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Microbes, those little bacteria that live in our guts, are increasingly found to have a lot of influence over our health. Well, now European researchers have discovered the less diverse people's digestive systems are, the greater their risk for obesity and related illnesses.

As NPR's Rob Stein reports, the findings published in the journal Nature could lead to new ways to prevent could lead to new ways to prevent and treat some major public health problems.

ROB STEIN, BYLINE: Evidence has been mounting in recent years that microbes in our bodies - bacteria and other organisms - do a lot more than just help us digest food. Here's Dusko Ehrlich at the National Institute of Agricultural Research in France.

DUSKO EHRLICH: We had kind of a notion that all these bacteria that live in our body that they will be important for health and disease.

STEIN: But exactly how they're important has been fuzzy. So Ehrlich and his colleagues analyzed the microbes in the digestive systems of nearly 300 people in Denmark, and what they found stunned them.

EHRLICH: One quarter of people are poor in bacteria.

STEIN: Poor in bacteria meaning they not only have far fewer microbes in their guts. The diversity of the bacteria they have left is much lower. They're missing key species.

EHRLICH: And the difference is about 40 percent between the poor and the rich.

STEIN: And when they compared the bacterial haves to the bacterial have-nots, the scientists discovered this made a big difference to their health. The have-nots were more likely to be obese, more likely to continue to gain weight and more likely to be showing risk factors for all kinds of health problems, including diabetes, heart disease and cancer. And they found something even more surprising.

EHRLICH: What turned out to be very interesting is that even lean people who are poor in bacterial species have higher risk to develop these problems.

STEIN: Apparently because the microbes that are left tend to be the unhealthy kind. Now, all this supports the idea that lots of big health problems that we're having these days are connected to how we're disturbing the delicate balance of microbes in our bodies.

EHRLICH: Perhaps repeated exposure to antibiotics, which are toxic for bacteria, could lead to decrease of richness.

STEIN: Another possibility is what we eat these days. To take a look at that, the researchers conducted another study. They put 49 overweight French people on a low-calorie, low-fat, high-fiber diet and watched what happened to their microbes.

EHRLICH: The richness increased very significantly. That gives hope that we can do something about it, intervene to alleviate the risk.

STEIN: Intervene by simply eating better, according Ronald Evans of the Salk Institute in California.

RONALD EVANS: It shows that if you are on the unhealthy side, that with dietary intervention you can actually convert yourself back to the healthy side.

STEIN: The researchers also identified eight species of bacteria that appear to be missing in people with poor microbes. That raises the possibility of creating a probiotic to help them.

EVANS: It's very possible to make a brew that is the collection of the rich population, put that into a probiotic pill and give that to people who have the poor population and see if the good ones can take over and actually transmit a healthy state.

STEIN: Now, that sort of thing is easily years away. But the new research offers clues to how we might manipulate the microbes in our bodies to keep us healthy.

Rob Stein, NPR News.

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