<aside> <img src="/icons/light-bulb_blue.svg" alt="/icons/light-bulb_blue.svg" width="40px" /> A whopping 70-80% of your immune system resides in the lining of your gut that is 1 cell thick, and the gut microbiome and your immune system work in harmony with one another.

The gut microbes help to regulate your immune system, and your immune system helps your body form a healthy balance of microbes.

“What’s present in the gut determines what education immune cells get." - David Herber, MD, PhD, professor at UCLA Health.

So to summarise, your gut health plays an important role in your immune system.

Another angle to consider is the immune response caused by damage to the lining of your gut.

To keep it simple: Gut dysbiosis (an imbalance of good and bad bacteria) makes holes in the gut wall (the epithelial layer that's one cell thick) by breaking the "tight junctions" that hold it together and things seep through that shouldn't = an immune response.

This damage is otherwise known as leaky gut, or increased intestinal permeability.

Now what breaks through is called bacterial endotoxin, and this activates the immune system and results in inflammation.

But what about hormones?

Hormones are typically produced by the endocrine system, which includes the following group of glands and the pancreas: pituitary, pineal, thymus, thyroid, and adrenal.

Your gut microbiome also produces hormones and sends signals to the glands in your body that dictate how much of each specific hormone you release.

These includes your thyroid hormones (more below), estrogen, serotonin, and more.

This is why gut dysbiosis (an imbalance of good and bad bacteria) can lower the levels of thyroid hormones T3 and T4, which can lead to what's called hypothyroidism (where your thyroid gland doesn't produce enough hormones).

Symptoms include "tiredness, weight gain, dry skin, cold intolerance, constipation, muscle weakness, puffiness around the eyes, hoarse voice, and poor memory.". (study)

So much like our immune system, that ecosystem of microbes in your gut affect your hormonal balance.

Who'd have thought what many see as just our "stomach" had such a widespread influence...

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