So we just finished explaining how the gut is our second brain. How to top that? How about this: Your gut is its own planet.

The human intestine hosts an entire civilization of microorganisms – about 100 trillion by most estimates. That’s many times more than there are cells in your body. You may think you’re the center of your own universe, but in a sense you’re just a walking ecosystem for this teeming population of bugs.

The good news is, most of them are beneficial to us. Our intestinal flora help us digest food, excrete waste and even train our immune system. That is kind of old news, but only recently have scientists begun to uncover just how central a role our microscopic gut workforce plays in our overall health.

Here is one surprising connection – or rather, hypothesized connection: The gut flora may have a hand in breast cancer risk. Dr. Ece Mutlu of Rush University Medical Center is investigating this possibility. Click the “Listen to this story” button above to hear our interview with her.

It goes something like this: As the bacteria go through their little lives, eating and excreting, they produce many different compounds. Certain bugs are involved with hormones, specifically estrogen (listen to the interview to hear how Dr. Mutlu started thinking about this hint: it involves sewage treatment plants). Some bacteria break down estrogen, some activate it. Depending on what food we eat, we might encourage the growth of some bacteria or suppress others. That in turn could lead to higher levels of estrogen exposure, which is known to increase the risk of certain kinds of cancers (at least in some people).

This is still in the early stages of study. But it’s a hallmark of the new ways in which researchers are thinking about the gut flora. Science in general is good at identifying correlations (say, diet and cancer risk), but often less good at teasing out the mechanism behind it – the reason why some environmental factor influences a disease or condition. The gut bacteria are becoming prime candidates to make a lot of those links.

I, for one, am becoming a bit fanatic about this subject, so expect more down the line. Meanwhile, don’t forget to subscribe to our podcast (so you won’t miss out on cool interviews like Dr. Mutlu), follow us on Twitter, and find us on Facebook.