutritional sciences at the University of Connecticut.
The Ball State study was funded by a Swiss-based company, LONZA Ltd. It wanted to put carnitine, which is one of its products, to the scientific test, Costill said.
Besides endurance athletes, many body builders also use carnitine, hoping it will help them burn body fat, said Janet Wallberg Rankin, an associate professor of exercise science at Virginia Tech, Blacksburg. ″There is virtually no research on carnitine in this population to see if it works,″ she said.
″Supplement companies also try to market this ‘fat burning’ idea of carnitine for weight loss for ‘normal’ folks, too.″ she said.
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