Gut types: Which of the three are you?

Which enterotype are you: Bacteroides, Prevotella, or Ruminococcus? Wait, you ask. What the heck is an enterotype? You’ve likely heard of blood types and may even know your own. Someday, you may also know about gut types. Researchers in an international consortium including Jeroen Raes of the Flanders Institute of Biology in Brussels, Belgium, have used human poop samples to classify people into three categories of enterotypes, or bacterial ecosystems.

Yes, you read that right. You’re an ecosystem. One of three possible types. Of all the DNA we carry around, about 1% of it is human. The other DNA belongs to the 100,000 billion microbes that hang out in our gut, among other places. Many are bacteria that take advantage of the protection and food we offer them while making vitamins or metabolites we might find handy. Yet even though these microbes number in the trillions, this research shows that they fall into only three distinct gut types, even fewer classifications than the familiar four blood types.

These classifications, or ecosystems, are the Bacteroides, Prevotella, and Ruminococcus, and they each seem to do things slightly differently. The Bacteroides ecosystem consists largely of bacteria that get energy by fermenting sugars and proteins. The Prevotella ecosystem contains a lot of microbes that like to dine on proteins in the mucusy lining of the gut. Mmmm. Ruminococcus, with its vague echo of cows, happens to be the most common. The residents of this ecosystem dine on those gut mucus proteins, but they also enjoy simple sugar treats. In addition to their different food preferences, these enterotype groups also have different output profiles. The Bacteroides type makes quite a few vitamins, including C and H, while Prevotella is good at making folic acid and vitamin B1.

You might think that where you live has something to do with which ecosystem you are. Nope. The researchers found that ecosystem distribution had little to do with continent of origin. The first 22 fecal samples they analyzed were European, and they fell into the three categories. When the scientists expanded their search to bacterial profiles from other continents, they found the same distribution of three profiles, although people from Japan were slightly more likely to be Bacteroides overall.

Are you what you eat, bacterial ecosystem-wise? Nope again, say the researchers, saying that a role for nutritional habits is unlikely. What you might instead be is what you host: while the enterotypes weren’t specifically associated with host traits like a high body mass index, some properties of specific bacteria were linked to these characteristics. In the case of weight, two types of bacterial pathways involved in fast use of energy showed a link to a high body mass index.

This latest on the invisible world you host comes to us thanks to an emerging field of science called metagenomics, or “beyond the genome.” Gut bacteria are notoriously finicky about growing in culture dishes. Add in that whole “number in the trillions” factor, and they’ve always been tough to tease out and identify. But now, scientists can sequence entire genomes. Researchers can take DNA from poop samples, get the sequences, and match those up to known databases of bacteria to figure out who’s living in whom.

Why bother? Your gut type or enterotype may someday tell a health professional more about you and how to treat you than even your own genetic profile. After all, your genes are only 1% of what you’re carrying around.

Maybe collecting poop samples and sequencing DNA isn’t your idea of fun. But for scientists like Jeroen Raes and his colleagues, who published their work in the April 20, 2011, issue of the journal Nature, it’s fascinating research that has led them to coin a new term – enterotypes – and to a new classification system for people: Bacteroides, Prevotella, or Ruminococcus. I wonder which one I am.

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