Is it time to add dietary fish to the list of potential causes of coronary heart and kidney disease based on new research findings (http://www.ncbi.nlm.nih.gov/pubmed/27377678)? Tri-methyl amine oxide or TMAO is a newly described compound that our bodies produce and that has created a whole new field of understanding the diet-heart and the diet-kidney hypothesis. TMAO is produced by intestinal bacteria as a result of our dietary choices and the composition of our gut bacteria or microbiome. Work at the Cleveland Clinic has shown that TMAO increased the accumulation of cholesterol in the wall of arteries to begin plaque buildup (http://www.ncbi.nlm.nih.gov/pubmed/23563705). The researchers also demonstrated that it was the bacteria in the GI tract that were producing TMAO (http://www.ncbi.nlm.nih.gov/pubmed/23563705). Finally, TMAO has been shown to be associated with chronic kidney disease (http://www.ncbi.nlm.nih.gov/pubmed/26751065).
Until now, the focus on dietary sources of TMAO production has been mainly on foods rich in choline and l-carnitine such as eggs and red meat (http://www.ncbi.nlm.nih.gov/pubmed/24944063). In fact, large research studies have recently identified an association between dietary phosphatidylcholine intake (think eggs, liver and pork) with both Type 2 diabetes (http://care.diabetesjournals.org/content/38/2/e13) and all-cause and cardiovascular mortality (http://www.ncbi.nlm.nih.gov/pubmed/27281307).
What's brand-new in TMAO research that may guide our health and dietary choices? In a study involving feeding 40 healthy men various meals, fish meals yielded the highest circulating TMAO levels with a rise that was 46-62 times baseline (http://www.ncbi.nlm.nih.gov/pubmed/27377678). The rise in TMAO was higher following fish than beef, eggs or the fruit control. The rise in TMAO began only 15 minutes after eating a meal of fish. A study of the composition of the microbiome in subjects demonstrating a rapid rise in TMAO levels indicated that they had a different pattern of gut bacteria than those that did not show a bump in the blood levels of TMAO (i.e more Firmicutes was found).
A remedy for the production of TMAO other than avoidance of foods, largely animal based, that are high in the substrates for TMAO, is unclear. To date, no probiotic has been shown to halt TMAO production. An inhibitor of TMAO production, DMB, has been described in animal studies but the safety and efficacy in humans will need further study (http://www.ncbi.nlm.nih.gov/pubmed/26699388).
For now, avoiding or limiting dairy, eggs, meat and fish may be a wise path to prevent or halt heart and kidney diseases. A blood test for TMAO levels is available to predict cardiovascular risk and I have seen many of my patients with sky high TMAO levels return to normal after reducing or eliminating sources of animal foods as well as supplements with L-carnitine and choline derivatives. While we have much to learn about TMAO and health, the rapidly growing scientific database, now in the hundreds of studies, suggests that a whole-food plant predominant or exclusive diet is a heart and kidney smart choice.