Diversity is good for your gut — and red wine might help. In a pair of studies published Thursday in Science, researchers from Belgium and the Netherlands present the most comprehensive work on the human microbiome to date. After studying the poop of thousands of citizen volunteers, they've mapped out the species of bacteria that live inside their guts — and linked some of those bacteria to associated lifestyle factors.

Some scientists hope to use the microbes that live in our guts to diagnose and treat the diseases that seem to be linked to them. We still don't know what the "best" microbiome is, or even whether or not there's one "normal" microbiome. So we're going to have to wait a while longer for our perfect poop transplant therapies. But with the data presented in the two new studies, scientists take a big step toward understanding how our little passengers can make big changes in our lives.

The first study, led by Jeroen Raes of the Flanders Institute for Biotechnology, centers around the so-called Flemish Gut Flora Project, which collected stool samples from 3,500 volunteers. "Which is a lot, because Flanders only has a population of around 6 million, and we didn't pay any of these people. They were all just interested in the science," Raes told The Post. They've analyzed 1,100 samples so far and cross-checked their findings with a Dutch health monitoring program called LifeLines — which is the main data source for study No. 2, led by the University of Groningen's Cisca Wijmenga.

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"Maybe from an American perspective, Belgium and Holland are very close," Raes said with a laugh. "It’s true in terms of geographic distance, but genetically these groups are quite different, and diet habits are quite different as well."

Raes suspects that microbiomes, which are heavily influenced by diet, may be quite different in countries outside the Western world. But he thinks the results of the two studies will probably be fairly applicable to other populations in Europe, and perhaps in America as well.

Raes and his colleagues were able to use the Dutch data to confirm 92 percent of the 69 influential factors they identified in Belgium, which bodes well for the accuracy of the testing. But even though the countries are just about as far apart as New York and D.C., they found marked differences.

"In Belgium we found associations with beer and chocolate, while in the Dutch population we saw associations with dairy products," he said. "We were very excited to see that, because that's a very important dietary distinction — we like our chocolate. They like their milk."

Indeed, both studies found even small dietary changes to have a big effect. In Wijmenga's study, while some dairy products, such as yogurt and buttermilk, increased the diversity of species in the gut, full-fat products tended to decrease that diversity. Red wine and coffee seemed to increase the biodiversity of the gut as well. High-calorie, carb-heavy diets had the opposite effect. Surprisingly, babies didn't seem to be influenced by breast feeding (or delivery method) at least inside their gut.

"In total we found 60 dietary factors that influence the diversity. What these mean exactly is still hard to say," Alexandra Zhernakova of the University Medical Center Groningen, the first author of the Science article, said in a statement. "But there is a good correlation between diversity and health: greater diversity is better."

It's always nice to hear there might be a good reason to enjoy chocolate and wine — in moderation, of course. But some of the results may be tougher to swallow: Zhernakova and her colleagues also noted 19 different medications, some of them very commonly used, that seem to negatively impact gut diversity.

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It wasn't surprising that antibiotics stifled bacterial diversity, nor were scientists surprised to see an effect from laxatives. But antihistamines, hormones and anti-inflammatory drugs were implicated as well. Raes and his team identified many of the same drug associations.

That doesn't mean you should scarf down chocolate and swear off allergy medication in the name of a better gut.

"For now, these are really just associations," Raes said. "We don't really know the cause or consequence of them. It's my opinion that the best science gives more questions than answers, and these 69 factors we found are really just a new list of questions to answer."

Even those factors only actually accounted for a small percentage of the species variation they observed. Most of the variation from one gut to another is still totally unexplained. It could have to do with as-yet-unidentified lifestyle factors, but genetics probably plays a large role as well.

In any case, while diversity did seem to be linked to overall health, the researchers still aren't sure that there's one way — or even a dozen different ways — that a gut microbiome should look.

"Maybe there is not one perfect gut microbe composition," Raes said, adding that he was frustrated not to have identified a perfect gut. He hopes that the analysis of the rest of his country's volunteers will help, and that studies as comprehensive as these will soon crop up around the globe to add to the available data.

"These studies and others out there like them are showing a certain maturation of the field," he said. "The field has been extremely excited and rushing forward with lots of hype, but at the same time we need to sometimes sit down and work on the basics, and this type of research will help us to do better when studying diseases and trying to produce diagnostics and drugs from the microbiome."

"It’s sort of a young field growing up, and this shows that," he said.