Dietary patterns have long been recognized as a critical component of our health and are also known to play a prominent role in the composition of the gut microbiome. For instance, research has shown that changing from an animal-based diet to a plant-based diet results in astonishingly rapid changes in the gut microbiome. Research has just begun skimming the surface of the mechanisms behind which foods help and harm the health of the gut microbiome. This is an important area of investigation because the gut microbiome is believed to play a pivotal role in our overall health – including our skin health.
The trillions of different microbes that live in our small and large intestines influence our health by helping to digest the food we eat, protect against disease causing infections, and even make vitamins. It turns out, there is a compound called L-carnitine present in many foods that is converted by our gut microbes to a chemical that may be linked to increased risk for heart attack and strokes.
What Is L-Carnitine?
L-carnitine (or carnitine) is a type of amino acid (the molecules that make up the building blocks of proteins) found normally in most cells throughout the body. Our bodies naturally produce enough carnitine to carry out its functions in energy production and detoxification. When we ingest food that contains L-carnitine, the resident bacteria in our gut break it down to produce a different chemical called trimethylamine (TMA). TMA is then converted to trimethylamine N-oxide (TMAO) by our liver. In a study at the Cleveland Clinic, researchers found that TMAO produced as a result of gut bacteria metabolism is associated with plaque buildup in arteries throughout the body (a disease called atherosclerosis). In this study, meat-eaters had had a higher prevalence of Prevotella microorganisms, which the researchers hypothesized to contribute to their higher levels of TMAO. On the other hand, the vegan and vegetarian individuals had a higher predominance of Bacteroides species and much lower TMAO levels. In fact, in a study of over 2,000 humans, higher blood levels of TMAO were even associated with premature death. This research highlights the influence the gut microbiome may have over the health of our blood vessels and our ultimate longevity.
L-carnitine is present primarily in meat. Red meat of all kinds (processed and unprocessed) contain L-carnitine, including beef, lamb, pork, and veal.
Many energy drinks are formulated with L-carnitine, probably due to its known role in energy metabolism. Look carefully at nutrition labels on beverages to look for how much L-carnitine it may contain.
Dairy products, specifically within the whey protein, contain L-carnitine, but in lesser amounts compared to red meat.
Table 1. Examples of carnitine content in select foods
Carnitine Content (milligrams)
4 ounces beef steak
4 ounces ground beef
1 cup whole milk
4 ounces chicken breast
4 ounces ice cream
0.1 mg (per slice)
½ cup cooked asparagus
Source: Adapted from Modern Nutrition in Health and Disease
The Bottom Line
Altogether, this research poses the significant impact that diet has on our health and the importance of creating a healthy gut microbiome. There appears to be a significant link between elevated TMAO levels in our blood and increased risk for blood clot-related events, such as stokes and heart attacks. These intriguing results demonstrate how we could potentially lower our risk for blood vessel disease simply by reducing foods and supplements in our diets that contain L-carnitine. In fact, vegetarians and vegans have been shown to have significantly reduced TMAO levels compared to meat-eaters. Eating a diet rich in plant based foods and fiber may be beneficial to our gut microbiome and our overall health.
Although it is uncertain whether TMAO levels contribute to skin conditions, it is important to understand that gut bacteria can metabolize many other compounds we consume in our diet. For instance, consuming high fiber foods can result in gut bacteria production of short chain fatty acids, such as butyrate and propionate. There is evidence that production of these compounds can induce the immune system to fight inflammation in certain skin diseases. This highlights the importance of diet in modulating the gut microbiome to affect the skin.
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Rebouche CJ. Carnitine. In: Shils ME, Olson JA, Shike M, et al., eds. Modern Nutrition in Health and DIsease. 9 ed. New York: Lippincott Williams and Wilkins; 1999:505-512.
Koeth RA, Wang Z, Levison BS, et al. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med.2013;19(5):576-585; PMID: 23563705 Link to research.
Senthong V, Wang Z, Li XS, et al. Intestinal Microbiota-Generated Metabolite Trimethylamine-N-Oxide and 5-Year Mortality Risk in Stable Coronary Artery Disease: The Contributory Role of Intestinal Microbiota in a COURAGE-Like Patient Cohort. J Am Heart Assoc.2016;5(6)PMID: 27287696 Link to research.
Rebouche CJ. Kinetics, pharmacokinetics, and regulation of L-carnitine and acetyl-L-carnitine metabolism. Ann N Y Acad Sci.2004;1033:30-41; PMID: 15591001 Link to research.