Human Microbiome

October 1, 2020

Important Points:

  • Microbiome
  • Bacteria
  • Storage
  • Human Microbiome

We traditionally think of bacteria as dirty, something we want to keep outside of our bodies.  Intestinal bacteria are very important for digestion; they break complex fiber polysaccharides (sugar molecules connected to each other) into simple absorbable sugars by a process called fermentation, converting nutrients into calories.  The large intestine alone houses over 1400 species of bacteria numbering over 100 trillion.  In reality, the human body contains ten times more microbial cells than human cells, and the human body is dependent upon the genetic information encoded in these bacterial cells for specific metabolic pathways.

Our microbial partners have co-evolved with us, in a beneficial (symbiotic) relationship involving nutrient sharing.   The ability to store energy would be a beneficial attribute for ancient humans as they had variable access to food.  When nutrient dense food supply was available, their consumption and storage would benefit both them and their bacterial symbiotes later when food supplies were diminished. However, in modern, developed societies where there is ready access to large-portion, high-calorie diets, this “benefit” becomes a detriment, and we develop a previously rare condition called over-nutrition, over-storage, or obesity.

Obese individuals have a different mix of bacteria in their guts than thin people. The ratio of Firmicutes to Bacteroidetes (called the F/B ratio) is higher in obese people than in lean people, and it drops as those people lose weight. Both Firmicutes and Bacteroidetes bacteria are involved in complex polysaccharide breakdown, but Firmicutes are much more efficient than Bacteroidetes bacteria; therefore, having more Firmicutes bacteria in our gut makes more energy available leading to increased caloric intake and eventually obesity.  Firmicutes overload is also associated with slowed intestinal motility, commonly known as chronic constipation.

In studies of genetically identical twins, bacterial populations have been found to differ, depending on whether the twin is lean or obese, with much higher level of Firmicutes in the obese twins.  In obese patients undergoing gastric bypass surgery, colonic bacteria change to become more like those of normal-weight individuals after the operation, reducing their Firmicutes levels.

Antibiotic over utilization may also indiscriminately eradicate the beneficial bacteria in your gut along with the bad ones.  Conventional farmed meats are doped with antibiotics, with nearly 50-70% of all antibiotics produced in the United States used on healthy livestock to promote growth and weight gain in the animal feed.  Consuming these antibiotic-laden meats may be a significant factor enhancing growth and weight in the human population [obesity] as well.  Eating grass-fed and organically raised meats of all kinds can reduce this antibiotic intake.

The amazing thing to keep in mind is that you can rapidly – within 72 hours – change your gut bacteria to a healthy ratio simply by immediately eliminating refined carbohydrates and increasing your fiber intake.  Supplements of “get thin bacteria” will soon be available as well.

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