By: Jennifer Sarrett & Amanda Freeman

Tomorrow is the Atlanta March for Science. This event is aimed to bring people together to push for more publicly funded and disseminated science. Attendees are in support of the positive role science has in our lives and are against discrediting scientific findings. Further, the March for Science organizers have stated in their mission the need for more scientists to be involved in policy and politics. Specifically, they state:

“The best way to ensure science will influence policy is to encourage people to appreciate and engage with science. That can only happen through education, communication, and ties of mutual respect between scientists and their communities — the paths of communication must go both ways. There has too long been a divide between the scientific community and the public.”

The March starts at 10 am in Historic Old Fourth Ward Park and ends in Piedmont Park at the Atlanta Science Festival. As we do each year, The Center for the Study of Human Health is hosting a booth at the Atlanta Science Festival!

The booth is titled: “Your 100 Trillion Best Friends” and can be found at Booth E621 at the 2019 Atlanta Science Festival Exploration Expo. This year’s Festival Team includes Anika Sharma, Janis Choi, Mallika Kolachala, Medha Alavalapati, and Mo Singhal. This year’s booth topic is gut microbes.

It is important that the microbial population in a mammal’s gastrointestinal tract maintains a high level of diversity. These gut microbes play a crucial role metabolism, protecting us against pathogens, and developing our immune system. Recent evidence suggests that these organisms, which are too tiny to see, have a large impact on the human host’s health in areas such as development, fertility, lifespan, and behavior.[1]

Our bodies are comprised of different landscapes, some moist and others oily or dry, and microbial species only thrive in certain environments. These microbiological landscapes across our body play a key role in the mechanisms which maintain our health.[2] For example, the microbes in our mouth are very different (and serve a very different purpose) from the microbes on the bottom of our feet. In fact, have you ever wondered why feet tend to smell bad? After counting and mapping bacterial populations that reside on the foot, one study found that variations in the microbes were responsible for the localized production of odor across the foot.[3]

The vibrant community of microbial life across specific locations of our body can significantly influence our overall health. Since the human gut is home to an estimated 10 trillion microbes,[4] it is a critical site for human interaction with the microbial environment [5]. The gut microbiome helps keep the body’s immune system in check by building our tolerance to unfamiliar, but non-pathogenic microbes.[5] In addition, the competition for space and nutrients among microbes living in our gut helps keep disease-causing bacteria from moving in and taking over the gut.[6] Microbial diversity has also been linked to a strong gut barrier, which is more effective in keeping the millions of bacteria that inhabit our guts, out of the body’s bloodstream where they can cause disease.[6, 7] Therefore, diversity is key for a healthy microbiome.

The food we eat helps shape the diversity of our gut microbiome.[8] Microbes aid in breaking down and processing carbohydrates, but they also need enough energy to function properly.[9] The composition of gut microbes is dependent upon what we eat and high fat and high sugar foods, like donuts, funnel cake, and cinnamon buns, don’t provide the necessary nutrients to support a wide range of microbes. The composition of gut microbes responds quickly to changes in the nutrients we provide through our diet. For example, switching between a plant-based diet and an animal-based diet can change the microbial community of the gut within days.[10] Plant-based foods contain an abundance of fiber which helps increase populations of Ruminococcaceae and Lachnospiraceae, which help sustain the growth of the cells in our gut.[11] Since gut microbes must survive on what we eat, it is important to have a diverse diet, including plenty of fruits and vegetables and reasonable amounts of lean proteins, to support a diverse gut microbiome.[8]

Although diet is the most influential characteristic in determining the microbiome, there are several other factors that can affect microbe composition and prevalence. First, birth mode plays a significant role during the first three years of life.[12] Babies born vaginally have microbiomes that contain microbes typically found in the birth canal and fecal flora whereas babies delivered by Caesarean section (C-section) have microbiomes with decreased diversity that resemble skin microbes.[13] Researchers have found an association between the low diversity found in C-section babies and increased risks of autoimmune diseases, such as asthma,[14] Celiac’s disease,[15] and obesity.[16] Further, components of the mother’s microbiome, including antibodies, are passed down to the baby through breast milk.[17]

Another notable factor is environment, which, through twin studies, has been found to be more important in shaping the microbiome than genetics.[18] In fact, only two to eight percent of the human microbiome is passed on through genes.[19] In terms of environment, those living in rural areas are found to have more diverse microbiomes than those in urban areas.[20] As mentioned earlier, diversity is key, so making an effort to go outside and get some fresh air is one way to improve your microbiome!

Finally, age has been linked to changes in microbiome composition. Older people typically have less diverse microbiomes as well as increased frequency of inflammatory microbes.[21] However, a 2017 study found that “ridiculously healthy” elderly people have microbiomes that are similar to those of healthy 30-year-olds.[22] Just as with environment, studies like this demonstrate that we may have increased control over our microbiome, and by association, overall health.

While many think of microbes as harmful to our health, the majority are necessary for health as described above. However, bacteria can occasionally make us sick enough to require treatment. Antibiotics may be necessary to eliminate these disease causing bacteria, but they simultaneously eliminate beneficial bacteria too. Responsible use of antibiotics only when necessary can help maintain the diversity of our microbiome.

References:

1. Gould, A.L., et al., Microbiome interactions shape host fitness. Proc Natl Acad Sci U S A, 2018. 115(51): p. E11951-E11960.

2. Bell, J.S., et al., Invited Review: From nose to gut – the role of the microbiome in neurological disease. Neuropathol Appl Neurobiol, 2018.

3. Stevens, D., et al., Spatial variations in the microbial community structure and diversity of the human foot is associated with the production of odorous volatiles. FEMS Microbiol Ecol, 2015. 91(1): p. 1-11.

4. Arumugam, M., et al., Enterotypes of the human gut microbiome. Nature, 2011. 473(7346): p. 174-80.

5. Eckburg, P.B., et al., Diversity of the human intestinal microbial flora. Science, 2005. 308(5728): p. 1635-8.

6. Leslie, J.L., et al., The Gut Microbiota Is Associated with Clearance of Clostridium difficile Infection Independent of Adaptive Immunity. mSphere, 2019. 4(1).

7. d’Ettorre, G., et al., Probiotic supplementation promotes a reduction in T-cell activation, an increase in Th17 frequencies, and a recovery of intestinal epithelium integrity and mitochondrial morphology in ART-treated HIV-1-positive patients. Immun Inflamm Dis, 2017. 5(3): p. 244-260.

8. Pace, L.A. and S.E. Crowe, Complex Relationships Between Food, Diet, and the Microbiome. Gastroenterol Clin North Am, 2016. 45(2): p. 253-65.

9. Wong, J.M., et al., Colonic health: fermentation and short chain fatty acids. J Clin Gastroenterol, 2006. 40(3): p. 235-43.

10. David, L.A., et al., Diet rapidly and reproducibly alters the human gut microbiome. Nature, 2014. 505(7484): p. 559-63.

11. Parkar, S.G., A. Kalsbeek, and J.F. Cheeseman, Potential Role for the Gut Microbiota in Modulating Host Circadian Rhythms and Metabolic Health. Microorganisms, 2019. 7(2).

12. Yatsunenko, T., et al., Human gut microbiome viewed across age and geography. Nature, 2012. 486(7402): p. 222-7.

13. Dominguez-Bello, M.G., et al., Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns. Proc Natl Acad Sci U S A, 2010. 107(26): p. 11971-5.

14. Kero, J., et al., Mode of delivery and asthma — is there a connection? Pediatr Res, 2002. 52(1): p. 6-11.

15. Decker, E., et al., Cesarean delivery is associated with celiac disease but not inflammatory bowel disease in children. Pediatrics, 2010. 125(6): p. e1433-40.

16. Mueller, N.T., et al., Prenatal exposure to antibiotics, cesarean section and risk of childhood obesity. Int J Obes (Lond), 2015. 39(4): p. 665-70.

17. Mueller, N.T., et al., The infant microbiome development: mom matters. Trends Mol Med, 2015. 21(2): p. 109-17.

18. Goodrich, J.K., et al., Genetic Determinants of the Gut Microbiome in UK Twins. Cell Host Microbe, 2016. 19(5): p. 731-43.

19. Rothschild, D., et al., Environment dominates over host genetics in shaping human gut microbiota. Nature, 2018. 555(7695): p. 210-215.

20. Parajuli, A., et al., Urbanization Reduces Transfer of Diverse Environmental Microbiota Indoors. Front Microbiol, 2018. 9: p. 84.

21. Choi, J., T.Y. Hur, and Y. Hong, Influence of Altered Gut Microbiota Composition on Aging and Aging-Related Diseases. J Lifestyle Med, 2018. 8(1): p. 1-7.

22. Bian, G., et al., The Gut Microbiota of Healthy Aged Chinese Is Similar to That of the Healthy Young. mSphere, 2017. 2(5).

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