Bacteria in western theme. The good, the bad, the slacker.

The gut microbiome: The good, the bad, and the slacker (Part 1)

This is a simple warm-up preparing you for a series of upcoming posts dealing with the gut microbiome. You know, these microorganisms living inside you that can alter your mood, weight, and overall health.  

Remember the germophobic times? The times when germs were everywhere, and they were out to get you? Girls had germs that were incompatible with boys and vice versa. Your parents would take your sweet, strawberry ice cream away from you after you’d picked it up from the ground. And that’s even though you’d strictly followed the bulletproof “5-second rule” and, to be safe, also blew on it two or three times to rid it of the last pieces of germs. It’s called sanitizing, mom!

Germs, bacteria, microbes. We all eventually developed a red-alert state of mind toward these invisible suckers. Well, most of us did. Some embraced the dirty lifestyle, and the rest of us have suffered because of that.

Anyways, I’ve got news for you: germs are not all that bad. In fact, they are crucial for your life and physically make up a big part of you. They form your microbiome. The microorganisms that influence your food digestion, hormonal balance, mood and habits, immune system, body weight, and overall health.

What’s the gut microbiome?

The microbiome is an ecosystem in your digestive tract. A common society integrating bacteria, viruses, yeasts, and other microorganisms. They share your digestive area just like different species share our planet. Pretty cheesy, I know. But you like that hippie stuff, don’t you?

Not impressed yet? Let me solve that through some common points usually made about the microbiome:

Your body’s digestive tract consists of 10-100 trillion of these microorganisms.

That’s 90% of the cells in your body.

Roughly, that’s a mass of 2 kg (4.4 lbs).

That’s more than the weight of your brain.

And finally, many consider it a body organ in itself. Just like the heart or the lungs, your microbiome could be considered a body part.


There are three main types of microorganisms living in your digestive tract:

Commensal – The microorganism lives in the host, but it doesn’t do any harm or any good to it. It’s there, living well. Think of the 30-year-old that won’t move from home because he can’t afford rent in the open market and avocado toasts are so expensive. That damn economy! And such convenience…

Pathogenic – The microorganism harms the host.

Symbiotic – Both the host and the microorganism contribute to each other. A you-scratch-my-back-and-I-scratch-yours-type of relationship.

It’s the symbiotic type of bacteria that has received most of the attention because of the way it can influence our body functions, altering both your physical and mental traits. That’s all fine and dandy, but how do they do this?

How is the microbiome crucial for your health?

Lately, scientists have realized the impact of the microbiome on our lives. Especially three body functions have been linked to the microbiome. I’m talking about the immune system, the endocrine (hormonal) system, and the all-mighty metabolic system.

The immune system

Simply speaking, intestinal bacteria can communicate with the immune system in our body. It can signal the immune cells not to kill the “good” symbiotic bacteria or activate them against “bad” pathogenic bacteria.

There are other ways that the microbiome influences the immune cells. It’s known that bacteria are transferred from mother to offspring during birth. This is called a vertical transfer and initiates the offspring’s immune system. The commensal “slacker” bacteria have a role here, occupying space from the “bad” bacteria.

The metabolic system

We feed our gut bacteria every time we eat. They thrive on it. However, we get something out of it too. An unbalanced microbiome composition, for example, has been correlated with weight gain. Different bacterial strains could explain this. Some are more or less capable of extracting energy from certain foods.

The endocrine system

Hormones and hormonal balance are essential for many functions of your body. Mood, hair growth, muscle building, menstruation, energy, and metabolism, among others, are all influenced by hormones. Hormone levels could explain why your awkward colleague is constantly moody and depressed. Or their life might just suck. Which likely would have altered hormone levels as a consequence.

It’s possible that bacteria can control your hormonal system. One way they do this is to indirectly manipulate the levels of your “happy hormone,” serotonin, by controlling the metabolism of tryptophan, a serotonin precursor. As you can see, the hormonal and metabolic systems go hand in hand, and the microbiome could be seen as the handcuffs.

The microbiome can affect stress levels as well by controlling the magnificently named hypothalamic-pituitary-adrenal axis, the intersection between the hypothalamus, the pituitary gland, and the adrenal gland. These control stress, the immune system, and metabolism. Yet another circuit connecting everything.

Why do gut bacteria do all these things?

Well, it makes sense. The relationship between bacteria and hosts has been developed through evolution. It’s the survival of the fittest situation, where the bacteria do all they can to survive. Think about it; they tell the immune cells to protect themselves and kill pathogens. This is both good for them and the host. They help the host to digest and, in return, get nutrition out of it. They regulate hormone-signaling to the brain, telling it to get more of the food they like so the bacteria can metabolize it, then regulate the immune cells, and so on. You get the idea; the circle closed once again.

It’s a win-win, making everybody happy. But you better watch out. This circle could backfire on you as well. The truth is that it’s not all peace and harmony in your gut. Microorganisms in your gut compete constantly. You know how they say that you are what you eat? Your bacteria are also what you eat. You start giving those cute little things junk, and the junk-loving bacteria will thrive and grow. These bacteria can, in turn, start cravings for more junk by signaling to your brain for just that: “We gutz to have junk!”. This can turn into a vicious cycle, and it can take time to correct. This is called dysbiosis: an unhealthy microbiome

I heard somewhere that the microbiome is like a garden. I guess you have to be careful with what you plant and how you maintain that garden.

What now?

You see, germs are not that bad after all. Maybe licking the stop button on the bus as a kid (or on your way to work today) was not such a bad idea after all. On the other hand, maybe it was a terrible idea, and you should see a doctor. Stop licking buttons!

Anyways, this was a warm-up for the upcoming parts. We’ve covered a lot already, so that’s it for now. Digest it (get it?). I’ll be answering more of my microbiome-related questions soon. You’re more than welcome to ask or comment as well. I’ll do my best to answer them.

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