Before we start, just a warning to those of a sensitive disposition: this article is about poo. Not just any old poo either – human poo.

It won’t have escaped your attention that one of the hot health topics in recent years has been the health of the human gut. And specifically, the health of the gut microbiome – the huge and diverse population of bacteria and other microbes that lives in our intestines. Basically, healthier people have healthier gut microbes, and there’s no shortage of advice on how to improve gut health, which all comes down in the end to one thing: fibre, the more the better.

But here’s the thing: where do all these gut microbes come from? Historically, the answer to that question would have been obvious: early humans, through hunting, gathering and primitive farming, would have been exposed to microbes on plants and in soil on a daily basis. But where do modern humans get their gut microbes from?

To try to answer that question, researchers at the University of Illinois Urbana-Champaign have looked at one obvious suspect: gardening. They compared faecal samples from ‘gardening families’ (i.e. families with at least one serious gardener) with those from families who didn’t garden at all. For the gardeners, they also looked at the bugs living in their garden soil.

The results were clear: gardeners’ gut microbiomes were more diverse than those of non-gardeners. Not just the main gardener either, the whole family had more interesting gut microbes. As is often the case whenever you look at bacteria, some of the microbes couldn’t be identified, and gardeners had more of those too.

Now, you’re probably thinking that there’s a potential problem here, because gardeners and non-gardeners probably differ in all kinds of ways. For example, the researchers looked at their diets and found that the gardeners had diets richer in vitamins and fibre, at least partly from eating the products of their gardening. Maybe the gardeners’ richer gut microbiome is just a reflection of a healthier diet?