The human body carries trillions of bacteria, viruses, and other tiny microbes. Think of your body as a living/breathing rain forest. Scientists call these resident bugs and all of their genes the “human microbiome.”
Some of these microbes can be harmful, but most have lived and evolved with humans for thousands of years. They help train our immune systems to attack only foreign invaders, not our own joints and organs, and they pull essential nutrients out of the food we eat.
Today, people in the Western world have far fewer kinds of these helpful bacteria than their cousins in developing countries and that might be connected to rising rates of autoimmune diseases, such as asthma, and metabolic ones, such as obesity and type 2 diabetes.
Throughout our lives, we help shape our own microbiomes — plus they adapt to changes in our environment. For example, the foods you eat, how you sleep, the amount of bacteria you’re exposed to on a daily basis and the level of stress you live with all help establish the state of your microbiota.