Could identical twins have the same microbiome?

If they ate the same things, would their gut bugs be the same?
29 June 2021


Twin babies in bunny outfits.



If two identical twins ate identical food, would they have the same microbiome?


Microbiome geneticist Rob Finn, and bodyweight expert Giles Yeo stepped in to answer this question...

Rob - It's really hard to answer that because it depends how long they've been eating exactly the same diet for. Your microbiome changes over time. It's a bit like when you sort of plough a field, and you see the succession of plants that come in, and then it was left long enough, you'd eventually get trees. And so your microbiome is constantly changing. We also have to remember, we are carrying around two kilograms of microbes in us. So when we take two individuals, their microbiomes can really differ by 80%. So there's some really interesting sort of things at play there. However, I think that if they had been in a very confined environment, eating exactly the same diet, I think there's a good chance that their microbiomes would be close to identical as well. The only place I've ever seen this sort of thing happen, is people in hospitals when they had these very regimented shake diets, where they had three shakes every day for about a month and a half. And that is the only time when I've seen uniform microbiomes where it was really hard to tell them apart from two individuals.

Chris - Giles, you're nodding - we haven't really brought up the interface between where you're coming from with calories in food and how much energy we extract from our food, and where Rob's coming from with the microbiome that sees our dinner before we do.

Giles - So we know that the heritability - the percentage of variance of a given trait that's down to your genes versus the environment - the heritability of the microbiome is around 40%, I think roughly. So I think in the wild, twins would normally have around 40% of similar microbiome. That's my understanding. Now the role of the microbiome in terms of metabolising our food... I mean, huge. It's clearly going to be the first line. That's where our food gets to first. And there are a number of things that the microbiome in particular plays an important role in metabolising. And they're going to be soluble fibres. So normal fibre, the insoluble stuff, we eat it, it keeps the bugs happy and it comes out the other side, but the soluble fibre, so this is like pectin, the stuff that you make jam, or jelly for the Americans, and the bugs are able to ferment that into short chain fatty acids. The other thing which the bugs also play a role in terms of metabolising are going to be sugars. So I'm not talking here about sucrose, but polysaccharide - so long chains of sugars that are there. And some bugs will be able to ferment that and give off gas. So sometimes some sugars can make us get a bit gassy, and that's going to be down to the bugs that we've got.


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