by Emily Green
What does it mean to be an individual? Perhaps you enjoy spending your time doing a particular hobby or playing your favorite sport. Maybe you like to express your interests through the clothes you wear or the music you listen to. Whatever your passions may be, each and every one of us are unique—different from one another. And while we may all be unique, what if I told you we are never truly individual organisms? We actually have trillions of microscopic organisms living on and inside our bodies, distinctly different from ourselves. In fact, only 50% of the cells in our bodies are human cells. The other 50% are made up of bacteria, fungi, and viruses, collectively known as the microbiome.
These microorganisms exist all over our bodies: in our gut, on our skin, in our mouth. Each region houses microbes that thrive in different ecological niches formed from the specific conditions of that body part. For example, microbes present in the stomach tolerate a very acidic environment, while microbes present on the skin tolerate a wide range of temperatures. These microbes have evolved to live in symbiosis with each other and ourselves. In a healthy individual, good and bad bacteria coexist to promote positive health, physiology, and development. They help us to metabolize, or break down food, and absorb nutrients in our intestines. They contribute to a strong immune system by colonizing, or living, on our skin and in our gut. They use up space and resources so bad, or pathogenic, bacteria cannot invade and cause infection (Figure 1). Microbes can even influence our behavior and development by directly communicating with our brain. Moreover, microbes can protect us from harmful toxins in our environment by facilitating xenobiotic metabolism, or the break-down of harmful chemicals into non-toxic byproducts that our bodies can metabolize and excrete.
However, if the balance between good and bad bacteria is disrupted, diseases may arise. The composition of our microbiome begins to form in utero, or before birth. Things such as the maternal diet, birthing method, infant feeding method, heritable genetics, and early life exposures play a role in forming our microbiome during early development. However, that is not to say the composition of your microbiome is set in stone from the first few years of life. Many lifestyle factors such as diet, exercise, aging, stress, antibiotic use, and exposure to environmental toxins can alter microbial diversity throughout life (Figure 2). If any of these factors cause a negative shift in microbial diversity, or dysbiosis, risk for obesity, diabetes, mental health disorders, gastrointestinal diseases, cardiovascular diseases, kidney diseases, and even cancer may increase (Figure 1).
This microbial ecosystem is highly dynamic, quickly responding to changes in our bodies and our environment to provide the energy we need to function and protect us from negative stressors we encounter. It has been shown that something as simple as changing your diet can alter the microbiome in as little as 24 hours! It is therefore important to practice a healthy lifestyle – eating a well-balanced diet and exercising – not only for ourselves, but for our microbiome too! Even though we cannot see these microscopic organisms living on and inside us, we know that we are not alone. These microorganisms are distinctly different organisms and yet have evolved to be a necessary part of our lives. We depend on our microbiome so greatly that we literally could not live without it!
