Weightloss and Performance

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L-Carnitine is often used in bodybuilding circles as a weight loss supplement and to a lesser extent, a performance enhancer in endurance athletes. With its popularity, several scientific studies have been performed to test the anecdotal L-carnitine benefits proposed for improving weight loss and athletic performance.

L-Carnitine Explained

L-Carnitine is an amino acid like compound produced in the body from the amino acids lysine and methionine. It is found almost found exclusively in muscle tissue. Unlike other amino acids, carnitine is not directly involved in the synthesis of tissue proteins. Instead, it plays an important role in the muscle energy system where it aids in the metabolism of fatty acids for fuel. It is found in a wide variety of foods, but the highest concentrations are in meat and dairy products.

Proposed L-Carnitine Benefits

L-carnitine is sold in the hope that it will help shuttle fatty acids to the mitochondria to be metabolized in the muscle cell as fuel instead of being stored as fat. So in theory supplementing with L-carnitine will increase your ability to burn more fat. L-carnitine may also serve as an antioxidant, helping buffer some of the free radicals produced in cell metabolism.

As we age, L-carnitine levels tend to decline and some theorize that this may contribute to age-related reduction of metabolic efficiency. Studies suggest that supplementing the elderly with carnitine may improve energy metabolism.

L-Carnitine And Weight Loss

For example, 36 moderately over weight women supplemented with 4 grams of L-carnitine for 60 days. This double blind placebo study found no significant difference in body weight, lean body mass, or fat oxidation. The full study can be found here: L-Carnitine Benefits.Few studies have been performed on carnitine for the purposes of boosting fat loss. Those that have been done have conflicting conclusions. The general consensus is that people in western countries get enough carnitine and its constituents for synthesis through diet for the carnitine shuttle to work.

 L-Carnitine And Performance

Given the importance of carnitine in the muscle cell energy cycle, it has been long been supplemented by athletes and bodybuilders. However, studies have shown conflicting results. This may be due to difficulties in overcoming the body’s normal regulation of cellular carnitine levels.

Carnitine has been shown to increase performance in athletes with training experience. It makes sense to conclude that L-Carnitine can be useful for those individuals where minor changes in maximal oxygen consumption could result in significant performance improvements. So in layman’s terms, for competitive endurance athletes like runners or cyclists.

Once such placebo controlled study looked at acute (single dose) and extended cartinine supplementation in elite male and female athletes. These athletes participated in either kayaking, rowing, or weightlifting. Training and nutrition intake were controlled. Subjects in the extended trial, took 4 grams for 21 days. The acute study, subjects took a single 4 gram dose. Subjects in the extended trial saw improvements in both the strength index and maximal oxygen consumption scores compared to placebo. Metabolic improvements were also seen in serum free fatty acids and triglyceride levels. Similar metabolic improvements were seen in the acute trial 90 minutes after ingestion. You can find the study here: L-Carnitine and Elite Athletes.


So are there really L-carnitine benefits that make it worth buying and using? Yes, but only for the select few that are trained endurance athletes where a small increase in performance can mean the difference between 1st and last place.

If you are looking to use L-carnitine as a weight loss aid, it is simply not that effective in people with normal metabolisms. So the L-carnitine benefits for fat loss are just not supported in the research.


Based on the research studies, the average dosage per day is 2-4 grams.

Side Effects

L-Carnitine is tolerated well in studies. Some users experience stomach problems like nausea or diarrhea. If you experience any side effects, stop supplementing immediately.