So much is written today about our gut microbiome, yet the gut remains quite mysterious to us. I equate it with our knowledge of outer space. We gaze in the sky and see stars, galaxies, and planets. We have made great strides in space discoveries – we have sent men to the moon, rovers to Mars, and multiple satellites are continually collecting new data. We have vast knowledge about outer space, but there is so much more out there that is a mystery, unexplainable, and beyond our comprehension. So it is with the microbes in our digestive system, aka our gut microbiome. Like outer space, it seems what we don’t know about our gut microbiome is much greater than what we do know.
But what we do know is mind-blowing! For example, we know that our gut is home to over 40 trillion bacteria, viruses, fungi, and other cells. There are more than 1,000 bacteria species and 3 million unique gene sets. All of these compose the gut microbiome, and each one plays a specific role in how our body functions. We also know the bacteria are directly related to many health conditions, including irritable bowel disease, depression, schizophrenia, type 2 diabetes, cardiovascular disease, allergies, immunity, cholesterol, weight, energy production, hormone levels, inflammation, metabolism, nutrient absorption, and more.
Our gut microbiome includes bacteria, viruses, and fungi that can promote health and/or contribute to disease. Research shows that microbial diversity is key to our health, and our eating patterns and habits determine which microbes dominate in the gut. A whole food plant-based diet produces greater microbial diversity and a higher number of specific beneficial bacteria than a standard Western diet high in animal products and processed foods.
Examples from Research
Bacteroidetes are beneficial bacteria in the GI tract that release energy from fermented non-digested fiber and starch. They produce short-chain fatty acids (SCFAs), which influence many functions, including immunity, metabolism, and inflammation. Vegan diets produce a greater number of SCFAs. In contrast, Firmicutes are not so friendly. An increased ratio of Firmicutes to Bacteroidetes is correlated with type 2 diabetes and obesity because of the influence Firmicutes have on our glucose and fat metabolism. One study compared bacteria of an Indian population whose diet was predominately whole grains and plant-based vegetarian diet but did include a small number of animal protein foods to the diet of Chinese whose diet was heavier in animal protein and fat than was the diet of the Indian population. The percentage of Bacteroidetes in the Indian population was four times greater than the Chinese – 16.39% vs. 4.2%. The study concluded that a diet with few animal products was associated with a greater amount of the beneficial Bacteroidetes bacteria.[i]
Several gut bacteria, including L-Ruminococcus, are associated with the consumption of animal protein and fat. These microbes release TMA (trimethylamine), which the liver converts to TMAO (Trimethylamine N-Oxide). TMAO contributes to inflammation in the body. TMAO is also associated with cardiovascular disease and neurological disorders.[ii] Because vegetarians have different gut microbiota than people who eat a typical Western diet, vegetarians are less likely to produce TMAO. By extension, those eating a healthy whole food plant-based diet generally have less inflammation and significantly decreased risk of cardiovascular disease.
These are just two examples of how our gut bacteria and our health are influenced by what we eat. Interestingly, there is also strong evidence that exercise also affects our gut bacteria.
The University of Illinois conducted the first human study to examine the effects of exercise on the gut microbiome. Thirty-two adults took part in six weeks of endurance exercises. Prior to the study, all participants were sedentary. Eighteen participants, of which 9 were female, were lean. Fourteen participants were obese, 11 of which were female. Participants began their exercise regimen with 30 minutes of easy walking or cycling three days a week and worked their way up to 60 minutes of vigorous jogging or pedaling three times a week. They did not change their diet. At the end of the study, all stopped exercising. Fecal samples were taken before the study and again six weeks after the study concluded. All participants’ gut bacteria responded uniquely to exercise. Results showed gut bacteria did change when both the lean and obese groups exercised, but the changes were different between the two groups. Although the training was the same in both groups, the SCFAs, which help reduce inflammation and insulin resistance and boost our immune system, had a greater increase in their numbers in the lean participants than they did in the obese participants. Most of the changes in gut microbiota that occurred during exercise disappeared in all participants after they were no longer exercising.[iii] The results suggest that both the number and diversity of gut microbes respond to exercise. However, how exercise influences the gut microbiome is not fully understood.
Another study found more diversity in the microbiota of professional rugby players and an increase in more than 40 different bacteria within a specific classification of bacteria compared to lean sedentary people.[iv]
The Bottom Line: What does it all mean?
1) What we eat has a significant impact on what bacteria reside in our GI tract. Specifically, the more fiber that we eat in the form of fruits, vegetables, whole grains, nuts seeds, and legumes, the more SCFAs are produced which have numerous health benefits.
2) Exercise significantly changes the makeup of our gut microbiome.
3) The degree of the change from exercise differs between lean and obese people.
4) The changes that occur in the gut microbiome as a result of exercise are completely independent of changes in the gut microbiome that occur from our diet.
We still have a lot to learn about how diet and exercise change our gut health. Thankfully, researchers are actively studying that relationship. Once the mechanisms are understood, researchers hope that exercise and diet can be used intentionally as a treatment to improve our health. Areas of further gut health study include how to increase the diversity of our gut microbiome, improve the ratio of healthy bacteria to damaging bacteria and the number of SCFAs, and how bacteria affect metabolic diseases, gastrointestinal disorders, and colon cancer.[v]
[i] Jain, A. Li XH, ChenWN. Similarities and differences in gut microbiome composition correlate with dietary patterns of Indian and Chinese adults. AMB Express, (2018)8:104, dos: 10.1186/s13568-018-0632-1.
[ii] Tomoca,A,, Bukovski, I., Rembert, E., Yonas W., Alwarith, J. Barnard, N., Kahleova, H. The Effects of Vegetarian and Vegan Diets on Gut Microbiota. Frontiers in Nutrition. don:10.3389/fnut.2019.00047.
[iii] Allen, JM, Mailing LJ, Niemiro GM, Moore R., Cook MD, White BA, Holscher HD, Woods JA. Exercise Alters Gut Microbiota Composition and Function in Lean and Obese Humans. Med Sci Sports Exerc. 2018; 50:747-757. doi: 10.1249/MSS. 0000000000001495.
[iv]Clarke SF, Murphy EF, O’Sullivan O, et al. Exercise and associated dietary extremes impact on gut microbial diversity. Gut. 2014; 63(12):1913–20.
[v] Monda, V., Villano,I., Messina, A., Valenzano, A., Esposito, T., Moscatelli, . . . Messina, G. (2017). Exercise Modifies the Gut Microbiota with Positive Health Effects. Oxid. Med Cell Longev. doi: 10.1155/2017/3831972
