MICHEL MARTIN, HOST:
Scientists have known for a while that there are a lot of microscopic things living inside our guts, and they also know that these organisms hold enormous potential to improve our health. But researchers are still wrestling with some big questions, like how do you tell a healthy gut from an unhealthy one? New research in the journal Science points toward one way. NPR's Will Stone reports.
WILL STONE, BYLINE: Envision a vast ecosystem in your gut. To gauge how well it's doing, you can look at the microbes there and how diverse they are. But Dr. Martin Blaser says that's only part of the story.
MARTIN BLASER: There are some communities that are very unhealthy where the diversity is higher. Low diversity is not a universal marker.
STONE: Blaser directs the Rutgers University Microbiome Program. In search of a more reliable marker, Blaser and a team looked to the field of ecology and applied those principles to the gut.
BLASER: We found something that at first seemed surprising.
STONE: That a healthy microbiome has lots of competition. These bugs are all going after the same food. In an unhealthy gut, on the other hand, you see tight cooperation - microorganisms are helping each other out. Or, as Blaser puts it...
BLASER: What happens is that a little mafia takes control. They're cooperating with each other. They have a very cozy little deal and they're crowding everybody out.
STONE: In the study, the research team tested their model on several conditions - inflammatory bowel disease, colon cancer and a bacterial infection called C. diff. Each time, they saw this pattern. Andy Goodman directs the Yale Microbial Sciences Institute.
ANDY GOODMAN: This is an important and exciting study. We've been looking for a long time for general rules that allow us to interpret the microbiome across diseases.
STONE: He says the study is a meaningful step in that direction.
GOODMAN: One thing that is not clear is whether this alteration in the balance of microbial activities is a cause or a consequence of disease.
STONE: That would matter down the line if patients use this to suss out their own gut health - for example, through a stool sample. At this point, though, it's a tool for researchers. Kat Coyte is a scientist at the University of Manchester who focuses on the microbiome. She says it remains to be seen if the findings hold up in other diseases. Her lab works on the infant microbiome, which she says does rely on microbial cooperation, but she says, eventually, the dynamic seems to shift.
KAT COYTE: Probably, at least in health, the majority of interactions are competitive 'cause you just simply can't maintain a nice, friendly ecosystem. It's ecologically unstable. It's evolutionarily unstable.
STONE: There's so much hype around the gut microbiome these days, and marketing of products and tests that are way ahead of the evidence. Coyte says people should think of it like the Amazon rainforest, with its web of relationships and organisms.
COYTE: The problem is, we're trying to look for, like, one perfect measure of good versus bad, and the fact is that there won't be one perfect measure.
STONE: In fact, she says it's quite possible in some cases that what's bad for my microbiome is good for yours.
Will Stone, NPR News.
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