THURSDAY, April 21 (HealthDay News) -- Just like eye color or blood type, the bacteria that flourish in the gut can also be used to categorize humans, new research finds.

European researchers have determined that there are three distinct types of microscopic ecosystems that exist in the human intestine. What differentiates each type is which species of microbes are present and which are the most abundant, researchers said.

Although there's far more to learn about what those microbes do, researchers say your bacterial type may tell a whole lot about you, including how you metabolize food, how you synthesize vitamins and how you might respond to certain medications.

"We think humans can be categorized based on the micro-composition in their gut," said study co-author Manimozhiyan Arumugam, a research scientist at the European Molecular Biology Laboratory in Heidelberg, Germany. "We also have reasons to believe these are not specific to any continent, country, ethnicity or any other obvious factor."

The human gut is host to an estimated 500 to 1,000 species of bacteria, Arumugam said. Those species compete and cooperate with each other in microscopic ecosystems that remain relatively stable in a balanced, symbiotic relationship with the host -- the human body.

"They are not working alone, they have to work as a community," Arumugam said. "And they have to adapt to the host, such as what we eat."

In the study, published in the April 20 issue of Nature, researchers took stool samples of 22 people from four European countries (Denmark, France, Italy and Spain), extracted the DNA and determined which species of bacteria resided there. They combined their data with the results of earlier data on the gut microbes of 13 people from Japan and two Americans. They then added data from another 85 Danish people and 154 Americans.

Their analysis showed that the microbiota could be grouped into three categories. People with type 1, for example, had high levels of the bacteria Bacteroides. In type 2, Bacteroides levels were lower, but the Prevotella was prevalent. Ruminococcus was a big factor in the third enterotype.

"In the data sets we looked at, we found three types. Would it remain only three if you sampled 100,000 people? We don't know," Arumugam said. "It could also be that maybe these enterotypes could be refined more and that there are subtypes."

Since researchers began to understand that gut microbes play a significant -- and underestimated -- role in human health, one question that's been vexing the field is just how many versions of intestinal microbiota there are, said Justin Sonnenburg, an assistant professor of microbiology and immunology at Stanford University School of Medicine.

If there were an infinite number of variations, then using the information in the real world would be impossibly complex, Sonnenburg added.

"There's been this increasing realization over the past several years that the microbes that live in and upon us are wired into many facets of our biology, and it's also becoming clear that these microbes are going to be a major determinant of variation between individuals, both in relationship to our health, predisposition to disease, progression of diseases and how they should be treated therapeutically," he said.

But by identifying the three types, the new research represents a significant breakthrough, he added.

"This paper really makes a huge leap in establishing that this variation is not a continual and infinite, but that there these finite enterotypes," Sonnenburg said.

Think of it like eye color, Sonnenberg added. There's brown, green, blue, hazel and a perhaps a few other variations, but there is no purple, chartreuse or other colors.

The researchers said they had found no evidence that such characteristics as age, gender or body weight correlated to the gut microbe types.

However, looking across the entire sample, age, gender and body weight did correlate with certain genetic markers in the bacteria, hinting that it may be possible to eventually use such information to diagnose disease or determine who is likely to get diseases, Arumugam said.

More information

The U.S. National Institutes of Health has more on human microbiota.