Evolutionary Mismatch, the Human Biome…and a Bit More on Obesity

Recently there was a lot of discussion on the Biome Buzz’ Facebook page in regards to a post on obesity, wherein some people expressed their opinions that our current epidemic of obesity is due to nothing more than people eating too much junk food.  While there is zero doubt that diet is a (probably THE) major factor, I pointed out that it is not that simple.

Dr. William Parker, et.al., of Duke University Medical School, wrote a paper back in 2013 which described the concept of “evolutionary mismatch.”[i]  This encompasses the idea that through evolutionary pressures (survival of the fittest), our bodies have developed in such a way as to account for the presence of our “old friends” (the trillions of organisms that co-exist in us) and modern living has deprived us of that which is now necessary for our bodies to function properly:  “Species depleted or even eliminated from the human biome include a wide range of pathogens, commensals and mutualists whose reproductive cycle is greatly diminished or even eliminated by modern sanitation, water treatment and medical practices…The absence of species from the human biome leaves the immune system in a hypersensitive state that, when combined with environmental triggers and genetic predisposition, leads to allergic and autoimmune disease. The wide range of evidence pointing incontrovertibly at this conclusion…”

My regular readers are very familiar with this idea as nearly every post I have written over the years describes the emerging science that connects biome depletion to our current epidemic (in the industrialized world) of chronic, immune-related illness.

I read a really interesting article yesterday that further explores this idea.[ii]  These authors, from the University of Louisville, examine the idea of evolutionary mismatch and natural selection, in light of biome depletion and the effect upon public health – and forward some ideas of how our society can (and must) deal with this threat.

So a few really interesting bits from the paper:

1. Many (if not most) microorganisms’ effects on human health are unknown.  They refer to these organisms as “indeterminate symbionts,” defining a symbiont as an organism that lives “intimately with other organisms.”  Commensal organisms are symbionts that have “neither a harmful nor beneficial overall effect.”  If you imagine a spectrum then, commensal is the dividing line between parasites and mutualists (those organisms that benefit the host while themselves, benefiting from the host).

2. Some organisms are “strong mutualists,” and are at the far end then of this spectrum on the beneficial side. They provide an example in the Bifido strain, infantis. In infants, “It releases antibacterial compounds that inhibit pathogenic bacteria, synthesizes vitamins, improves immunological responses, and protects premature infants against ulcerative colitis.” And guess what?  Human breast milk is uniquely suited to helping B. infantis grow, with its rich supply of human milk oligosaccharides (prebiotics), which are particularly suited for this organism.  “The diversity of HMOs produced in milk appears to have coevolved for B. infantis more than for any other bacterium.”  Thus, the increased use of formula – which contains neither the probiotic, B.infantis, nor the prebiotic, sets babies up for a myriad of health issues.

A paper appeared in 2018 from the American Academy of Pediatrics, that states “…breastfeeding has many established benefits for child health; in fact, previous meta-analysis of research found that breastfed infants have a 26 percent reduced risk of obesity later in life. In a study in the October 2018 Pediatrics (published online Sept. 24)… researchers found that breastfeeding was associated with lower body mass index (BMI) and a reduced risk of excessive weight gain in the first year of life.”

From an evolutionary standpoint, “The mismatch between formula feeding and breast feeding is a particular example pertaining to a dietary change because infant formula differs from breast milk.”[ii]  Thus, by not feeding the infant’s developing microbiome as nature intended, we have created an evolutionary mismatch that is associated with obesity (and other chronic diseases) later in life.  Another recent paper looked at the gut bacteria in 2 year old children (who had no weight issues), and correlated this to obesity by the age of 12: “One recent study in this regard showed infant gut microbiota could be used as a biomarker to identify the children who are at risk of becoming overweight and obese later in childhood. That study…concludes that gut microbiota composition at 2 years of age can be used as a predictor for obesity at age 12. Although the toddlers may not be overweight or obese at 2, the research identified a correlation between their gut microbiota composition at early stages and their body mass index (BMI) at 12.”

3. On this same subject (i.e. obesity): there have been many papers lately pointing out that gastric bypass surgery improves insulin sensitivity even before weight loss has occurred.  “The rapidly ameliorating effects of gastric bypass surgery are consistent with microbiome influences on diabetes, which could occur quickly as a result of the short generation times of bacteria.  Gut microbiota are strongly affected by gastric bypass surgery.”[ii]  Another coincidence (that you all know I love):  an article on this appeared this morning on Gut Microbiome for Health which states,   “…interactions between the gut microbiota and bile acids metabolism may partially mediate the success of bariatric surgery in the medium term…the authors showed specific core gut microbiome profiles, with patients from the success group showing the most diverse gut microbiome”  In fact, success of the surgery appears to be reliant upon the composition of the gut bacteria.

4.  The authors point out that different microbes have a greater and lesser affinity for glucose. Those that thrive on it are essentially competing with their host human for the molecule. For example, Staphylococcus aureus loves glucose.  Therefore, it releases a peptide (short string of amino acids) that binds to insulin and blocks it from uptake by human cells, thereby increasing the amount of available glucose to the microbe, and “favoring insulin resistance” in the human:  “In a study assessing the relationship between neonatal microbiota and obesity seven years later, S. aureus was found in the fecal samples that had been taken from obese 7-year olds when they were neonates, whereas bifidobacteria dominated the neonatal feces of children who did not become obese.  Accordingly, breast feeding is associated with a substantially reduced probability of being overweight or obese during childhood.”

5. And of course, our modern “western” diets are a complete evolutionary mismatch: “The evolutionary mismatch of a diet low in fiber and high in sugar and fat and the radical increase in formula feeding have led to near global disturbance of the human gut microbiome with shifts in species diversity and proportions.”

6. Other illnesses that are clearly associated with evolutionary mismatch, according to this article, include celiac disease, diabetes, obesity, as I just mentioned, autism and allergies.  (Dr. Parer’s paper has a far more extensive list.) A quick example:  in a mouse model, infantis ameliorates allergy:  “Has the nearly worldwide shift to vast numbers of children being formula fed…led to a reduction in the population level prevalence of important gut bacteria for the newborn?”

7. One new vocabulary word for all of us:   There are organisms, which I have actually written about several times before, that, depending on environmental circumstances, are either parasitic or mutualistic.  The paper provides an example:  the bacterium, Bacteroides thetaiotaomicron, which is a commensal organism that is ordinarily mutualistic (in that it breaks down non-digestible carbohydrates into sugars usable by us)…unless it is in the presence of E.coli, in which case, it exacerbates the damage caused by this parasitic bacteria.  From now on, I’ll be using that term – ambisymbiont – when talking about such organisms.  I like it!   It has a ring to it…

8. Back to my the paper I mentioned in the opening paragraph: Parker et. al. point out that our modern diet and the decrease in breast feeding are just two of the current evolutionary mismatches to which we humans (and our domesticated pets, by the way) are subjected.  Others include our general lack of exposure to sunlight, in regards to vitamin D production, potentially “unrequited psychological stress,” and the eradication of our native macrobiomes.  “The identification of biome depletion as the cause for pandemics of immune disease carries with it a solution:  biome reconstitution.  Although the extent to which biome reconstitution can reverse disease remains unknown at present, biome reconstitution is hypothetically a readily available means of preventing disease associated with biome depletion.”

Or…as today’s paper concludes:  “Public health efforts to counter negative effects of the Western diet, support breastfeeding, and assure access to high-fiber, low-sugar, and low-fat foods may have an outsized effect on seemingly unrelated widespread diseases such as diabetes, autism, and childhood obesity.”


[i] Parker, W and Ollerton, J.  Evolutionary biology and anthropology suggest biome reconstitution as a necessary approach toward dealing with immune disorders. Evolution, Medicine, and Public Health. 2013;89-103.  doi:10.1093/emph/eot008

[ii] Ewald, HAS, Ewald, PW. Natural selection, the microbiome, and public health.  Yale Journal of Biology and Medicine. 2018;91:445-455.

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