Carnitine

Carnitine plays a key role in lipid metabolism as a carrier of fatty acids and acetate across the mitochondrial membrane. Primary dietary sources include red meat and dairy products. In addition to its role in normal metabolism, therapy with carnitine has shown promise in treating selected patients with altered carnitine homeostasis where it appeared to improve cardiac function, increase exercise capacity, and reduce muscle cramps.

In normal individuals, early research on supplemental L-carnitine's effect on endurance performance yielded conflicting results. However, more recent investigations, have suggested a beneficial effect of supplemental L-carnitine in training, competition, and recovery from strenuous exercise.

Early articles indicated a lack of toxic side effects and concluded that as a supplement it could be taken with impunity. But it now appears that although carnitine itself is not toxic, a product of its metabolism by bacteria in the colon (the microbiome) may be a key factor in the development of atherosclerosis. These conclusions are supported by this meta-analysis demonstrating a positive dose-dependent association between TMAO plasma levels and increased cardiovascular risk and mortality.

We know that the composition of a person's microbiome is influenced by diet. Provide more of any specific food in the diet and the bacteria that thrive on it multiply in the colon. Interestingly, production of TMAO from creatine supplements is minimal in vegans compared to those on unrestricted diets. Presumably their diets, low in carnitine, have limited the number of specific meat (and carnitine) metabolizing bacteria in their colons.

Should you consider using carnitine as a performance supplement? For the recreational rider, the health risks of regular carnitine supplements would seem to outweigh any performance benefits and I'd say no. For the competitive athlete looking for even a slight performance edge, the use of a loading dose pre-event (but not in training i.e. on a regular basis) should minimize exposure to TMAO (and its cardiovascular risks). That is a decision each athlete will have to make for themselves.

Picking your proteins - the health implications of TMAO

Excessive carbohydrate calories, especially from the simple sugars glucose and fructose, increase the risk for obesity, high blood pressure, heart disease, and even cancer. This is less of a concern when these simple sugars are being used to replace Calories expended by the training or competing athlete. But for the occasional recreational rider, cutting back on carbohydrates is a healthy choice. However that will mean increasing the fat and protein calories in your diet. But what kind of fat? And what kind of protein?

Cholesterol and saturated fats have been tagged as major risk factors for blood vessel disease (atherosclerosis) for decades. But recent work suggests they are not the most important factor in all those heart attacks. Merely a late stage contributor to damage already well under way.

The results of numerous studies and investigations points to Trimethylamine N-Oxide (TMAO) as the real culprit.

There is proof of cause and effect. In an experimental mouse model, raising blood TMAO levels by dietary manipulation increased blood vessel disease in the absence of any changes in the cholesterol or fat content.

Numerous clinical studies of heart disease (chest pain in the ER, progression of known atherosclerotic heart disease) show a direct correlation between increasing blood levels of TMAO and cardiovascular disease.

Carnitine, a protein found in red meat and to a much lesser degree in chicken and fish, is the source of TMAO. Any dietary carnitine not digested and absorbed in the small bowel passes into the colon where bacteria (our microbiome) metabolize it to an intermediate molecule, TMA. TMA is in then absorbed and modified further in the liver to TMAO.

There is a similar pathway for the production of TMAO from lecithin, a protein found in eggs.

Solid evidence supports diet as the major determinant of blood TMAO levels. A recent study documented a diet low in red meat and eggs lowered TMAO levels independent of the amount of cholesterol or saturated fats in those diets.

TMAO production can be reduced with oral antibiotics (which alter the makeup of the microbiome) or by decreasing the dietary intake of carnitine. Vegans as a group have the lowest blood TMAO levels (and the lowest rate of cardiovascular diseases) while those on a regular red meat diet the highest. just replacing red meat with chicken will lower the amount of TMAO excreted in the urine by two thirds.

What does this suggest for your diet?

1. The current emphasis on limiting dietary carbohydrates means caloric requirements will be replaced by increasing amounts of protein and fat.
2. Saturated fats, found in butter, cheese, red meat and other animal-based fats play a role in cardiovascular disease, but their risk may be less than once thought (and less than excess carbohydrates).
3. Your decision on protein will then take on more importance in your long term health. We know that vegetarians have the lowest levels of blood vessel disease, and your goal should be a move toward a meat free, plant based protein diet. But that does not mean you have to become a total vegetarian. Any decrease in red meat will be a plus. Add one or two meat free dinners a week, decrease red meat portion sizes, or substitute chicken or fish as the meat course. Plant based protein alternatives remain at the top of my list.