The World within Us May Control Us

iStock_000011861815LargeBy Kevin McPherson, Emory University

Remember that old saying, “You are what you eat?” I don’t really remember where I heard it first, but I think it was somewhere in elementary school. As a six year-old, the saying immediately brought images of me as a giant peanut butter and jelly sandwich. It sounded pretty cool to me at the time. However, I think this saying has caught up to me, and the saying itself may be gaining more validity as research surrounding the human microbiome is growing. Recent research points to the eerie idea that the microbiome in our bodies could be affecting our behavior, and maybe even our mood.

It all sounds much like a science fiction novel when you think about it. How might our microbiome do such things? First, we should look at the rest of the natural world to get an idea of this type of relationship. There appears to be other parasite-host relationships that work in more insidious ways. For instance, take the fungus Ophiocordyceps unilateralis and its interaction with the ant Camponotus leonardi. Researchers have shown that the fungus can infect ants and essentially control their bodies. The ants clamp onto the underside of leaves and die in this precarious position, allowing the fungus to grow out of the dead ant’s body and shower uninfected ant populations with new spores. Pretty morbid, huh?

Luckily, we don’t have to worry (just yet) about these types of interactions with our microbiome, but I do think that the fungus-ant relationship calls our attention to a myriad of concerns that have yet to be addressed: how might we be able to appease our microbiome? Does our microbiome change over time based on our eating habits? Are our eating habits being affected by our microbiome? The research is all preliminary, according to leading microbiologists, but these questions take a different perspective on how we might view our microbiome. Rather than seeing the microbiome as something that protects us and helps us, we need to be cognizant that it may also be controlling us for its own benefit.

This perspective has a valid stance: studies in mice in which the so-called “gut-brain axis” (or the biological telephone line between the gut and the brain) was examined show that when researchers replace the microbiome of a fairly “bold” mouse with that of an “anxious” mouse, their behavior seems to mirror each other. That is, the microbiome replacement seems to make the “bold” mouse more anxious. Other curious discoveries have shown that certain bacteria in humans can actually thrive on the digestion of chocolate, thus explaining your insatiable chocolate cravings. Your body does not need chocolate, but bacteria inside you might, thus causing changes in your dietary behaviors that benefit bacteria and not you.

Our microbiomes cannot be reduced to a simple host-parasite relationship. Many studies have shown that mice that grow up in germ-free environments actually tend to avoid other mice and have a harder time establishing social ties. The social bonding is good for the mice, but it is also beneficial to the microbiome as they search for different host organisms (i.e., other mice). Obviously, there seems to be both a practical and a beneficial side to our relationships with our microbiome.

There are still a lot of unanswered questions about the microbiome, and research is just beginning to explore the symbiotic relationship between humans and the microbes found in our guts. Maybe one day, deeper understanding of microbiome will help us treat specific metabolic diseases. For instance, a pre-diabetic could have their microbiome replaced so that they crave healthier foods. A lot of research remains to be done on which strain of bacterium elicits what behavior. And deciphering that could be the difference between life and death for both humans and the bacteria.



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