Caution against eating eggs and meat by some scientists has arisen due to their production of trimethylamine N-oxide (TMAO), a dietary compound associated with heart disease. Researchers are now revealing that the gut microbiome has an influential role in this interplay.
By Sofia Popov
Recently, reports by a Cornell study raised questions on the role of circulating TMAO in heart disease; namely, if it is the cause or simply a sign of manifestation.
TMAO naturally occurs in abundance in fish, or can be generated from other nutrients including choline (from eggs) or carnitine (from meat.) After consuming foods containing TMAO, or its dietary precursors, it is thought that gut bacteria produce the fish odor compound trimethylamine (TMA). Notably, TMAO has been used as a disease risk factor, predicting heart disease and colorectal cancer. For instance, a previous study demonstrated that women who developed colon cancer showed elevated TMAO five years prior to disease onset.
A previous study demonstrated that women who developed colon cancer showed elevated TMAO five years prior to disease onset.
Still, little is understood about the effects of animal food sources on TMAO production, absorption and release in healthy adults. Despite suggested roles of gut microbes in TMAO production, the gut microbiota composition in regards to TMAO production remains unclear. Thus, in this study, the researchers sought to figure out whether the TMAO response to animal food sources would vary amongst healthy men, and if this response would change according to their gut microbiota composition.
The team ran a crossover feeding trial, where 40 healthy young men consumed four different study meals: fish (6 ounces of cod), eggs (three whole hard boiled eggs), meat (6 ounces of beef patty) and fruit (apple sauce) as a control. They were given these meals in a random order on one particular day, separated by a one-week washout. In order to profile their gut microbiota compositions, stool samples were taken before each meal, whilst TMAO levels were measured by taking blood and urine samples (both before meals and up to six hours after.)
Men with elevated TMAO levels from eating eggs and beef, also had higher levels of firmicutes in their microbial composition, as well as a less diverse gut microbiomes overall.
The results showed men with elevated TMAO levels from eating eggs and beef, also had higher levels of firmicutes in their microbial composition, as well as a less diverse gut microbiomes overall. On the other hand, those with lower TMAO level had a higher abundance of bacteroidetes. Still, it must be noted that, on its own, firmicutes expresses genes that convert choline and carnitine to TMA, which is then processed by the body into TMAO. Meanwhile, after eating fish, the mens’ circulating TMAO was raised within 15 minutes, and at 50-fold that seen after eating eggs or meat.
After eating fish, the mens’ circulating TMAO was raised within 15 minutes, and at 50-fold that seen after eating eggs or meat.
Overall, these findings suggest that circulating TMAO is influenced by an individual’s gut microbiome, whilst raising questions on the causative role in the disease process: is it the gut microbiome, or TMAO, playing the central role? Future research will need to test the role of the gut microbiome in heart disease, as well as figuring out possible ways to reduce circulating TMAO and see if this also reduces risk of heart disease.
Clara E. Cho, Marie A. Caudill et al. Trimethylamine-N-oxide (TMAO) response to animal source foods varies among healthy young men and is influenced by their gut microbiota composition: A randomized controlled trial. Molecular Nutrition & Food Research (2016). DOI: 10.1002/mnfr.201600324