Silent Cecum

Crossposted from Medium: Why the environmental movement should care about your bowel movements

Fifty-seven years ago, Rachel Carson described how an American town, once a patchwork of the sounds and colors of life, had come to lose its voice. Pesticides and other contaminants, she warned, were disturbing a natural balance that had evolved over millennia. Humans were designing, synthesizing, and implementing in untold tons an arsenal of chemicals- many of which were expressly designed to be hostile to life — at a rate which most ecosystems were unable to adapt to. Rachel Carson alerted the world to a developing catastrophe; the publishing of her book catalyzed the birth of the modern environmental movement, the creation of the EPA, and the banning of DDT.

Today there is a growing awareness of another ecological catastrophe. It is playing out across a much smaller stage, but the consequences at stake are similar: the loss of immense biodiversity, the destabilization of the natural order, and the widescale compromise of human health. This collapse will not be observed in our forests or our fields, but in our feces.

In recent years, there has been a broad shift in the way that we see the bacteria that occupy our bodies — see Ed Yong’s 2016 book “I Contain Multitudes”. Rather than merely being pathogens in the making, we have come to understand that the — approximately — thirty-nine trillion bacterial cells that make up our “microbiome” serve a crucial role in digestion and are a first line of defense against colonization by harmful bacteria. There is evidence that the state of our microbiome may have a hand in disease and wellness. Besides the relatively straightforward associations with obesity and diabetes, research has indicated that there is a relationship between the microbiome and autism, depression, schizophrenia, and anxiety disorders.

The microbiome is frequently characterized as both an ecosystem — imagine your GI tract as a tiny rainforest or coral reef (Yong 2016) — and as a “forgotten organ”, one that is intimately involved in our endocrine system and shares a pathway to the brain through the microbiome-gut-brain axis. An emerging body of research indicates that the conditions of modernity are destabilizing the ecosystem in a way that is affecting its capacity to fulfill its physiological role as an organ. Much has been made of the effects that our lifestyle choices have on the structure of our microbiome — like the relatively homogenized, low-fiber diet typical of westerners — which could be imagined as a type of famine for polysaccharide hungry microbes, as well as the cataclysmic effects of a course of broad-spectrum antibiotics — best compared to those of a meteoroid strike. This revelation has inspired a cottage industry of probiotic supplements in the form of germ-loaded teas, yogurts, kombuchas, popcorns, and skincare products — most with dubious long-term benefits. The genomics startup uBiome offers kits to assess the composition of clients’ gut and vaginal microbiomes — purportedly identifying bacteria associated with IBS, Crohn’s disease, ulcerative colitis, Bacterial Vaginosis, and other conditions. While traditional healthcare providers have successfully treated disease by modulating the microbiome — most notably C diff infections by way of stool transplants — uBiome seems to straddle the territory between clinicians’ offices and the emergent biohacking movement. The company’s data driven report cards reflect a growing interest in the ability to optimize one’s health through the fine tuning of the microbiome — with diet, exercise, and the right combination of pre and probiotics.

Standing in the way of this gastrointestinal utopia is the reality that many factors that influence our microbiome lie outside of our immediate control. Many of the same classes of pesticides that Rachel Carson implicated in Silent Spring, like organophosphates (Gao et al. 2018) and organochlorides (Liu et al. 2017), have been shown to affect the microbiome in lab animals. Glyphosate (Motta et al. 2018) — the active ingredient in RoundUp — modulates the development of the microbiome in honeybees and in so doing may even play a role in Colony Collapse Disorder. Glyphosate is so pervasive in the environment, that it is frequently found in rainwater.

Although the past decade has seen a burgeoning interest in the importance of the microbiome, research into its relationship with environmental chemicals has only begun in earnest in the last 3–4 years. It may be that as pesticides and other persistent organic pollutants accumulate in our environment, the altered chemical landscape permanently shifts the established structure and compositions of our gut flora into a different equilibrium. It is unknown exactly how malleable the microbiome is or how tolerant the human body is to large changes in it. A group of hunter-gatherers — the Hadza tribe — has been shown to have very large seasonal variation in their microbiome as a result of dietary changes (Schnorr et al. 2014). What is known is that there is a cohort of bacterial species, known as “Old Friends”, that have evolved in tandem with our mammalian lineage, and that the loss of some of these species can lead to poor immunoregulation and chronic inflammatory illnesses (Rook et al. 2013).

Should you have a hard time rallying behind the plight of vaginal lactobacilli — admittedly not as charismatic a victim as bald eagles or polar bears — it would pay to remember one of the cornerstone lessons of the environmental movement: the deep interconnectedness of all things. It may well be that our continued health and resilience as a species is dependent on the preservation of the microbial diversity in our guts.

Gao, B., Chi, L., Tu, P., Bian, X., Thomas, J., Ru, H., & Lu, K. (2018). The organophosphate malathion disturbs gut microbiome development and the quorum-Sensing system. Toxicology Letters, 283, 52–57. doi:https://doi.org/10.1016/j.toxlet.2017.10.023

Liu, Q., Shao, W., Zhang, C., Xu, C., Wang, Q., Liu, H., . . . Gu, A. (2017). Organochloride pesticides modulated gut microbiota and influenced bile acid metabolism in mice. Environmental Pollution, 226, 268–276. doi:https://doi.org/10.1016/j.envpol.2017.03.068

Motta, E. V. S., Raymann, K., & Moran, N. A. (2018). Glyphosate perturbs the gut microbiota of honey bees. Proceedings of the National Academy of Sciences, 115(41), 10305–10310. doi:10.1073/pnas.1803880115

Rook, G. A. W., Lowry, C. A., & Raison, C. L. (2013). Microbial ‘Old Friends’, immunoregulation and stress resilience. Evolution, Medicine, and Public Health, 2013(1), 46–64. doi:10.1093/emph/eot004

Schnorr, S. L., Candela, M., Rampelli, S., Centanni, M., Consolandi, C., Basaglia, G., . . . Crittenden, A. N. (2014). Gut microbiome of the Hadza hunter-gatherers. Nature Communications, 5, 3654.

Yong, E. (2016). I Contain Multitudes: The Microbes Within Us and a Grander View of Life: HarperCollins.