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Are we really human?

microbiome art II

We are only 10% human. When put like that, I get a new perspective on the meaning of life.  The genetic material defining who we are is made up from microbial and human genes.  Our bodies are made up of 150 fold greater number of genes from microbial DNA than human DNA.  Microbial cells outnumber human cells ten to one. Microbial includes bacteria, fungi, archae, and viruses.  This microbe pool, otherwise known as our flora or microbiome, exists in niches on our skin, mouth, GI tract, and genitals. While I always knew of the flora balance, I never really thought about the cellular metabolism and the resulting metabolites from our microbes as a powerhouse in sheer numbers compared to our human cells. I have a new respect for microbial metabolism as I think about what is necessary to keep this critical symbiotic relationship in balance.  Microbes are adaptable to the environment, thereby enabling us to adapt to the environment. The balance of our microbiome is therefore a critical part of our health. Genetic sequencing of our microbiome is a fairly recent undertaking and there is a whole new story emerging.

I always knew variety was the spice of life.  Different species of microbes have different metabolisms and release a variety of metabolites including neurotransmitters (such as serotonin); enzymes, vitamins (notably Bs and K), other essential nutrients (such as important amino acid and short-chain fatty acids), cytokines, and other signaling molecules that influence the immune and the metabolic systems. These metabolites provide us our nutrients and cofactors that aid in digestion, protect us from pathogens, train the immune system, participate in neural signaling, and strengthen the intestinal barrier.  We can almost think of ourselves as a skeletal, muscle support for our microbe’s ecosystem.  Almost.

Patterns are emerging in the composition of species that make up our microbiome.  Specie microbe patterns across regions, time, age, and health will inform us of microbiome balance for optimal health. One pattern is already emerging in the infancy of the data mining project.  More diversity is better than less. A diverse ecosystem is more resilient. Diversity in the Western gut is significantly lower than in other, less-industrialized populations and diet and antibiotic uses are right up there as large culprits for reducing our microbiome diversity.

Another pattern observed is the effect of diet on the microbiome. The food you eat is the largest determinant of your microbiome diversity and abundance.  Through the analysis of gut microbiomes across different regions of the world, a pattern of our species composition is emerging.  Regions that have the longest life expectancy across the world, referred to as longevity hot spots, have a distinctly different microbiome than many industrialized nations.  One common element that these longevity hot spots share are large amounts of plants in their diets. Their microbiome is more diverse and contain more of the phyla (Bacteriodetes) than subjects on a Western diet.  The food you eat determines your metabolism, immune activation, nutrient absorption capacity, digestive ability that is all driven by the microbes in your gut.

Because microbes are so adaptable, significant changes to your diet can change your genetic make-up, at least the large percentage of your genes coming from your microbial colonies.  The genetic makeup of your microbes is a large determinant in health.  I don’t know about you, but I feel so empowered when I think that I have quite a bit of control over my genetic make up.

The large increase in inflammation observed in people is believed to be the basis for a number of chronic illnesses.  We will consume over 50 tons of food in our lifetime that our microbiome will metabolize to provide the rest of our body with essential nutrients.  The epithelial cells making up our intestinal wall require short chain fatty acids that nourish and strengthen this barrier.  The short chain fatty acids are bacteria byproducts or metabolites from their fermentation of plant fiber.  Reduced numbers of the Bacteriodetes phyla of bacteria, which metabolize plant fibers and provide short chain fatty acids, results in increased permeability of the intestinal barrier and thought to play a large role in inflammation.  If inflammation is chronic, the permeability of the barrier increases. This increased permeability hyper activates our immune systems as the contents from of our GI tract leak into the blood stream.  A diet high in processed foods is likely starving this phyla of bacteria known to occupy the large intestine and play an integral part of nourishing this section of the intestinal wall.

I look forward to the results from the Human Microbiome Project revealing more on the mutualism between human and microbe. In the mean time, I’ll keep eating kale salads to feed the microbes that are responsible for nourishing the intestinal barrier.  This is sure to bring happiness to all of me.

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