It’s a popular supplement that has proven to help athletes, heart patients and people with diabetes.

Fitness expert Mackie Shilstone, who works with some of the world’s top athletes, even uses it himself.

It's called Acetyl-l-Carnitine and it’s a natural chemical sold as a dietary supplement.

“I find in working with my athletes that they become, in my world, more effective. They become more efficient and I think there is a relationship with the Carnitine with the COQ-10 to improve the functioning of the energy system in the body,” said Shilstone. 

The energy factory in each cell needs Carnitine to function as it helps transform fat into energy. We get it in our diets from meats, mostly red meat, and a little from dairy. Doctors say our bodies need it to function - especially for our muscles to function best.

“That's one of the few things that actually studies are showing pretty reliably that if you take l-Carnitine it will change your muscle fat ratio in a positive direction,” said Dr. Henri Roca of the LSU Health Sciences Family Medicine Department. “It will give you more muscle and less fat.”

Mackie Shilstone said he finds it's most therapeutic for his athletes - with doctor's approval – when it’s taken an hour before a workout along with COQ-10.

So if it helps to metabolize fat for energy in athletes will it help regular people lose weight?

“There have been no compelling studies saying that it's useful for weight loss,” said Roca. “It's marketed that way but it's where the theory and the body don't always work out.”

“There was one particular study that was published in a reputable journal a year or so ago that actually studied the effects of Carnitine in obese women while they were doing exercise, which is a good study,” said Dr. Kim Edward Leblanc, the Chief of Medicine for the LSU Health Sciences Center. “Unfortunately it didn't show that they lost anymore weight with or without it.”

It is known that the more muscle you build, the faster your metabolism works and the more calories you burn even at rest. So if l-Carnitine gives you more energy and helps your muscles perform better will you will you become more efficient at burning calories?

“There are some small studies that say that endurance can be enhanced and that recovery can be enhanced by l-Carnitine,” admitted Roca. “They are not very compelling but there is some indication.”

l-Carnitine has also been successfully used in mesotherapy, which are multiple injections directly into fat cells to break them down so your body will rebuild with collagen to reshape and contour the body. And now l-Carnitine can even be found in over the counter creams with hopes of diminishing cellulite in the thighs.

On a recent Tyra Banks show four women of all ages and sizes used Nivea Good Bye Cellulite gel and patches for four weeks and swore that it worked.

“Our clinical results show the same thing,” said Alex Kowcz, the Vice-President of Research and Development for Nivea. “After two weeks the skin was firmer after four weeks the appearance of cellulite was much greatly reduced.”

Some independent doctors aren't convinced.

“There's absolutely no evidence scientifically that it works,” said Leblanc. “It would be very difficult to convince me that it does.”

“Even if it can get through, and I am not convinced much does get through,” said Roca. “Then it's going to go into the blood stream it's not going to immediately go in to the fat cells the fat cells are several layers below those layers of the skin.”

Studies show that l-Carnitine not only helps athletes perform but also helps people with heart disease and it also may help diabetics better control their blood sugar, body fat and nerve problems. It may even help with brain problems like Alzheimers, but for all l-Carnitine can do, it's not a magic weight loss supplement without exercise.