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There's no magic elixir for healthy aging, but there's one more thing to add to the list: good gut health. There's been an explosion of research lately with scientists learning more about the importance of beneficial bacteria that thrive in the digestive tract. As NPR's Allison Aubrey reports, a new study of older people finds eating a diet that helps maintain a diversity of bacteria is linked to better health.

ALLISON AUBREY, BYLINE: If you think about the human gut as a factory, the food we eat is sort of like the raw material. It helps determine what kinds of bacteria can thrive. And Professor Ilseung Cho of NYU School of Medicine says the more diverse the bacteria is in our guts, the better.

ILSEUNG CHO: So the idea of diversity in a bacterial community, or in the gut microbiome, is actually fairly important. And what we're only now beginning to realize is that there is a very close interaction between the bacteria within the GI tract and human health and disease.

AUBREY: He says beneficial bacteria do a lot for us. They help with digestion, help our bodies make vitamins, but they also have to compete with the harmful bacteria. That's why we want a variety of the good kind.

CHO: So if you have a lot of diversity and one bacteria that's doing something that's good is knocked out, then you might have other bacteria that can compensate for that loss.

AUBREY: Now, to get a handle on who might have diverse communities of gut bacteria, researchers at the University College Cork in Ireland decided to study a group of older folks. Some were living in nursing homes or assisted living. Others lived in their own homes. And lead author Paul O'Toole says what he found were big differences.

PAUL O'TOOLE: We were startled to be confronted with the observation that the kind of microbiota in your intestines depends on where you live.

AUBREY: If you lived at home, O'Toole says, you tended to have a rich diversity of bacteria. But those living in long-term care facilities had, by comparison, fairly impoverished communities of gut bacteria. Now, there may be many factors at play here, but O'Toole thinks one is key.

O'TOOLE: Well, what explains it is the diet, because uniquely, we're one of the few microbiota studies which has all this clinical data and also dietary habits.

AUBREY: O'Toole explains, at home, the seniors had fairly high-fiber diets. They ate fruits, vegetables, lean meats and fish. Their meals tended to vary and include a range of grains and proteins. By comparison, the diet in nursing homes had much less variety.

O'TOOLE: Mashed potato and porridge were the only staples in the diet type that were consumed daily.

AUBREY: There was also lots of sweetened tea, puddings and biscuits or cookies. O'Toole says that when you put this whole picture together, he saw that the people with the diverse microbiota also scored better on clinical tests gauging mobility, cognition and overall health, and the results were stronger than he expected.

O'TOOLE: I think we were surprised that the correlations between microbiota and health came out so strongly.

AUBREY: These findings, which are published in the journal Nature, are not proof that diverse microbiota are leading to better health. Physician Gary Wu of the University of Pennsylvania says as important and intriguing as this paper is, it establishes a link, not a cause.

GARY WU: Is it really that diet is altering the health of the individual through altering the gut microbiota? Or is it that people who are just not as well tend to be housed in long-term care facilities?

AUBREY: And their unhealthy guts are just another indicator of sickness. Wu says unraveling the cause and effect is what researchers will try to do in future studies. Allison Aubrey, NPR News.

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