What is carnitine?
Carnitine is an amino acid that is made up of two other amino acids, methionine and lysine.
It is a nutrient that is considered conditionally essential. Meaning most of the time our body is able to produce enough endogenously to meet our needs, but in certain circumstances it must come from our food.
Carnitine plays an important role in energy production. It is found predominantly in tissues that use fat as a fuel source such as skeletal and cardiac muscle.
It transports fatty acids into the mitochondria, which is the powerhouse of the cell, so that the fatty acids can be burned to produce energy. Additionally, carnitine transports compounds out of the mitochondria that would be toxic if it was able to accumulate.
Carnitine occurs in two forms, known as D and L, that are mirror images of each other. But only L-carnitine is active in the body.
Source of carnitine
Carnitine is predominantly found in animal products including red meat. In fact the general rule of thumb is that the redder the meat, the more carnitine content it has (1).
Although, it is also found in other animal products such as dairy products and fish. Just in much lower quantities.
There are some plant based sources of carnitine but they are not particularly good sources.
To give you some perspective, adults who have a diet rich in red meat consume around 0.6-1.8g of carnitine daily whilst vegans consume around 0.1g per day (1).
Are vegans low in carnitine?
Studies have shown that plasma carnitine concentrations (carnitine in the blood), is significantly lower in vegetarians and vegans in comparison to omnivores (2,3).
Given that the majority of the carnitine in an omnivorous diet comes from red meat, it is likely that we would see the same thing in pescitarians and omnivores who do not eat red meat regularly.
Interestingly, despite having lower blood levels of carnitine, vegetarians and vegans do not have lower muscle stores of carnitine (2,3).
This is because the body is able to maintain carnitine homeostasis through several mechanisms including producing more carnitine endogenously when there is less coming in through the diet.
There is also an upregulation in renal conservation mechanisms and thus higher carnitine reabsorption may occur in vegetarians to compensate for the lower carnitine concentrations obtained from the diet (4).
A study was done looking at the effect of creatine and carnitine homeostasis in women who converted to a vegetarian diet from an regular, omnivorous diet for six-months. They found that whilst creatine stores decreased, there was no significant difference in measure of carnitine stores at three & six months (4).
Can you be deficient in carnitine?
As discussed, your body is able to maintain a balance of carnitine stores by upregulating endogenous production and reducing kidney excretion when dietary intake is low.
Your body produces enough carnitine to meet your daily needs and even if levels do fall, the body has mechanisms in place to bring it back to homeostasis.
A healthy person will rarely suffer from carnitine deficiency. Deficiency usually occurs when some kind of condition is present that affects endogenous carnitine production or carnitine homeostatic mechanisms.
Primary carnitine deficiency caused by a genetic disorder is usually identified at a young age. Although secondary carnitine deficiency can result later in life due to chronic kidney disease, HIV/AIDS, chemotherapy treatment or long term use of certain antibiotics that reduce carnitine reabsorption or increase excretion (5,6,7). In these cases, supplementation is required.
On the other hand, because carnitine production requires several nutrients that are not created by the body. A poor intake of those particular nutrients can also result in a deficiency even in a healthy person.
The first couple of key ingredients in carnitine production are lysine and methionine. These are essential amino acids, meaning that we do need to get them from our diet as the body is not able to produce them (8).
Therefore, if protein intake is very low or someone is in a state of protein deficiency, carnitine deficiency can occur.
This is also why it is important to have a range of protein sources as someone who is vegan, as most plant based protein sources do not have a complete amino acid profile.
For example, legumes tend to be low in methionine and grains tend to be low in lysine. So even if you are getting enough protein but it is mostly from legumes, you may not have enough lysine for sufficient carnitine production.
Carnitine also requires other nutrients in its production including iron, vitamin C and vitamins B3 and B6. So if you are deficient or have a low intake of any of those nutrients, carnitine production will be reduced.
For vegans, low vitamin C intake is rarely an issue due to a generally high fruit and vegetable consumption. However, iron deficiency or low iron stores may predispose some vegans to carnitine deficiency.
Although iron deficiency anemia is not more common amongst vegans than the wider population, it is still considered a nutrient of concern on a plant based diet (9).
All in all, as long as a person does not have a medical condition that affects carnitine homeostasis and has a well-balanced and adequate diet, they are not at risk of carnitine deficiency.
Carnitine Supplementation
Athletic performance
Carnitine supplementation is typically discussed in the context of sports and athletic performance. Some athletes take carnitine in hopes that it will boost their muscle carnitine stores and assist with energy production in the skeletal muscle. Very similar to what we do see occur with creatine supplementation.
However, twenty years of research has failed to find consistent evidence that carnitine supplementation can improve exercise or physical performance (10,11,12).
Even with greater doses of L-carnitine, supplementation does not result in an improved energy production when exercising nor does it necessarily increase the amount of carnitine in the muscle (11).
It has even been found that vegetarians are more resistant to storing supplemental carnitine in their muscles in comparison to omnivores.
Vegetarians and likely vegans as well, have a lower muscle carnitine transport capacity than non-vegetarians. Therefore, l-carnitine supplementation is unlikely to have any significant effect on muscle carnitine storage in plant based people.
Even if it did have some effect on muscle stores, it would still be unlikely to affect muscle function and energy metabolism.
Carnitine & Health Outcomes
Outside of sports and exercise performance, there are some potential applications for carnitine supplementation.
Aging: A meta-analysis suggests that supplementation with acetyl-L-carnitine may improve mental function and reduce deterioration in older adults experiencing cognitive impairments or alzheimers. This may be due to the importance of carnitine in mitochondrial function (13). Carnitine supplementation in these studies were between 1-3g per day.
Male infertility: Several studies indicate that carnitine supplementation may improve sperm quality (14). The carnitine content of seminal fluid is actually directly correlated with the sperm count and motility.This likely has something to do with carnitines’ role in energy production. Although a recent randomised control trial found no difference between pre and post carnitine supplementation in sperm quality (15). More research is required in this space.
Type 2 Diabetes: There is some evidence to suggest that intravenous carnitine supplementation may improve insulin sensitivity and help to regulate blood glucose levels by promptly increasing oxidation (16). One analysis has even shown a potential positive impact on nerve pain in diabetes related neuropathy (17). Although, evidence is not strong enough to make carnitine supplementation part of standardised diabetic care and the potential risks are currently unknown.
How to take carnitine
Generally, carnitine supplementation is not advised for most people including vegans and vegetarians.
In certain health conditions, carnitine supplementation may be appropriate but dosages would likely be dependent on the individual person and condition.
The research is typically done with doses of L-carnitine ranging from 1-6g per day.
Risks of carnitine supplementation
Carnitine supplementation does come with some potential risks.
At doses of 3g or more, carnitine supplementation may cause nausea, vomiting, abdominal cramps, loose bowel movements and a fishy body odour (18).
What is more concerning is the research regarding l-carnitine and a possible increase in risk of cardiovascular disease. Research is still emerging but l-carnitine may play a role in the advancement of atherosclerosis.
The proposed mechanism is that l-carnitine is metabolised by intestinal gut bacteria to form a substance called trimethylamine N-oxide (TMAO). TMAO has been linked with an increased risk of heart disease but the implications of supplementation or a high dietary intake of carnitine are not well understood (19).
Closing thoughts
Carnitine supplementation is unlikely to be beneficial for any healthy person, even when it comes to athletic performance.
Deficiency can occur if there is an inadequate intake of protein, vitamin C, iron, B3 or B6 but this isn’t isolated to vegans and vegetarians.
Although a lower intake of protein and iron can be more prominent in plant based people.
Even though vegans and vegetarians do not consume much dietary carnitine, they can simply rely on endogenous carnitine production and skip the supplementation.
Just ensure that your general diet is adequate in protein, iron, vitamin C and B-vitamins so that the carnitine production process has all of its necessary ingredients.
This article was written by Plant Nutrition and Wellness’s resident plant based sports dietitian and nutritionist Leah Higl. If you’re following a plant-based or vegan diet and want to make sure you’re meeting all your nutritional needs, optimise your performance and have an individualised nutrition plan created uniquely for you, get in touch today.
References
- National Institute of Health – Carnitine
- Carnitine status of lactoovovegetarians and strict vegetarian adults and children
- Effect of L-carnitine supplementation on the body carnitine pool, skeletal muscle energy metabolism and physical performance in male vegetarians
- Changing to a vegetarian diet reduces the body creatine pool in omnivorous women, but appears not to affect carnitine and carnosine homeostasis: a randomised trial
- L-carnitine supplementation for the treatment of fatigue and depressed mood in cancer patients with carnitine deficiency: a preliminary analysis
- Acetyl-L-carnitine for the treatment of HIV lipoatrophy
- Carnitine replacement in end-stage renal disease and hemodialysis
- Role of carnitine in disease
- Iron status of vegans and vegetarians
- The role of carnitine and carnitine supplementation during exercise in man and in individuals with special needs
- Supplemental carnitine and exercise
- Carnitine and sports medicine: use or abuse?
- Meta-analysis of double blind randomized controlled clinical trials of acetyl-L-carnitine versus placebo in the treatment of mild cognitive impairment and mild Alzheimer’s disease
- L-carnitine levels in the seminal plasma of fertile and infertile men: correlation with sperm quality
- Carnitine for the treatment of idiopathic asthenospermia: a randomized, double-blind, placebo-controlled trial
- L-carnitine improves glucose disposal in type 2 diabetic patients
- Acetyl-L-carnitine improves pain, nerve regeneration, and vibratory perception in patients with chronic diabetic neuropathy: an analysis of two randomized placebo-controlled trials
- Carnitine: Lessons from one hundred years of research
- l-Carnitine in omnivorous diets induces an atherogenic gut microbial pathway in humans
