A naturally occurring compound produced by the body and available as a supplement, l-carnitine supports brain function and aids weight loss, according to some claims. But, does the evidence stack up? Read on to discover more.
Supplements that claim to shift the pounds and slim our waistlines are understandably attractive, but before you spend, it’s important to understand the science and whether a particular supplement is appropriate for your circumstances.
What is l-carnitine?
Carnitine is the generic term used for several compounds: l-carnitine, acetyl-l-carnitine and propionyl-l-carnitine. Carnitine is an amino acid derivative (a building block of protein) made by the body in the liver, kidneys and brain, from two other amino acids, lysine and methionine. For your body to make sufficient amounts, you also need adequate amounts of vitamin C, iron and vitamins B3 and B6. Carnitine is not considered an essential amino acid because the body can make what it needs. We also obtain carnitine from the foods we eat, especially those of animal origin.
One of the benefits of carnitine is that it helps convert the foods we eat into energy; it’s especially important for its role in taking long chain fatty acids into energy producing sites known as mitochondria. Carnitine also appears to influence the heart, as well as muscle mass.
The benefits of carnitine include:
• May improve fat loss
• May increase muscle mass
• May support energy production in the heart
• May improve exercise performance
• May improve male fertility
• May aid brain function
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6 potential benefits of l-carnitine
1. May improve fat loss
L-carnitine is often used as a diet aid because it supports the transportation of fatty acids into the energy-producing mitochondria. In doing so, it helps us use fat for energy, especially when we combine it with exercise. Studies suggest this may have a modest improvement on body weight, body mass index and fat mass, but appears to have little impact on our waist circumference or body fat percentage. These somewhat conflicting results mean larger, more comprehensive studies are needed to determine whether l-carnitine can be relied upon to positively impact weight, and in particular fat loss, in all people.
2. May increase muscle mass
One study looking at the effect of 24 weeks of l-carnitine supplementation on muscle strength and mass in healthy women reported an increase in muscle mass, but no change to muscle strength. Some claims also suggest it may improve muscle repair and recovery post-exercise.
3. May support energy production in the heart
There are conflicting findings on the effects of l-carnitine on the heart and whether it is helpful or harmful – some studies suggest it may reduce inflammation and help produce energy in the heart muscle, especially for those with hypoglycaemic-induced high blood pressure. However, these effects may be gender-specific, being potentially less likely to occur in men.
4. May improve exercise performance
L-carnitine may support exercise performance because it may help preserve muscle glycogen, promote fat use and spare the use of amino acids as energy sources, allowing them to be used to make new protein instead. L-carnitine may also reduce the accumulation of lactate, and by doing so, enhance recovery time and reduce muscle soreness, enabling exercise enthusiasts to train harder. That said, evidence for these findings is not conclusive, and more studies are needed.
5. May improve male fertility
Taking l-carnitine by mouth and/or in conjunction with acetyl-l-carnitine appears to increase sperm count and motility in men with fertility issues, potentially improving fertility rates.
6. May aid brain function
To date, results are mixed, with one 2018 study reporting 1500mg of l-carnitine (as acetyl-l-carnitine) taken daily for 28 weeks improved brain function in those with dementia. However, an earlier review reported no improvement in reaction time, immediate memory or delayed recall in young adults with cognitive impairment. Therefore, more research is needed before conclusions can be drawn.
Potential side effects
Possible side effects of supplementary l-carnitine include, but are not limited to:
• Gut disturbance: l-carnitine does not have an established upper intake level, although doses above 3g per day may cause nausea, vomiting, abdominal cramps and diarrhoea
• Coronary artery disease: some research suggests l-carnitine may be linked to an increased risk of coronary artery disease and heart failure, especially in men and those who eat meat. This may in part be because gut bacteria metabolise l-carnitine into a compound called trimethylamine-N-oxide (TMAO), which is known to cause furring of the arteries and potentially lead to atherosclerosis
• Thyroid function: taking l-carnitine as a supplement can make the symptoms of a low-functioning thyroid worse
• Muscle weakness and seizures: high amounts of l-carnitine may cause muscle weakness in those with chronic kidney disease and may increase the risk of seizures in those with seizure-related disorders
Food sources of carnitine
There are many natural food sources of carnitine; most, but not all, are of animal origin, including:
• Beef
• Lamb
• Chicken
• Cod
• Dairy foods, including milk and cheese
• Mushrooms, avocado and asparagus
• Wholemeal
• Flaxseeds
How do you take l-carnitine?
Carnitine found in food is safe and there is no defined upper limit; however, when taken as a supplement, the appropriate dosage may depend on the form taken. For example, studies suggest taking 3g or more per day may be enough to initiate side effects.
There is no dietary reference value for l-carnitine, but the body needs about 15mg per day – this is typically a combination of carnitine made by the body and obtained from the diet. An average adult eating a balanced omnivorous diet should obtain between 24-145mg daily from dietary sources, although the equivalent vegan diet may provide much less, at only 1.2mg carnitine. Healthy children and adults make all the carnitine they need; however, those with end-stage kidney disease or on dialysis, premature babies and people with a rare genetic disorder known as primary carnitine deficiency may have low levels.
It should be noted that there is insufficient evidence regarding the safety of l-carnitine as a supplement during pregnancy, and although small amounts may be safe during breast-feeding, large doses should be avoided. Those taking prescribed medication including valproic acid and other anti-convulsant medication should discuss the impact of their medication on carnitine levels with their prescribing practitioner. Certain antibiotics may also affect carnitine levels and the efficacy of anti-coagulants may be increased.
Does l-carnitine work without exercise?
L-carnitine may help support fat use without exercise, but is considered to be more effective when combined with physical activity.
Overall, is it worth taking l-carnitine?
Most of us are able to make or consume the carnitine we need, although those with kidney disease, certain genetic disorders or who follow restrictive diets may be at risk of lower levels. Furthermore, more studies are needed to determine the safety and effectiveness of l-carnitine when used as a supplement.
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