Role of Gut Microbes in Preventing Disease

By Dr. Paul E. Lemanski, MD, MS, FACP

Medicines are a mainstay of American life and the healthcare system, not only because they are perceived to work by the individuals taking them, but also because their benefit may be shown by the objective assessment of scientific study. Clinical research trials have shown that some of the medicines of Western science may reduce the risk of heart attacks, strokes and cardiovascular death, while others may reduce certain types of cancer.

In the first 79 installments of the Non-Medicated Life, informed diet and lifestyle have been shown to accomplish naturally for the majority of individuals most of the benefits of medications in the treatment of chronic medical conditions – such as hypertension, high cholesterol, diabetes and heart disease. Emerging research suggests that the non-medicated approach to maintaining health and preventing diseases may also depend on the types of microorganisms that inhabit our gut.

Our gut is home to trillions of bacteria – the gut microbiome – that up to the last several years were not suspected of playing a role in diseases, apart from certain infectious diarrheas. More recently, however, the gut microbiome composition has been associated with disease states including obesity, diabetes, inflammatory bowel disease, cancer, and even cardiovascular disease.

This association does not only imply harm in being colonized by gut pathological species. The gut microbiome also provides established benefit, including protection from the invasion of such pathogens. For example, the probiotic use of yogurt containing lactobacillus species concomitant with the use antibiotics, helps avoids diarrhea caused by the overgrowth of intestinal pathogens.

Beneficial bacteria alter the acid base balance of the small intestine, and produce volatile fatty acids that kill pathogenic bacteria. Benefits also include regulation of gut motility, the production of vitamins, enhanced absorption of minerals, and the destruction of toxins and substances, which can cause mutations of host DNA. The gut microbiome transforms the lignans in foods such as flaxseed, cruciferous vegetables and strawberries into enterolignans, the biologically active compounds that may reduce the risk of cardiovascular disease – as well as hormone sensitive cancers such as breast and prostate cancer.

The gut microbiome plays an important role in the metabolism of the isoflavones (contained in soy products) into active metabolites, which provide a plant-based modulation of estrogen stimulation, that may both reduce menopausal symptoms and breast cancer risk.

Additionally, growing evidence suggests that obesity may be, in part, due to a reduction in the diversity of the species making up the gut microbiome. Obese individuals have up to 40% less diversity in the gut microbiome. This may, in turn, lead to alterations in the absorption of food that could affect weight. Studies in mice suggest that transferring the gut microbes from obese mice into lean mice causes the lean to gain weight. Conversely, transferring gut microbes from lean mice to obese mice causes the obese mice to lose weight.

Probably the most interesting association between the gut microbiome and disease involves cardiovascular disease. It is well established that saturated fat and cholesterol in meat contributes to elevated serum cholesterol, which is the first condition required for the deposition of that cholesterol into the walls of arteries in the body. This deposition involves the formation of a cholesterol plaque in the wall of an artery, in a process called atherosclerosis. This deposition is the underlying condition responsible for heart attacks and strokes.

Improving the ability to predict if an individual with high cholesterol will have a heart attack or stroke has led medical researchers to look for additional ways to determine or stratify risk. Recently, a substance called trimethylamine-N oxide or TMAO has been found, which increases risk for heart attacks and strokes – probably by damaging the endothelial cells that line the arteries. Importantly, the gut microbiome is involved in its production.

Moreover, in a study of patients with heart disease, those having the highest levels of TMAO had a 250% increased risk of heart attack, stroke or death – compared to those with lower TMAO levels. Most significantly, this difference was independent of the traditional cardiovascular risk factors.

In an unfortunate one-two punch, the meat or animal products we consume do not just contain saturated fat and cholesterol, which could contribute to cardiovascular disease. They also contain choline and phosphatidyl choline, both substances that the gut microbiome, under the proper conditions may convert to TMAO.

Studies of the microbiome of vegans and omnivores suggest that the bacteria in your gut are determined by what you eat. Individuals who eat meat and meat products have a gut microbiome that produces large amounts of TMAO. Individuals who eat a plant-based diet such as vegans produce almost no TMAO. While this suggests that to reduce cardiovascular risk maximally you need to be a vegan, this may not be rigorously true.

In a study of vegans and omnivores fed a meat meal, the vegans produced no TMAO and the omnivores produced large amounts, suggesting that the gut microbiome of those consistently on a plant-based diet could tolerate smaller portions of meat eaten less frequently, without an adverse impact on cardiovascular risk.

The question then becomes how to create such a plant-based microbiome. Taking probiotics, while a reasonable first step, cannot encourage the appropriate diversity that is the hallmark of a healthy microbiome. Certainly the consumption of a plant-based diet is an important step. Simply eat more vegetables.

But additionally, there is evidence that not all vegetables are equally effective in the feeding and cultivation of a healthy gut microbiome. Gut bacteria need the fiber including the type of fiber folks tend to avoid, that found in the hard to chew ends of asparagus or in the stalks of broccoli. The gut microbiome needs a prebiotic fiber called fructans and the consumption of fructan-rich foods should be a priority.

Fructan rich foods include leeks, Jerusalem artichokes, white onions, legumes, artichokes, asparagus, whole grains, and fruits such nectarines and raspberries. Obviously the increase in fiber from these sources should be gradual to avoid excess gas and bloating. In conjunction with this increase in fructans, you should decrease not only the amount of meat, cheese, eggs and animal products, but also the frequency of consumption.

In summary, the gut microbiome is associated with multiple diseases and their prevention. Creation of a healthy gut microbiome may include the use of probiotics, but also the consumption of prebiotic fiber, especially that contained in fructan-rich foods. Consuming such foods as part of a predominately plant-based diet may allow the consumption of reduced portions of meat at a reduced frequency, and still ensure optimal health. As such, the cultivation of a healthy gut microbiome is an essential part of the non-medicated life.

Paul E. Lemanski, MD, MS, FACP (plemanski@capcare.com) is a board certified internist at Center for Preventive Medicine, CapitalCare Medical Group in Albany. He is medical director of the Department of Community Medicine and Population Health at CapitalCare Medical Group. Paul has a master’s degree in human nutrition. He is an assistant clinical professor of medicine at Albany Medical College, and a fellow of the American College of Physicians.