Of Bugs and Beans: Why “Plant Fed” Guts Have the Healthiest Microbiomes

The motivational speaker Charlie “Tremendous” Jones is given credit for the quote “the people you meet and the books you read” will determine your future. In terms of human health, the corollary might well be “the foods you eat and the bugs you feed” will determine your future. The term “microbiome” is creeping into public conversations of health. The microbiome refers to microorganisms, mainly bacteria, on our skin, in our fluids, and predominantly in our colon. These bacteria may make up several pounds of our body weight, occupy a mass almost as big as our liver, and have an enormous influence on our health. The potential role for health and disease that these invisible friends that live on us and in us have is so great that the National Institutes of Health has a Human Microbiome Project to explore the importance of this aspect of health and disease.

The rapid rise of chronic diseases afflicting Western societies, like coronary heart disease, type 2 diabetes mellitus, obesity, cancer and others has precipitated a rather energetic discussion over optimal dietary approaches to health and disease prevention. A robust body of clinical data suggests that a diet of plants has advantages for health and prevention of disease. In terms of the number 1 cause of death, cardiovascular disease, a diet of plants has also had widespread support in the scientific literature. Long term plant diets are associated with lower markers of inflammation. Another aspect of plant diets that may favor health is the possibility that a diet of whole foods of plant origin have a favorable impact on the human microbiome and reduced disease occurrence. Can you change your microbiome and upgrade it to a healthier mix by changing your diet to plants? In other words, can you change your bugs to change your life?

In a recent study, this question was examined formally and the results were astounding. For 2 weeks, rural South Africans were asked to change their diet to that of a US African-American western style fare much lower in fiber and higher in fat (meat and cheese). Similarly, US African-Americans adopted the “African” style diet high in fiber and low in fat, emphasizing vegetables, beans and cornmeal with little meat. Subjects agreed to a colonoscopy with biopsies along with characterization of their stool content after the 2-week diet switch. The changes were profound with the western-style diet leading to changes in blood, biopsy and microbiome analysis indicating a much higher predicted risk of colon cancer. On the traditional African diet the production of butyrate skyrocketed, a fatty acid proven to protect against colon cancer. This may explain why colon cancer in US African-Americans is more than 10 times higher than in rural South Africans. The ability to improve your microbiome in just 2 weeks of a rural diet rich in fiber from beans and other plants gives a path to reduce your risk of future colon cancer. The role of high fiber plant diets in boosting butyrate production for healthier colons has also been demonstrated in other cohorts.

What is known about the microbiome of humans eating only plants? In a recent investigation, vegans were compared to vegetarians and omnivores in terms of measures of their microbiome. Measurements in the vegan cohort indicated lower body weights and less pre-diabetes and hypertension. Analysis of stool bacteria showed changes according to diet classification. Those that ate no animal products had more of a bacteria called Bacteroides in the stool and less of another called Firmicutes. A particular strain of Bacteroides known as Prevotella was particularly frequent in the stool samples from the vegan study subjects. The authors concluded that “exposure to animal foods could favor a pro-inflammatory intestinal environment” favoring systemic inflammation and insulin resistance. Another study comparing the microbiome of vegans and omnivores similarly concluded that “the consumption of a plant-based agrarian diet is associated with health benefits”.

In a review article on the topic of the vegan diet and the microbiome, the researchers determined that the “reduced levels of inflammation may be the key feature linking the vegan gut microbiota with protective health effects”. The role of the vegan gut as a protective mechanism from cardiovascular disease is now focused on a metabolite derived largely from animal foods, trimethylamine-N-oxide (TMAO). I have written about this fascinating topic before. Blood levels of TMAO rise in omnivores after eating egg yolks and red meat but do not rise nearly as much in those following a long term vegan diet. This is due to differences in the microbiome of vegans and omnivores. TMAO causes atherosclerosis in animal models and humans and is related to kidney scarring and mortality in a host of chronic diseases, further research in the microbiome of plant diets is necessary and likely to be rewarding.

Interest in the role of the microbiome in health and disease is moving forward at a fast pace. Recent data in animals has linked the microbiome with healthy aging and other studies indicate a potential role for manipulating gut bacteria to enhance our mood. While there is much talk of fecal transplants and designer probiotics such as psychobiotics, the easiest plan for now is to load our diet up with fiber-rich plants naturally low in added fats, like the native diet of the rural South Africans.