Food for Thought?
by Guest Blogger,
Tyler Kokjohn, Ph.D.
Our gastrointestinal (GI) tracts are home to billions of microbes. Microbiologists have known for a long time our guts are well colonized, but the full complexity and importance of the GI microbiome was recognized only recently. Around 1,000 different bacterial species may reside in this part of our bodies during the course of our lives (1).
The microbial universe hidden within us exerts major impacts on our physiology, development and perhaps much more (1,2). Gut microbes produce neurotransmitters (1) which may influence diverse activities such as cognitive function, social interactions and adaptive responses to stress (1,3,4). However, communications flow in both directions. The brain is hardwired into the GI tract directly by the vagus nerve and may modulate microbial activities through several mechanisms (4,5,6). Animal studies have shown that the composition and metabolic activities of the gut microbiome are sensitive to stress (5) and disrupting it may produce serious consequences.
Aging and low fiber diets impoverish the gut microbiome (7,8). These observations invite speculation that modern day eating habits are promoting a broad range of pathologic conditions including age-related frailty (7). It literally gets worse – experiments with rodents suggest gut microbiome diversity may drop with each new generation (8). Perhaps our diets have accidentally driven the microbial symbionts essential for robust health to extinction and hastened the onset of maladies such as Alzheimer’s disease (AD) or worsened their impacts (9).
Although to this point most of the experiments manipulating GI microbiomes have been conducted in rodents, the implications for human health could clearly be staggering (10). We share our microbial passengers with others through casual contact, could some conditions regarded as purely mental (brain) diseases actually be contagious? Persons who maintain social interactions in old age seem more likely to avoid AD. Maybe the long noted cognitive benefits of social engagement are partially due to periodic re-inoculation with essential bacteria that would otherwise be lost with aging and physical isolation. The GI microbiome is dynamic and perhaps one day physicians will maintain and promote mental wellbeing by prescribing ‘psychobiotics’- probiotic microbe-containing supplements analogous to foods like yogurts (10, 11).
GI microbiome research is currently in the unbounded optimism phase. Fecal transplants are being used to help patients recover from severe Clostridium difficile infections of the GI tract (12). OpenBiome, a non-profit organization, now distributes healthy donor fecal samples in pill form to facilitate treatment and research. Undoubtedly amazing new insights and some novel approaches to improve human health are in the offing. Although companies are moving ahead quickly (11) scientists are attempting to manipulate still largely unexplored living ecosystems and not every good idea is sure to become a miracle cure. The efforts to eradicate C. difficile infections provide an instructive example. While fecal transplants have produced remarkable benefits, how they work is still unknown and recent clinical trials of similar strategies have produced disappointing outcomes (13). Medical issues like obesity and AD are equally or more complex and it seems likely that improved diets and probiotics will be only one facet of correspondingly complicated future management strategies.
Why we’re here. We founded OpenBiome, a nonprofit 501(c)(3) organization, after watching a friend and family member suffer through 18 months of C. difficile and 7 …
(1) T. G. Dinan et al. 2015. Collective Unconscious: How Gut Microbes Shape Human Behavior. Journal of Psychiatric Research 63:1-9. http://www.sciencedirect.com/science/article/pii/S0022395615000655
(2) E. P. J. G. Neis et al. 2015. The Role of Microbial Amino Acid Metabolism in Host Metabolism. Nutrients 7:2930-2946. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4425181/
(3) P. A. Smith. 2015. The Tantalizing Links Between Gut Microbes and the Brain. Nature 14 October 2015, (526:312-314). http://www.nature.com/news/the-tantalizing-links-between-gut-microbes-and-the-brain-1.18557
(4) S. Reardon. 2014. Gut-brain Link Grabs Neuroscientists. Nature, 12 November 2014, (515:175-177). http://www.nature.com/news/gut-brain-link-grabs-neuroscientists-1.16316
(5) E. A. Mayer et al. 2014. Gut Microbes and the Brain: Paradigm Shift in Neuroscience. The Journal of Neuroscience 34(46):15490-15496. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4228144/
(6) C. Schmidt. 2015. Thinking From the Gut. Nature, 25 February 2015, (518:S12-S15). http://www.nature.com/nature/journal/v518/n7540_supp/full/518S13a.html
(7) P. W. O’Toole and I. B. Jeffery. 2015. Gut Microbiota and Aging. Science 350:1214-1215. http://science.sciencemag.org/content/350/6265/1214
(8) K. H. Courage. 2016. Your Poor Diet Might Hurt Your Grandchildren’s Guts. Science 13 January 2016. http://www.sciencemag.org/news/2016/01/your-poor-diet-might-hurt-your-grandchildren-s-guts
(9) S. Bhattacharjee and W. J. Lukiw. 2013. Alzheimer’s Disease and the Microbiome. Frontiers in Cellular Neuroscience 7:153. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3775450/
(10) L. Sanders. 2016. Microbes Can Play Games with the Mind. Science News, 23 March 2016. https://www.sciencenews.org/article/microbes-can-play-games-mind
(11) S. Reardon. Microbiome Therapy Gains Market Traction. Nature, 13 May 2014, (509:269-270). http://www.nature.com/news/microbiome-therapy-gains-market-traction-1.15210
(12) P. A. Smith. 2015. Fecal Transplants Made (Somewhat) More Palatable. The New York Times, 9 November 2015. http://www.nytimes.com/2015/11/10/health/fecal-transplants-made-somewhat-more-palatable.html?_r=0
(13) R. Cross. 2016. Poop Pill’s Surprising Failure Shows that the Microbiome is Still a Mystery. MIT Technology Review, 29 July 2016. https://www.technologyreview.com/s/602044/poop-pills-surprise-failure-shows-that-the-microbiome-is-still-a-mystery/