You Are What You Eat

The common saying goes, “You are what you eat.” However, there may be more to that saying than you think. Other than the food that we digest, there are also at least 1000 different species of bacteria living in our gut. On top of that, there’s a growing group of evidence that suggests that there is an intricate connection between the bacteria in our gut and our brain activity.

The gut microbiome is used to describe the diverse population of microorganisms living inside our gastrointestinal (GI) tract. These microorganisms include bacteria, fungi, viruses, and many other tiny creatures, if you could call them that. We commonly have the conception that such microorganisms are detrimental to our health, but quite to the contrary, having a diverse community of these gut microorganisms is essential for a person’s wellbeing. In a healthy person’s GI tract, it is estimated that there are 50 different phyla of bacteria, 1000 different bacterial species, and 10^14 viable bacteria per gram of lamina, which is the tissue that lines our GI tract. These numbers don’t include all the other microorganisms, like fungi and bacteriophages, living in our gut! Looking at these numbers, it’s easy to see that we have a diverse community of microorganisms living inside our bodies. We call the diversity of the microbiome in our bodies the microbial fingerprint.

Diet plays a large factor in the diversity of the gut microbiome. For example, changing your diet for a short term period into one of entirely animal or plant products can drastically and quickly change the kinds of microorganisms living in your GI tract. On the other hand, having a diverse diet is associated with a diverse gut microbiome, which in turn leads to better health for an individual.

The importance of the gut microbiome even extends to mental health. Over the years, research has continued to indicate that the gut microbiome affects many aspects of brain activity, such as emotional behavior. It may even affect the pathophysiology of mental illness. The communication between the microbes in the GI tract and the brain is called the gut-brain axis. The gut microbiome affects the nervous system by secreting vitamins, neurotransmitters, and metabolites. It is thought that gut microorganisms can also send signals up to the brain through neuroimmune and neuroendocrine pathways. In turn, the central nervous system affects the GI microbiome through the nerves by regulating secretory functions and the mobility of the GI tract.

Several health conditions are associated with faulty gut-brain communication, such as Irritable Bowel Syndrome (IBS) and inflammatory bowel disease. Many studies concerning the gut microbiome have been conducted on germ-free animals, which don’t have a gut microbiome. Germ-free mice mimic health problems associated with altered gut-brain axis, not only gut problems but also mental problems, showing abnormal development. One way that the gut microbiome affects the brain is by influencing neuroinflammation in the brain by modulating microglial activity, the brain’s defense mechanism. This in turn affects myelination of axons and neurogenesis, which mean, respectively, the speed of neural activity and the formation of new neurons. Many recent studies show how germ-free mice have learning deficits, anxiety-like behavior, and reduced sociability.

However, these mice can be somewhat rescued, through a process called a fecal transplant. Fecal matter of non-germ-free mice, which contain healthy gut microorganisms, are transplanted into germ-free mice. These mice then have less severe health problems, both physical and mental, due to the introduction of a healthy gut microbiome. These studies reinforce the idea that the gut microbiome is essential in physical and mental health.

So what can we do with this information? We know that what we eat affects our gut microbiome, and our gut microbiome can affect both our physical and mental health. These findings emphasize the importance of a diet diverse in many vitamins, proteins, and nutrients, so that we can have a healthy gut microbiome and a healthy life. So, be mindful of what you eat!


Mary Yoshikawa