Should cyclists supplement with carnitine?

Key claims about carnitine

Carnitine is best known in the bodybuilding community as a fat burner. But there are many more claims surrounding this supplement that could be of interest to cyclists. Here is a list of the most important ones.

• It enhances fat metabolism
• Reduces body fat
• Increases muscle mass
• Increases VO2max and reduces lactic acid production during intense exercise
• It enhances endurance by increasing fat oxidation and preserving muscle glycogen

The problem with carnitine

Carnitine is involved in the process of burning fat for energy. During fasting or low- to moderate-intensity endurance rides, fat is the primary source of energy. Fat molecules must be transported to the mitochondria, which are the powerhouse of the cell, where it is converted into usable energy. That’s where carnitine helps. The problem is that muscles have about 1,000 times higher concentration of carnitine than blood.

To move carnitine from the blood to the muscles, our body uses a transport protein called OCTN2. But there is a limit to how much carnitine OCTN2 can move. Even if we take extra carnitine as a supplement, it usually does not increase the amount in our muscles. If we can’t get more carnitine into our muscles with a supplement, it can’t produce the claimed results.

Carnitine as a weight management tool

Several studies have shown that oral carnitine intake does not alter muscle carnitine levels. Even direct injection of carnitine failed to increase its concentration in the muscles. Carnitine supplementation was unable to increase muscle carnitine concentration in these studies for more than one reason:

• Only 20% of the 2-6 g dose was absorbed
• Carnitine transport into muscle was limited

This would mean that carnitine cannot produce any of the claimed fat burning benefits. However, there may be a solution to low carnitine intake. Some studies suggest that muscle carnitine levels can increase if carnitine is consumed when insulin levels are high. This strategy involves daily carnitine supplementation accompanied by a high carbohydrate intake. While this method can increase muscle carnitine, it is not very practical for weight loss. High carbohydrate intake may even lead to weight gain rather than increased fat oxidation and loss.

Carnitine for cycling endurance

If carnitine supplementation could successfully increase muscle carnitine levels during exercise, then it could enhance fat oxidation during exercise, preserving muscle glycogen and delaying fatigue. This is how it could theoretically be beneficial for cyclists looking to build endurance. An early study showed that after 14 days of consuming 4-6 grams of carnitine per day, there was no increase in muscle carnitine levels during high-intensity sprint cycling.

A different study showed that prolonged supplementation with carnitine tartrate alongside carbohydrates increased muscle carnitine. It also showed that glycogen was spared during low-intensity exercise, suggesting increased fat oxidation, and lactic acid accumulation was lower during high-intensity exercise. Overall, these changes were associated with an 11% improvement in a 30-minute exercise performance test.

So, should you take carnitine?

Studies show that it is really difficult to increase muscle carnitine concentrations using supplements. The only way to achieve this reliably is long-term carnitine supplementation with a very high carbohydrate intake. This may yield a modest benefit in exercise performance. When it comes to weight management, carnitine doesn’t seem like a practical supplement because you have to consume carbohydrates regularly. Overall, there is no strong motivation for carnitine supplementation for cyclists.