A primary limiting factor in the study of probiotics has been the disagreement about what constitutes a healthy gut. The understanding of the distribution of bacteria species in a healthy person's gut took a step forward recently when researchers announced they have discovered a way to classify people into three basic types based on their internal bacterial ecosystems.
In a paper published in the journal Nature researches laid out three so-called enterotypes—labeled types 1, 2 and 3—based on a characteristic distribution of species for each type. In Type 1 bacteria in the Bacteroides genus predominated, whereas in Type 2 the genus Prevotella was ascendant. The most numerous strains in Type 3 were less well characterized.
"We've suspected this kind of thing for a while. The tools haven’t been there until last five years to generate the kind of data that would let you actually see this kind of thing," said Andrew Benson, professor of microbiology at the University of Nebraska in Lincoln. "This is pretty cool and it’s pretty big."
Benson conducts his research in UNL’s Food Science and Technology Department. In a recent paper published in the Proceeds of the National Academy of Sciences, Benson and his coauthors investigated gut biota using mice as test subjects.
"One of the things we showed is that there are strong correlations between different groups of (gut) organisms, so if you find organism one you always find organism two. And we showed that one of those correlations is under genetic control by the host," he said.
Benson cautioned that the Nature paper, while important and exciting, is still somewhat preliminary. "It's still a pretty small sample set," he said. The research used data gathered from 39 subjects in Europe, Japan and North America. Benson's research typically uses data gathered from thousands of mice.
Mike Bush, vice president of business development for probiotics supplier Ganeden Biotech, sounded a cautionary note, too. "The gut microbiota is so complex and they haven't identified but a fraction (of the species)," he said. If you make the buckets big enough, you could put everyone into three of them, he added, paraphrasing another researcher.
The three enterotypes delineated by the researchers in the Nature paper, headed by Peer Bork of the European Molecular Biology Laboratory in Heidelberg, Germany, showed no ethnic or regional correlations, leading to the conclusion that these three divisions are determined at a more fundamental level, one largely independent of family heritage or habitual diet.
"What I'm interested in is how the host shapes the microbiota. Ultimately what we want to know is how the host does that genetically," Benson said. The immune system is involved in determining the microbiota, he said, but exactly how is not yet clear.
The different enterotypes discovered by Bork's group also correspond to slightly different performance of the digestive system. People who fell into the type 1 category synthesized more vitamin B7 (biotin), while type 2 subjects were better at synthesizing thiamine. Differences like these open the door for the holy grail of supplement science: finding a way backed by solid research to tailor a supplement suite, including probiotics and other supplements, to an individual patient.
"That is entirely possible. If you’ve got a type 1 microbiota there might be functions that are underrepresented that you need to now supplement in your diet, that would be different from what somebody with enterotype 2 would need," Benson said.
"It gives you a good direction to head in," Bush agreed.