Have you ever wondered why we use sayings like “gut feelings” and “butterflies in our stomach”? When we’re nervous, we have a weird feeling in our gut. When we’re stressed, we may have a hard time using the bathroom. When we fall in love, we feel flutters in our gut. Our gut is an organ that interacts with so many systems in our body that it’s called the second brain [R].
It’s impossible to neglect the critical role of the gut on health. Many diseases are associated with gut imbalance and that’s because of the impact it has on the immune system, the body’s line of defense against infection and disease.
What’s in the Gut?
Our gut is not purely a digestive tract. It’s flooded with trillions of microbes, collectively known as the gut microbiome. The gut microbiome composition is unique for each and every individual; some have more bad bacteria (disease-causing) and others more good bacteria. These bacteria interact with our cells and affect health, in particular, immune cells.
The Gut Educates the Immune System
The immune system is a group of specialized cells and molecules that aim to patrol the body. Not only do they help with recognizing harmful, foreign substances, they also function to protect the body from malfunctioning (cancer) or from self-harm (autoimmunity). How do they recognize harm? Some immune cells are marked with a certain receptor on their surface- a receptor that has the ability to recognize a specific foreigner, attack it, and get rid of it.
How do these immune cells learn what receptor to express on their surface? Through the microbes in the gut- they act as the teachers [R]. So, a diverse microbiome, full of a wide range of different types of germs leads to a balanced, well-educated immune system, fully developed and prepared to tackle threats.
Experiments on germ-free mice (mice born without any microbes) show how crucial the gut is for maintaining a healthy immune system. Germ-free mice have an immature immune system that lacks the ability to ward off disease. But as soon as they are provided with some microbes, their immune system quickly matures and develops a more diverse profile of immune cells, making them capable of proper immunity.
Similarly, children born from a cesarean section have a higher risk of developing certain conditions like asthma, allergies, obesity, and type 1 diabetes because they are not exposed to the same microbes present in the delivery canal that offer more protection against these immune-related conditions [R].
These are just some examples of how we have come to understand the impact of germs living in our gut on our immunity. Immune cells are primed in the gut under the influence of gut microbes, which can then contribute to disease development. As a result, normalizing the gut microbiome can be an approach for disease intervention [R].
The Hygiene Hypothesis No Longer Stands
What we can take from all of this is that the hygiene hypothesis no longer stands. Strategies such as natural childbirth, breastfeeding, increased social exposure, less time spent indoors, proper diet with probiotics, and appropriate antibiotic use should be promoted in order to help maintain a healthy gut and subsequently lead to a balanced immune system [R].
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