Choline and carnitine have been in the news because of new research linking gut microbes to heart disease. Researchers at the Cleveland Clinic reported that individuals with advanced heart disease had elevated blood levels of TMAO (trimethylamine oxide) produced from dietary choline and carnitine by bacteria in your lower intestines. As a nutrition scientist, I find the new research fascinating, but true to form, the news media went for the sensational headlines. The media reported that eggs (a good food source of choline) and meat (a food source of carnitine) increased the risk for heart disease. Well the science is interesting, but the headlines misrepresent the findings.
The gut microbiome is an exciting new area of medical research. Scientists have new tools to begin to study and evaluate the trillion microbes living with us in our intestines. Within the huge population of microbes, some are good friends like Lactobacillus and Bifidobacteria and some less friendly includingE. coli, B. wadsworthia, and H. pylori. The gut is like a neighborhood where all must co-exist. In a normal healthy gut, friendly bacteria outnumber the less friendly neighbors. The balance of bacteria within your microbial neighborhood reflects your life experiences including the food you choose to eat, antibiotic use, daily sanitation, stress and many other factors.
To get perspective on the TMAO story, we need to delve into the chemistry of where we get TMAO. The pathway is complicated and demonstrates why a healthy gut is important. The theory proposed by the researchers is that high levels of TMAO in the blood alter cholesterol metabolism and leads to heart disease. However the researchers admit they don’t know if elevated TMAO leads to heart disease or if heart disease leads to elevated TMAO.
The TMAO story begins with formation of trimethylamine (TMA). TMA is part of the chemical structure of many natural nutrients including the essential amino acid lysine, as well as choline (essential for brain function) and carnitine (essential for fat metabolism). If these nutrients reach the lower intestines, certain bacteria break these nutrients apart to form free TMA. Some of the TMA is absorbed and travels to the liver where it is converted to TMAO by the liver enzyme FMO (flavin monooxygenase). TMAO is released from the liver into the blood and eliminated by the kidney into the urine. That’s the normal pattern. For TMAO to increase in the blood requires at least two of these steps to be abnormal. The most likely problems are abnormal gut bacteria and reduced kidney function.
Beyond the facts that multiple abnormal steps must occur simultaneously to elevate TMAO (“a perfect storm”), there are also some basic nutrition problems with the theory. First, the pathway to TMAO begins with exposure to TMA. Well, the primary dietary source of TMA is fish and everyone recommends eating more fish for heart health. This is a serious disconnect between the new theory and accepted nutrition research.
Second, can dietary choline cause the problem? Choline is a semi-essential nutrient. We make some choline within our bodies but the amount is considered inadequate especially during periods of development or stress. The Institute of Medicine has set 450 mg of choline as the daily need for an adequate intake (AI) and less than 10% of Americans consume the AI. During pregnancy and lactation requirements may increase to above 900 mg/day. A single large egg provides about 115 mg of choline similar to a pound of spinach or 1½ cups of tofu. Further, there are dozens of research studies showing that egg consumption actually improves heart health and the American Heart Association recommends increasing egg consumption to 7 eggs per week to reduce risk for macular degeneration during aging. So the headlines suggest choline and eggs cause heart disease, yet nutrition research suggests choline intake is too low for neurological health – another disconnect between established nutrition research and the media headlines.
The story is similar for carnitine. Carnitine is essential for the body to burn fats. Generally, we produce adequate amounts of carnitine within our bodies but some individuals do not. When carnitine is low, the ability to burn fats is reduced and supplements have been shown to improve fat burning. Normal daily intake of carnitine is about 0.2 grams, but carnitine supplements up to 2 grams per day have been used for decades by cardiologist for treatment of heart disease. Athletes have also routinely supplemented carnitine to improve endurance.
The new research about gut health and host metabolism is an exciting new area of biomedical science. We’re learning that the millions of microbes who live with us in our intestines affect our health but the research is still in its infancy. For now don’t be caught up in the headlines and do the simple things to protect the health of your microbes like avoiding unnecessary antibiotics and consume vegetables and fruits to provide the soluble fibers to optimize gut health.