Gut bugs affect DNA expression

Trillions of microbes - bacteria, fungi and viruses -  live in the human gut. They're known as your microbiome and they play a crucial role in keeping you healthy by helping the immune system, keeping bad bugs at bay and aiding digestion. Now scientists have discovered that they also influence the activity of some of our genes elsewhere in the body through what are called epigenetic effects. In essence, chemicals made by the microbes travel to many tissues and turn genes on and off. A diet rich in fruit and vegetables seems to encourage this to happen, while a western diet - that's also associated with poorer health and diabetes - blunts the effect. Kerstin Göpfrich heard how from discoverer John Denu...

John - When we consume food in our diet, if there's a fair amount of complex carbohydrates, which these bugs really like and they take this fuel and they convert it to small molecules that include things such as acetate, butyrate and propionate. These are small short chain fatty acids. So, for instance, acetate is essentially vinegar and so that gets absorbed by the host and is converted to information at the level of the epigenome.

Kerstin - That sounds very exciting - how did you find all this out?

John - We looked at and compared mice that were in a germ free environment so, basically, mice in a bubble versus those that are colonised and we compared the effect on the epigenome. One of the diets we looked is sort of a western type diet that has a much higher percentage of fat and simple sugars and we saw a real suppression of the effects on the host under a poor diet, so to speak. So the poor diet was suppressing this communication between our gut microbiome and the host epigenome so I think that's really an important finding.

Kerstin - How do your findings translate to humans? How would you test for that in a human being?

John - It's always tough to do such experiments in humans because it's hard to get people to eat what you want them to eat, right? There is evidence in humans that those molecules sort of individually, like acetate for instance, can have effects on humans. The question is are those effects going through the same mechanism that we've identified in the mouse? I suspect that they are, but that's for the future.

But I think it's quite interesting in our human history we use a lot of acetate, we use a lot of vinegar under conditions where we can't, for instance, grow fresh vegetables. For about 5,000 years, we've been pickling things. One could imagine that many of the ways in which vinegar perhaps mediates some of it's health benefits that have been describe, maybe it's through a similar mechanism as we've discovered in the mouse experiments.

Kerstin - So maybe there is a good reason why we put a pickled cucumber on our burger?

John - Absolutely. Yes that's right.

Kerstin - Indeed, John and his team saw similar epigenetic changes when they gave germ free mice some vinegar and the other fatty acids in their drinking water. And yet, John isn't advocating food supplements in order to reverse the effects of a crappy diet. There are lots of other health benefits to good food.

John - Maybe one way to summarise is to listen to your gut.