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Developed digestion proves people more microbe than man


Medical anatomical model

Last time, I talked about the strange case of a woman who was dying from a nasty infection in her bowel, how after eight months she had lost 27 kilograms of weight and was confined to a wheelchair because of her weakness.

She was also having to wear nappies, because of her continual diarrhoea, and was just weeks away from dying. And then I discussed how a transfusion of faeces from her husband had magically 'reset' the microbes in her gut, and how she came back from the almost-dead.

So what are these mysterious microbes in the gut? (Now I did discuss this first about two years ago, but a lot has happened since then, so this is the update.)

The first thing to realise is that your body is made of cells. Ten per cent are human, but 90 per cent are microbes. In fact, if an alien looked at you, they would see you as being just a carrier for the other life forms that make up 90 per cent of the cells in your body.

We are never alone, from when we are born, to after we die when they help recycle us.

Yep, it's true! We humans are mostly made from other life forms. We are a super-organism, a blending of us and them. (Please note: I am talking about the numbers of cells, not their mass or weight.)

Only about 10 per cent of the cells in your body came from that single fertilised egg that was made when your mother and father loved each other very much in a very special way.

These add up to about 1–10 trillion cells. The other 90 per cent of the cells in your body (10–100 trillion) belong to other living creatures, mostly microbes.

The vast majority of these other living creatures are single-celled beasties, such as bacteria, living in your gut. In total, these microbes, and their little friends, weigh about 1.5 kilograms.

The reason that they weigh so little, even though there are so many of them, is that these microbial cells are much smaller than human cells.

The result is that each of us is a strange microbe-human hybrid. Yes, we are more microbe than man! (Or, because they mostly live in our gut, you can say that we are 10 per cent human and 90 per cent poo.)

We have a fair and reasonable relationship with them.

Every single time that we eat, they eat. They grab, store and redistribute energy from the food we put in front of them. They use this energy to maintain and repair themselves. They reproduce, and they communicate with each other.

But in return, they do stuff for us. They make vitamins for us, such as vitamin K, thiamine, pyroxidine. They protect us against nasty microbes. They help the immune system, associated with the lining of our gut, grow and mature.

In fact, they help our gut grow. They help the cells that line our gut grow and proliferate, and turn into different types of cells.

They also help make the tiny capillaries that line the outside of the gut and pick up the fats, proteins and carbohydrates from what we eat. Without them, our gut would be a tiny shrivelled version of its healthier robust microbe-laden self.

Microbes also break down carbohydrates that we cannot digest, and extract energy from them for us. For example, we humans have about 98 enzymes that break down carbohydrates.

But the bacteria in our gut have over 240 enzymes to turn carbohydrates into energy. These extra microbe enzymes can break down sugars that our human enzymes cannot.

Some of the energy goes to the microbes, but the rest goes to us. In fact, if it wasn't for the single-celled creatures in our gut, we'd all be a lot thinner.

In one study, mice were delivered by Caesarean section in sterile conditions, so they had no bacteria living in their gut.

The mice were then raised in sterile environments, and fed only sterile food. Compared to their regular, germ-laden siblings (who were fed the same food), these germ-free mice ate 29 per cent more and yet, were very skinny, carrying 42 per cent less fat.

And then, when their mice guts were colonised with the single-celled creatures of their regular siblings, they simultaneously ate less and got fatter.

So now that you have a bit of an understanding of these microbes that make up 90 per cent of the cells in your body, I'll stop, and next time, I'll tell you the story of an animal whose gut doesn't match its diet. Yep, the giant panda!

Tags: diseases-and-disorders, medical-procedures, stomach-and-digestion

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Published 27 April 2011

© 2015 Karl S. Kruszelnicki Pty Ltd