Background: Gut Bacteria eat what we eat!
The metabolism of food products by our gut bacteria, also known as the gut microbiome, produce metabolites that have effects on our health. When exposed to the foods we eat, the bacteria in our gut are faced with the task of digesting and metabolizing it too. Substances are produced as a byproduct of this metabolism that affect us. We are still learning what role these substances play in health, but two such substances we will discuss today are short chain fatty acids (SCFAs) and TMAO (trimethylamine N-oxide).
Short Chain Fatty Acids
The role of short chain fatty acids or SCFAs is being studied extensively and thus far, appear to be a key player in how the gut microbiome affects our metabolic health.
SCFAs (Acetate, propionate and butyrate are primary products) are produced from the fermentation of dietary fiber by bacteria. SFCAs and their actions lead to various effects in the intestines, as well as in the blood supply of the gut and the rest of the body.
SFCAs appear to decrease risk for type 2 diabetes, decrease risk for obesity and also affect appetite regulation.
They affect gut barrier function and affect glucose/carbohydrate handling (insulin sensitivity and production of glucose by the body) which in turn appears to decrease the risk for type 2 diabetes. Processes such as use and storage of fat also appear to be affected, which affects obesity risk. Additionally, there are effects on appetite regulation with acetate, propionate and butyrate having an appetite suppressive effect in the brain and by helping to increase fullness. Effects on immune system function and risk for cardiovascular disease (CVD) are also seen.
It appears SFCAs have a beneficial effect on heart and metabolic health as they:
— Decrease in diastolic blood pressure
— Decrease in inflammation
— Prevent translocation of gut bacteria along the lining of the gut and therefore reducing leaky gut/inflammation
Other substances produced by metabolism of other dietary factors by gut bacteria are also being studied as to their effects on metabolic health.
One such substance is TMAO. Gut bacteria produce trimethylamine, a by-product of choline and carnitine metabolism- choline is a nutrient found not only in red meat, but also eggs, fish, and poultry. Carnitine is mainly found in red meat. Subsequently, the liver converts trimethylamine to trimethylamine N-oxide (TMAO). TMAO appears to be a strong microbiome-mediated risk factor for CVD.
A JAMA article in June, 2019 looked at 3 analyses of TMAO and the effect on CVD risk.
In one of those studies, people with higher levels of TMAO in their blood were found to have more than twice the risk of heart attack, stroke, or other serious cardiovascular problems, compared with people who have lower levels.
In a review of literature on TMAO in 2017, it appears high TMAO levels are associated with the development of insulin resistance (increased risk for type 2 diabetes), gastrointestinal cancers (Ex. stomach/colon cancer) and cardiovascular disease (Ex. heart attack, stroke).
The mechanism of red meat contributing to heart disease has been believed to be related to saturated fat. We are now learning that there is more to the story and future studies on substances like TMAO, how to reduce them, and what probiotics we can use to lower their production, will help guide future nutritional and therapeutic recommendations.
While studies help define the roles these substances play in metabolism, in the meantime, we do know one thing: a diet with more plant-based foods and fiber can help to decrease TMAO levels in the body, as well as increase the production of SFCAs as described above. So, even if you are not eliminating all animal products, reducing the amount of them, and opting for more plant-based fiber can be a great start towards helping your gut microbiome work for your metabolism and health!
Richa Mittal, MD
Disclaimer: Please note this information is for educational purposes and is not medical advice. Please consult with your own personal physician for any health concerns.
Chambers ES, Preston T, Frost G, Morrison DJ. Role of Gut Microbiota-Generated Short-Chain Fatty Acids in Metabolic and Cardiovascular Health. Curr Nutr Rep. 2018;7(4):198–206. doi:10.1007/s13668-018-0248-8
Abbasi J. TMAO and Heart Disease: The New Red Meat Risk? JAMA. 2019;321(22):2149–2151.
Jens Oellgaard*, Signe Abitz Winther, Tobias Schmidt Hansen, Peter Rossing and Bernt Johan von Scholten, “Trimethylamine N-oxide (TMAO) as a New Potential Therapeutic Target for Insulin Resistance and Cancer”, Current Pharmaceutical Design (2017) 23: 3699. https://doi.org/10.2174/1381612823666170622095324