Overselling the Microbiome (Body Eclectic Part 4)
Posted by Richard Conniff on April 23, 2013
When a scientific team recently suggested that changes in gut bacteria could protect against stroke, Jonathan Eisen of the University of California at Davis lambasted them for “absurd, dangerous, self-serving claims that completely confuse the issue of correlation versus causation.” Eisen, a specialist in microbial genomics, now regularly presents “overselling the microbiome” awards on his blog. He says he doesn’t doubt the ultimate importance of the microbiome: “I believe the community of microbes that live in and on us is going to be shown to have major influences.” But believing that “is different from actually showing it, and showing it doesn’t mean that we have any idea what to do to treat it. There is danger here.”
For instance, probiotics, dietary supplements containing live bacteria, are generally harmless. Most contain the same microbes people have been consuming more or less forever. But exaggerated reports about beneficial microbes may lead people to regard the supplements as a cure-all, warns Richard Sharp, a bioethicist at the Cleveland Clinic. Manufacturers are careful not to claim specific health benefits because that would force them to undertake the kind of safety and effectiveness tests required for drugs. “But if somebody says they have a cure for everything,” says Rob Knight, “it’s probably a cure for nothing.” Still, U.S. probiotic sales were up 22 percent last year.
Researchers say they are only beginning to realize how subtle the interactions among our microbial species can be. They hope ultimately to develop probiotics that are correspondingly precise. But in the meantime, if the microbiome is like a symphony, then adding in current probiotics may be the equivalent of performing the piano solo with your elbows.
In certain rare circumstances, hitting the wrong notes may prove deadly. Administering probiotics before treatment seemed to make sense to the physicians in one study of severe acute pancreatitis, a bacterial inflammation of the pancreas. The theory, says the lead author, a Dutch gastroenterologist named Marc Besselink, was that a dose of beneficial microbes might crowd out dangerous microbes. That kind of “competitive exclusion” has worked well in some other conditions. But the pancreatitis patients receiving probiotics died more than twice as often as those who did not. The deaths occurred only in the most severe cases, where organ failure was already underway, and there was nothing to raise concern about the way most people use probiotics. But it was a wake-up call: The microbiome is a complicated system and we are only beginning to understand what happens when we tinker with it.