A universe of organisms living inside you may affect every part of your body, from your brain to your bones, and even your thoughts, feelings and your attempts to lose weight.
This is a universe of trillions of microorganisms – or what we biologists call microbiota – that live in your gut, the part of your body responsible for digestion of the food you eat and the liquids you drink.
As researchers, we have been looking increasingly into the effect these bacteria have on their host’s body, from obesity to mental illness and heart disease. With obesity, for example, these tiny organisms may play a big role by influencing what foods we crave and how our bodies hold onto fat.
In a recent study of the gut microbiome, we set out to determine whether the microbiota in the gut can be affected not only by our nervous system but also by an unsuspected source – our bone marrow.
Our hope is that, by understanding the interactions of the microbiome with other parts of the body, one day treatments could be developed for a range of illnesses.
The gut-brain-bone marrow connection
The gut, which includes your esophagus, stomach, small and large intestines, colon and other parts of your digestive system, is the first line of defense and the largest interface between the host – in this case, a person – and the outside world.
After birth, the gut is the first point of entry for environmental and dietary influences on human life. Thus, the microbiota in the gut play a crucial role during human growth, as they contribute to development and maintenance of our immune system throughout our lifetime.
While we initially thought of the microbiota as relatively simple organisms, the fact is that they may not be so simple after all. Gut microbiota can be as personal and complex as a fingerprint.
There are more bacteria in your gut alone than cells in your entire body. This vast bacterial universe contains species that combined can have up to 150 times more genes than exist in humans. Research suggests that the bacteria in our gut predates the appearance of humans and that they may have played an important role in evolutionary separation between our ape ancestors and us.
Healthy bacteria actively interact with the host immune system in the gut. They contribute to the barrier between disease-causing microorganisms or infections introduced via ingestion. They also help prepare the host immune system to defend the body. The wrong mix of microbes, on the other hand, can contribute to many digestive, immune and mental health disorders and even obesity.
These tiny organisms work very hard in digestion. They help digest our food and can release nutrients and vitamins essential for our well being, all in exchange for the privilege of existing in a nutritious environment.
Researchers are actively exploring the many facets of this symbiotic relationship. Recent data show a link between gut microbiota diversity and richness and the way we store fat, how we regulate digestion hormones and blood glucose levels, and even what types of food we prefer.