Having just completed my microbiology final, I thought it would be appropriate to write a little bit about the microbes that live in and on us, and how they affect our health. The widely quoted statistic is that there are 10 bacterial cells for every human cell in your body, which I find an overwhelming notion when I really think about it. That’s literally hundreds of trillions of independent organisms colonizing your body that you cannot even observe. Scientists are just beginning to have a smidgen of an understanding of the complexities and the implications of the human microbiome, but there is no question that these bacteria have a huge role in both keeping us healthy and making us sick.
The first thing that’s important to point out is that most of these bacteria with whom we are living in concert are beneficial to us. We tend to think of microbes as inherently germ-y and unsanitary, but that mindset leads us to be inclined to keep our world sterile, which the medical community is beginning to understand is actually dangerous. We should not try to rid ourselves of all microbes, because they actually help us do some pretty important things. Two big ones are digestion and immunity.
The stomach is a pretty hostile environment and its acidity helps to kill any pathogenic organisms that find their way in there, but your intestines, small and especially large, are full of more bacteria than you can imagine that help you digest the food you eat. For instance, we cannot absorb certain types of fiber or short chain fatty acids, but there are bacteria in the colon that ferment it to compounds we can absorb (and occasionally gas). Since different bacteria thrive on different nutrient sources, you can imagine that people on different diets would have different types of bacteria in their GI tract. Conversely, many scientists are finding some evidence showing that the bacteria in our guts influence what food we crave. So it might just be a vicious cycle where if you eat junk your gut bacteria will make you continue to crave junk or you eat lots of wonderful fibrous plant foods and your gut bacteria make you crave those instead. There’s no firm evidence about what’s causing what yet, but a person’s microbiome is often associated with whether or not they are obese, have addictive tendencies, have a given chronic illness, or particularly if they have digestive issues. That’s why many people take probiotics, to try to shift the microbial population of their gut in a positive direction. That’s also why doctors are experimenting with fecal transplants (yes, you read that right, look it up).
With regard to immunity, there are two important concepts I want to put out there. One is that, according to my understanding, there are actually bacteria in your body that help fight infection by competing with pathogenic bacteria and viruses, so you wanna keep those guys around. The other is that the way your immune system actually develops is to be exposed to germs and pathogens and learn how to fight them. That’s why you can never get the same virus twice. The idea that I’m being more and more convinced of is that if we try to stay too clean, so to speak, our immune systems never learn to tell friend from foe, so not only can truly toxic pathogens hurt us more, but we can have inflammatory responses when there is no real danger at all, as in most allergies and auto-immune diseases.
Of course, there’s a fine line here. We need a very delicate balance of how many anti-bacterial substances we use, especially routinely. Chlorinating our water supply prevents cholera epidemics but evidence has shown that it actually may have made us more vulnerable to polio. There are times you really need antibiotics to cure an acute infection, and there are times when they cause more harm than good (eh-hemm, routine non-therapeutic use in livestock production).
This post was kind of all over the place, but that’s how I feel about this topic — it’s so unbelievably complex and nearly impossible to pin down using the conventional paradigm of reductionism in the scientific world. Reductionism has its place, for sure, but I don’t know if we’ll ever be able to piece together the microbiome one cause-and-effect at a time.
Some areas of research involving the microbiome are more developed, while others are just in their infancy. I’m very excited to keep learning; there have already been some major health innovations in this field and I suspect there will be more.