Does the DNA of food survive digestion?

18 March 2014



Does the DNA of food survive the human digestive system?

Thank you

Alexander Hartley, Norwich, Connecticut, USA


Chris Smith answered this question...

Chris - This is very interesting because, originally, people thought the answer to this was no. But then, about 4 years ago, there was a lovely paper published in the journal Nature where scientists had been taking samples of seawater. They had studied the DNA of these seawater samples and they had found a combination of genes which encoded enzymes to break down a certain set of sugars in seaweed. They thought this was brand new - no one had discovered this before.

So, they had a look in the database of genes compiled from all over the world. And they were rather annoyed to see that someone had published a very similar DNA sequence previously and they thought, "Who's done that? That's annoying!"

But, then they found that these gene samples were all collected from people in Japan, and they all corresponded to samples taken from the intestines of these people. They realised what's happened is that people are eating sushi in Japan - because that's got seaweed in it - and the bacteria they were studying in the sea were eating seaweed; the people had eaten some seaweed and the DNA from the microbes in the seaweed had leached out into their intestines and those people's own intestinal bacteria had picked up the DNA and incorporated the genes into their own genomes.

This is as one person put it, rather like you going into a restaurant and someone equipping you with a brand new knife and fork to eat a rather tough steak with because if you see a sharper knife and fork, you think "I'll have that one instead of the blunt knife I've got already!"

So, yes, DNA can survive transit through the human digestive tract, and other organisms can actually incorporate it, which I think is absolutely stunning.

Richard - It's amazing, isn't it? I'm stunned that you look at the process of something passing through us and everything is sort of subjected to the acid and the attack by the body, and all the bacteria, and yet, DNA can survive that. That is incredible!


Where it says: "and those people's own intestinal bacteria had picked up the DNA and incorporated the genes into their own genomes."
Please clarify : Does this mean Into the intestinal bacterium's genome or into the person's genome?

Bacteria indulge in a process called horizontal gene transfer. They can acquire and assimilate pieces of exogenous DNA (DNA coming from the environment) and use it, adding it to their own genetic repertoire. This is likely to have been the case here.

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