Gut Reactions

The microbiome is everywhere these days. You can’t walk down a magazine aisle or scroll a news site without seeing something about gut health. And that’s for good reason – research on gut health is one of the fastest growing areas of research in science. There’s string theory and there’s gut health. And the vastness of those two concepts is not that different.

What we know about gut health, which involves a balanced and diverse community of microbes (microbiota) that live in the human digestive track, is that gut health impacts everything from digestion to immune function to mood and mental health. The impacts on mental health are fascinating and have led researchers to coin the term “gut-brain axis” which is defined as a bidirectional communication network where microbiota produce neurotransmitters (like serotonin and dopamine) that regulate mood, happiness, and emotions. Good gut health is associated with positive mood and emotional regulation while poor gut health is associated with negative mood and emotional regulation. 

While this particular correlation has been known for some time, the mechanism has been more difficult to uncover. But new research has not only identified how different species of microbes impact mood and behaviour, with some species even correlating to more social behaviour in the host, it has also identified how these microbes might communicate – with us.

When we think about our senses, we think about the obvious ones. Sight, smell, touch, taste, sound… each of these senses transforms the physical world around us into something our brains can make sense of. And this transformation occurs at a cellular level in sensory cells like photoreceptors, mechanoreceptors, and olfactory neurons. Dr. Maya Kaelberer, a researcher and professor at the University of Arizona College of Medicine discovered another type of sensory cell in the gut, called a neuropod, that rapidly communicates to the brain. These cells detect what we eat, how much, but also potentially a felt sense of the value of the food we’ve eaten.

These transmissions occur when the bacteria that live in the digestive track shed small proteins when there is food around. When there is not food around, they stop shedding. When the neuropods sense these proteins, they send signals to the brain. Dr. Kaelberer hypothesizes that the signals are what contribute to feelings like “yes, that was a good food decision” or “I really want some sugar” or even specific cravings for foods that are high in certain micronutrients. And if these signals contribute to those feelings and those feelings contribute to behaviours, then it is not a stretch to suggest that our gut health and microbiome influence our behaviour in a direct way.

An example is geophagia. A form of pica common in children that involves eating soil. It often signals an iron or zinc deficiency. Minerals like iron and zinc can be measured in the blood and that’s how doctors know this about this correlation. What exactly sends the signal to the brain to consume dirt has not been identified but it’s highly likely that it is related to these neuropods. This is a very specific example; there are others that are less extreme.

And maybe we’ve always known this. Even if we haven’t known why or how, we’ve felt it. Because our gut sense is one of our oldest senses. The field of research that is investigating the gut-brain connection is young. Too young to draw conclusions but that doesn’t stop gut-health related products from lining the shelves of stores. Do these products help? Maybe, maybe not. So far, all the data surrounding gut health and microbiome diversity supports a balanced diet. So, while we wait on science to uncover more about this unique mechanism that has the potential to positively impact almost every area of human health, we can focus on eating fibre, leafy greens, and lean protein and assume that the positive gut health associations that we already know about are just the tip of the iceberg lettuce.