Scientists have discovered new clues about how microbes in our digestive systems may affect health.
European researchers found that the less diverse those microbes are, the more likely people are to gain weight, become obese and develop risk factors for serious health problems.
Evidence has been mounting in recent years that bacteria and other organisms in our bodies do a lot more than just help us digest food.
"We had kind of a notion that all these bacteria that live in our body will be important for health and disease," says S. Dusko Erhlich of the National Institute for Agricultural Research in France, who led the new research. But exactly how they're important has been a little fuzzy.
So Ehrlich and his colleagues conducted a detailed analysis of the microbes in the guts of nearly 292 Danish people. There were 169 obese people in the group and 123 who were lean.
For starters, as the scientists report in this week's issue of the journal Nature, the results confirmed earlier findings.
"The lean people had higher microbial diversity than the obese people," Ehrlich says. By more diversity, he means that the leaner folks had more intestinal bacteria — 40 percent more — and many more species of bacteria than the people who were fatter.
When looking just at the obese people in the study, the scientists found the people with the least bacterial diversity were likelier than those with a greater variety of microbes to keep gaining weight during the nine years the researchers kept track.
Perhaps even more surprising and important: People who had less microbial diversity — whatever their weight — were more likely to have a variety of risk factors for Type 2 diabetes, heart disease and cancer. Those risk factors included insulin resistance and inflammation.
"Even lean people who are poor in bacterial species have a higher risk of developing these pathologies," Ehrlich says.
All this supports the ideas that eating a poor diet or taking lots of antibiotics may be factors in the obesity epidemic and associated health problems, in part, because of the way they affect our gut microbes, Ehrlich says.
In fact, the researchers found evidence to support the role of diet in a second paper being published in the same issue of Nature. When they put 49 French people who were overweight or obese on a low-calorie diet for six weeks, the variety of the volunteers' intestinal microbes became much richer.
"That gives hope that we can not only diagnose the risk but do something about it — intervene to alleviate the risk," Ehrlich says.
Microbiologist Ronald Evans of the Salk Institute in California, who wrote an article accompanying the studies, agrees. "It shows that [even] if you are on the unhealthy side, with dietary intervention you can actually convert yourself back to the healthy side," Evans says. "This bad state is reversible in a relatively simple way, which is diet."
The researchers also identified eight species of bacteria that appeared to be missing among the people whose microbes were depleted, raising the possibility of someday creating a probiotic that could help.
"It's very possible to make a brew that is the collection of the [richly diverse bacterial] 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 the healthy state," Evans says.
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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. Transcript provided by NPR, Copyright NPR.