SUPPLEMENT SERIES: L-CARNITINE

L-carnitine (L-3 hydroxytrimethylaminobutanoate) is an amino acid whose name comes from the Latin word carnus, which means meat, from which it was first isolated. It can also be synthesized in the body from the essential amino acids lysine and methionine.

Though not essential itself, L-carnitine is considered conditionally essential for many people who aren’t synthesizing as much as they need, such as those with angina or intermittent claudication. It plays an essential role in the transport of fatty acids into the mitochondria (the powerhouses of the cell) for oxidation and energy production.

Due to its fat burning role in the body, carnitine has been thought to be beneficial as a weight loss supplement and as a sports performance aid (to increase available energy and to spare glycogen). Therefore, researchers have investigated possible benefits that consuming L-carnitine could have on recovery from exercise, weight loss, and athletic performance.

RECOVERY

Strong evidence exists for carnitine as a recovery product. Several studies have indicated that carnitine supplementation can reduce muscle damage after exercise [1-3], even after as little as 2 weeks of consumption.

Both endurance and resistance exercise were utilized in the muscle damage studies, and various markers for recovery were measured, including MRI scans for muscle damage, creatine kinase (a biomarker used to measure muscle damage), and perceived soreness.

A decrease in oxidative stress was also observed with carnitine use [2-4], after both chronic and acute supplementation. The antioxidant activity could also improve recovery after strenuous exercise, since exercise raises oxidative stress.

WHAT ABOUT WEIGHT LOSS?

Since carnitine plays such an important role in fat burning, it makes sense that people would take it for weight loss and fat loss. However, not all studies agree that carnitine promotes weight loss.

  • Four weeks of carnitine supplementation at 1 gram per day significantly increased weight loss in conjunction with a weight loss diet over the diet alone in a study of 100 obese subjects [5].
  • In another study, eight weeks of carnitine supplementation at 4 grams per day did not induce changes in total body mass, fat mass, or fat burning at rest in overweight women [6].
  • Also, taking 2 grams of carnitine before and 2 grams during a marathon run did not increase fat burning in young, healthy men [7].
  • However, studies in elderly people and animal models have demonstrated fat loss benefits [8-10].

In all, the research suggests that carnitine can induce fat loss, but more evidence is needed to determine the precise dosage and supplementation period for fat loss in young, healthy people, and how different diets may affect the action of L-carnitine.

PERFORMANCE BENEFITS

Employing a 6-month supplementation period, Wall and colleagues were able to induce improvements in performance [11].

  • Work output increased 11% during a 30 minute “all-out” performance test on a bicycle.
  • Skeletal muscle metabolites were tested during low-intensity and high-intensity exercise bouts to elucidate how carnitine might be working.
  • After the low intensity exercise, muscle glycogen content was 35% greater in the carnitine group, indicating that carnitine may spare glycogen for endurance athletes.
  • After the high-intensity exercise, carnitine supplementation induced lower muscle lactate, which indicates that more carbohydrates are being burned more efficiently (aerobically), and suggests that high-intensity athletes may also have more fuel later in the competition.

Other researchers have induced performance benefits after acute carnitine supplementation using a time to exhaustion cycling test [12] and sprints on a bicycle [13]. However, many studies did not observe performance benefits.

  • After 2 weeks of carnitine supplementation, no differences were observed in healthy, active men during a time trial test [2].
  • Similarly, 3 weeks of carnitine consumption did not improve squat and leg press [3].
  • Taking carnitine directly before exercise did not improve marathon run time [7], sprint times [14], bench press reps to failure or bench press power [4].

Though some studies have not demonstrated performance benefits from L-carnitine supplementation, it is important to note that the dosage and supplementation period have not been consistent among studies, and these two factors are essential to increase carnitine in the muscle.

WHO SHOULD/SHOULD NOT TAKE IT?

Athletes of all types and levels could benefit from carnitine use. Endurance athletes interested in performance enhancement will need to ensure that they are taking an adequate amount of carnitine daily for a long period of time. High-intensity athletes and endurance athletes alike would benefit from the antioxidant activity and the reduction in muscle damage.

SIDE EFFECTS

There are no known side effects with carnitine supplementation. Individuals supplemented with 4 grams for 24 weeks with no medical issues [11]. Some people have noticed a fishy body odor when consuming 3 grams per day.

DOSAGE

Though some studies have tested doses as large as 4.5 grams, most studies agree that the effective dose is 1-2 grams per day. This dose has been demonstrated to benefit recovery, fat burning, and exercise performance.

For carnitine supplementation to exert maximal benefit for athletes, it must get into muscle tissue. Though studies have demonstrated increases in circulating carnitine, muscle carnitine content has often remained unaltered at shorter supplementation periods [15,16].

In one study, muscle carnitine content increased 21% after consumption of 2g of L-carnitine L-tartrate with carbohydrate daily for 24 weeks [11], suggesting that a long period of supplementation may be necessary to increase muscle carnitine and thereby maximize benefit for athletes.

BOTTOM LINE

Carnitine is effective at improving recovery after both endurance and resistance exercise by lowering oxidative stress and muscle damage.

Carnitine also increases fat burning and may increase fat loss over time, but more research is needed in a variety of populations.

Improvements in metabolism occurred at low and high intensity endurance exercise, such that a wide variety of athletes could benefit from carnitine supplementation; however, long periods of supplementation should be employed to see these benefits.

ABOUT THE AUTHOR

Paul Falcone, MS, CISSN, is a certified sports nutritionist (ISSN). He was awarded a Master’s degree in Nutrition after completing research on fish oil supplementation in an animal model of chronic disease.  He works as a research coordinator at MusclePharm Sports Science Institute in Denver, CO.

REFERENCES

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