It is generally well known that the reason ruminants are able to digest grass, while we can’t, is that they have special bacteria living in their stomachs which can break down the indigestible plant matter into a form that can be absorbed by the cow.
What is perhaps not so well known, is that although we may not have the kinds of bacteria that can break down grass, we do in fact rely on other types of bacteria for the breakdown of much of our food, and that without our invisible internal allies we would literally waste away!
Studies of germ-free mice – That is mice which have no gut flora – Have shown that they need to eat 30% more calories that normal mice in order to maintain the same bodyweight. (Sears, C. L. 2005)
Sequencing of the genomes of human gut flora has shown that our microbiome is capable of producing enzymes for the breakdown of carbohydrates and lipids which we ourselves are otherwise unable to digest and absorb. (Sears, C. L. 2005)
In addition to increasing the amount of energy we are able to absorb from our food, our gut flora is also essential for the extraction and absorption of the micro-nutrients in our diet. It is the good bacteria in our intestines that synthesise Vitamin K, Biotin and Folate from our foods, and also facilitate the absorption of minerals such as Magnesium, Calcium and Iron. (O’Hara and Shanahan, 2006)
Without the necessary strains of bacteria present in your gut, it wouldn’t matter how much nutrient dense food you consumed, as the vitamins and minerals within would remain inaccessible to you.
Your microbiome also aids digestion in a third way – Rather than simply floating around in your intestines breaking down indigestible foods into easily absorbed particles, the gut flora actually interact and communicate with the intestinal lining. The presence of beneficial bacteria has been shown to lead to the expression of more nutrient transporters in the epithelium, and an increased proliferation of capillaries within the intestines, thus further increasing the uptake of energy and nutrients from the diet.(Sears, C. L. 2005)
Aiding digestion is just one role of the microbiome however, in part III we shall be looking at the role of gut flora in immunity, and why taking anti-biotics can be disastrous to your health.