What is L-Carnitine and Can It Help You Lose Weight and Boost Performance?
L-Carnitine is often marketed as a weight loss supplement and more. This compound can indeed be beneficial, but only under specific conditions.
L-Carnitine supplements may be useful, but their effectiveness depends on certain factors.
Understanding L-Carnitine
L-Carnitine is a nitrogen-containing compound found in nearly every cell of the body, especially abundant in skeletal muscles and the heart muscle.
Its primary role is to transport long-chain fatty acids across the mitochondrial membrane—the cell's powerhouse—where these fats are oxidized to produce energy. Simply put, it delivers fuel to the cell's energy centers.
Additionally, L-Carnitine helps clear toxic byproducts from these organelles, preventing the buildup of cellular waste.
Most healthy individuals do not experience L-Carnitine deficiency because it is obtained through diet and synthesized in the liver and kidneys from amino acids lysine and methionine.
Deficiencies are rare and typically occur in cases such as kidney failure or during certain antibiotic treatments.
Does L-Carnitine Really Aid in Weight Loss?
L-Carnitine supplements are widely promoted as fat-burning aids and are common ingredients in many weight loss formulas.
Since L-Carnitine facilitates the use of long-chain fatty acids as muscle fuel, it is hypothesized that regular intake might enhance fat oxidation.
However, several studies have shown that even high doses—up to 6 grams daily for two weeks—do not increase muscle L-Carnitine levels, nor do they affect fat oxidation or energy expenditure at rest or during exercise.
The only scenario where muscles accumulate more L-Carnitine is when it is taken alongside carbohydrates. Insulin promotes the storage of this compound, but this approach is counterproductive for weight loss.
Even if fat oxidation slightly increases over time, a calorie surplus and high insulin levels will prevent effective weight loss.
Nevertheless, a review of nine scientific studies concluded that L-Carnitine supplementation could lead to an average weight loss of 2.9 pounds (1.33 kg). Notably, these studies involved individuals with obesity or significant overweight, and in five of them, participants had diabetes.
A more recent meta-analysis of 37 studies found that L-Carnitine might reduce weight by an average of 2.6 pounds (1.2 kg), but it showed no significant impact on waist circumference, body mass index, or body fat percentage.
In summary, L-Carnitine may offer modest weight loss benefits primarily for people with obesity or substantial excess weight. If your BMI is within a normal range and you're aiming to tone up or lose belly fat, L-Carnitine is unlikely to be effective.
Can L-Carnitine Enhance Athletic Performance?
A meta-analysis of 11 studies revealed that L-Carnitine supplementation can improve performance, but only during high-intensity exercise. The supplement can be taken as a single dose or over an extended period.
Key findings include:
- Six months of daily intake of 2.7 grams alongside 160 grams of carbohydrates improved performance during intense cycling at 80% of maximal oxygen consumption (VO2 max).
- Nine weeks of 2 grams daily increased repetitions in strength exercises, total training volume, and peak power output during cycling tests.
- A single dose of 3 grams taken 1.5 hours before testing enhanced peak power in cycling sprints.
- Consuming 3–4 grams an hour before exercise delayed lactate buildup and fatigue onset during running speeds between 5 to 10.5 mph (8 to 17 km/h).
However, L-Carnitine does not improve performance in lower-intensity workouts.
Does L-Carnitine Speed Up Recovery?
Some evidence suggests that L-Carnitine may aid recovery by acting as an antioxidant.
For instance, a study found that taking 2 grams daily for two weeks before a 14-kilometer run helped young men recover faster.
Participants showed enhanced antioxidant defense and significantly lower muscle damage markers 24 hours after intense exercise.
Similar results were observed in another study involving strength exercises, where young men taking L-Carnitine for three weeks experienced less muscle damage after multiple sets of squats.
Additional research with men and women aged 45–50 showed that a three-week course of 2 grams daily improved recovery and reduced muscle soreness after resistance training.
Despite these promising findings, more comprehensive analyses, such as meta-analyses, are needed to firmly establish L-Carnitine's role in recovery.
Are There Any Side Effects of L-Carnitine?
Daily doses of 3 grams may cause nausea, vomiting, abdominal pain, diarrhea, and a fishy body odor.
In one study, five women taking 2 grams twice daily dropped out due to nausea and diarrhea.
Another concern involves excessive trimethylamine N-oxide (TMAO), a byproduct of L-Carnitine metabolism by gut bacteria.
High TMAO levels are linked to increased risk of atherosclerosis and cardiovascular diseases, so excessive L-Carnitine intake, especially in those consuming large amounts of red meat, is not advisable.
Who Should Consider Trying L-Carnitine?
L-Carnitine supplementation might be worth trying if you:
- Are struggling with obesity and want to lose weight, keeping in mind that expected weight loss is modest (around 2 pounds). Diet and exercise remain more effective.
- Engage in high-intensity sports training (above 80% VO2 max), where the supplement can boost power and delay fatigue.
- Seek faster recovery after intense workouts.
If you have a normal weight and perform low to moderate intensity exercise, L-Carnitine supplements are unlikely to offer benefits.
Choosing and Using L-Carnitine
Sports nutrition markets several forms of L-Carnitine: L-Carnitine L-tartrate (combined with tartaric acid), acetyl-L-carnitine, and propionyl-L-carnitine.
Studies indicate that acetyl and propionyl forms are absorbed more slowly and eliminated faster than pure L-Carnitine.
One study found that only L-Carnitine L-tartrate had any effect on weight loss in people with type 2 diabetes, while acetyl and propionyl forms showed no results.
Regarding athletic performance, most research uses L-Carnitine L-tartrate, making it the preferred choice for those aiming to increase power, delay fatigue, or speed recovery.
Most manufacturers recommend a daily dose of 2 grams, and considering potential side effects, it’s best to follow these guidelines.
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