The trillions of microbes living in your gut are your partners in health and wellness. A rapidly expanding body of research is shedding light on just how profoundly influential these microorganisms are on the human body.
Some research is showing an association between certain chronic health conditions and a disturbance in the microorganisms in the gut. It's unclear, however, if an altered gut microbiota is the root cause of the health condition or if the health condition is leading to alterations in the microbiota.
Researchers around the world and at Mayo Clinic Individualized Medicine Microbiome Program are seeking to understand how the microbiome promotes wellness and enables disease, and how that knowledge can one day change the practice of medicine. Here is a sampling of research that is exploring the microorganisms inhabiting the body and their connections to health and disease.
The Microbiome and Cancer
Scientists have learned that an individual's gut microbiome can speed up or slow down the development of cancer and influence the response to cancer treatment.1
Some of what is known is limited to mice studies. For example, research indicates that the makeup of the gut microbiome of mice impacts the size and number of liver cancer tumors.2
But important insights are leading to a better understanding of cancer in humans. An individual's microbiome can influence both the effectiveness of different cancer therapies, as well as their associated side effects. Certain types of immunotherapy – a cancer treatment that helps the immune system fight cancer – work best when patients have highly diverse communities of gut microbes.1
Researchers are also making important discoveries between the body's microbes and various cancers. One primary example is a Mayo Clinic study that identified a microbiome marker associated with endometrial cancer.
The study found that the uterine microbiome of women who had endometrial cancer is different from the uterine microbiome of women who don’t have endometrial cancer. In addition, the microbes present in the vaginal environment of women with endometrial cancer are different from the microbes present in the vaginal environment of women who don’t have endometrial cancer.3
It's not known, however, if these bacteria also cause cancer. In other words, it's not clear if the microbes were present before the cancer developed or if the vaginal microbial content changed as a result of the cancer. If aspects of the microbiome are found to play a role in causing endometrial cancer, it could have important implications for treating or preventing the disease.
Much research is underway that is exploring the relationship between cancer and the human microbiome. Manipulating this intricate ecosystem could one day help prevent or treat cancer and transform patient care. At this time, there are no proven ways to manipulate or change the microbes in the gut to improve cancer care.
The Gut Microbiome and Blood Sugar Levels
The gut microbiome might be a tool to predict how an individual's blood glucose (sugar) changes in response to eating specific foods. Glucose is the body's main source of energy. The body can make glucose and it comes from the food you eat. Elevated blood glucose levels are linked with a higher risk of developing health conditions and metabolic diseases, such as diabetes, heart disease, obesity, and kidney disease.
Studies show that an individualized diet – based on a model that accounts for age, lifestyle, and genetic differences in the microbiome – is more effective in controlling a person’s blood glucose level than a diet that only considers the calories and carbohydrates found in food.4,5
A Mayo Clinic study that followed 327 participants for six days showed that an individualized diet accurately predicted blood sugar response to food 62 percent of the time. Whereas, predictions based on carbohydrates were correct 40 percent of the time and predictions based on calories had a 32-percent accuracy rate.4
These findings shed light on why some people can eat fruit and feel energized, while others eat fruit and experience a blood sugar spike that eventually makes them feel tired. The research is based on the idea that instead of trying to change the bacteria in your gut, you might be able to adapt your diet to best suit that inherent group of bacteria.
This model is a first step in developing personalized nutritional strategies that tackle metabolic diseases. One day, it could provide physicians a new tool to improve patient health through diet, although follow-up studies are needed to assess the long-term effects of this approach.
The Gut Microbiome's Role in Rheumatoid Arthritis
One indicator of whether or not a patient with rheumatoid arthritis will improve might lie in the gut.6,7 Rheumatoid arthritis is a chronic disorder characterized by joint inflammation and pain that can eventually lead to bone and cartilage erosion, joint deformity, and loss in mobility.
A recent study by Mayo Clinic researchers found the gut microbiome is linked to an individual's future prognosis of the disease.6 Researchers used gut microbiome data and artificial intelligence to predict patient outcomes with a 90-percent accuracy rate.
The study examined two stool samples, collected 6-12 months apart, from 32 patients who had rheumatoid arthritis. Researchers discovered that patients who showed clinical improvements had different gut microbiome traits than patients whose condition did not improve.
Scientists have long suspected that the gut microbiome plays a role in rheumatoid arthritis, as well as other inflammatory and autoimmune diseases. The findings from this study indicate that gut microbes and a patient's outcome of rheumatoid arthritis are connected.
Although more research is necessary to determine the cause and effect, analyzing and modifying the gut microbiome might provide future treatment options for rheumatoid arthritis.
Mathematical Formula Determines if You and Your Gut Microbiome Are Healthy
Mayo Clinic researchers have developed a test that predicts a person’s general health status by measuring the levels of specific gut microbial species.8 Called the Gut Microbiome Health Index (GMHI), the formula does not diagnose specific diseases at this stage; rather, the GMHI distinguishes a healthy microbiome from one that is diseased and offers a general indication of an individual's health.
For the study, researchers analyzed 4,347 stool samples. Around 2,600 samples came from healthy subjects who had no diagnosed illness. The rest of the samples were from non-healthy phenotypes, such as individuals with colon cancer, diabetes, arthritis, heart disease, or obesity.
The researchers compared the frequencies of microbes within both groups. They found some microbes were more prevalent in the healthy group compared to the non-healthy group, and vice versa.
The study identified 50 specific microbial species that determine a healthy microbiome. This microbiome "signature" was validated in an independent cohort of 679 stool samples – in which the formula accurately distinguished healthy subjects from non-healthy subjects 74 percent of the time.
At this stage, the GMHI is still being developed in the lab. Researchers want to enhance its accuracy by including more disease phenotypes and a greater array of ethnic and geographical populations.
The bottom line is that poor gut health is associated with a vast range of adverse health conditions. Unraveling the cause and effect of an unhealthy gut microbiome is highly complex, and the research is constantly evolving. Providing insight into an individual's health status from a gut microbiome sample is an important clinical goal in current human microbiome research and holds promise to improve health care.
- The human microbiome in cancer. National Cancer Institute. Center for Cancer Research. https://ccr.cancer.gov/news/horizons/article/human-microbiome-in-cancer. [Accessed November 19, 2021]
- Ma C, Han M, Heinrich B, et al. Gut microbiome-mediated bile acid metabolism regulates liver cancer via NKT cells. Science 2018;360(6391):eaan5931.
- Walther-António MR, Chen J, Multinu F, et al. Potential contribution of the uterine microbiome in the development of endometrial cancer. Genome Med 2016;8(1):122.
- Mendes-Soares H, Raveh-Sadka T, Azulay S, et al. Assessment of a personalized approach to predicting postprandial glycemic responses to food among individuals without diabetes. JAMA Netw Open 2019;2(2):e188102.
- Zeevi D, Korem T, Zmora N, et al. Personalized nutrition by prediction of glycemic responses. Cell 2015;163(5):1079-1094.
- Gupta VK, Cunningham KY, Hur B, et al. Gut microbial determinants of clinically important improvement in patients with rheumatoid arthritis. Genome Med 2021;13(1):149.
- Hur B, Gupta VK, Harvey-Huang H, et al. Plasma metabolomic profiling in patients with rheumatoid arthritis identifies biochemical features predictive of quantitative disease activity. Arthritis Res Ther 2021;23(1):164.
- Gupta VK, Kim M, Bakshi U, et al. A predictive index for health status using species-level gut microbiome profiling. Nat Commun 2020;11(1):4635.