Science Probes How Probiotic Yogurts Affect Your Gut

'Friendly' microbes might affect metabolism, but whether they're good for you is still unclear, researchers say

By Alan Mozes
HealthDay Reporter

WEDNESDAY, Oct. 26 (HealthDay News) -- Researchers have put the health promises of popular probiotic yogurts to the test and found they may alter the way in which food is metabolized.

But whether that means probiotic foods and supplements can improve your health remains to be seen, they said.

"Federal regulatory agencies are increasingly interested in evaluating all the health claims being made by probiotic food manufacturers," said study co-author Dr. Jeffrey Gordon, a biologist and director of the Center for Genome Sciences at Washington University School of Medicine, in St. Louis. "So what we did was try to develop a model for the human gut that can give us a way to measure the effects."

What they saw, Gordon said, "is that adding a few billion of these microbial organisms to a gut community already containing tens of trillions of bacteria can, in fact, influence the metabolism of food ingredients. The structure of the microbe community doesn't change. But the function does."

Funding for the research came from the U.S. National Institutes of Health (NIH) and Danone Research, an arm of the food conglomerate that makes Dannon probiotic yogurt Activia.

The study is published in the Oct. 26 issue of Science Translational Medicine.

The microbial communities found in all human beings are enormously bountiful, the authors said, and efforts have long been under way to better understand how humans and their resident microbe population interact.

According to the NIH's National Center for Complementary and Alternative Medicine, the term "probiotics" commonly refers to digestible live microorganisms, such as bacteria, viruses and yeasts, that have the potential to boost health when consumed in sufficient quantities.

In most cases, edible probiotics contain the same sort of "friendly bacteria" already found in the guts of most individuals. Makers of probiotic supplements claim they help fight disease by boosting the immune system, protecting against "bad bacteria" and aiding in the digestive process.

And some preliminary evidence does indicate that consuming probiotics may aid in the treatment of diarrhea, irritable bowel syndrome, bladder cancer, urinary and intestinal tract infections, and even eczema.

To explore whether the promises are backed up by hard science, Gordon and his associates set out to conduct a high-tech investigation involving mice and human twins.

In the first instance, germ-free mice were carefully raised so that the environment of their guts mimicked that of humans. In effect, the mouse guts played host solely to 15 human gut microbes, all of which had been genetically sequenced.

Next, seven sets of healthy, young-adult female twins were recruited.

Over four months, the "humanized" mice and the twins consumed a commercially available probiotic-cultured yogurt. The researchers analyzed bacterial gut composition and behavior patterns before, during and after probiotic consumption.

The result: The bacterial species in the yogurt did not take up fresh residence in either the human or animal consumers. Thus, the bacterial environment found in the guts of both mouse and man was roughly the same before and after yogurt consumption.

However, a subsequent urine analysis among the "humanized" mice unearthed "significant changes" in the activity of enzymes involved in metabolism, the team said.

The most prominent changes, the team further noted, had to do with the breakdown of carbohydrates.

But they concluded that more research is needed before anything definitive can be said about the effect of probiotic consumption on human health.

Still, they noted a silver lining. "We have successfully developed a way to test the effects of these microbes on the gut," noted Gordon. "And that means that we can now use this testing pipeline as we move forward, in order to get a better handle on the claims of various products already available in supermarkets."

Justin Sonnenburg, an assistant professor of microbiology and immunology at Stanford University School of Medicine, in California, lauded the study as "interesting, subtle and incredibly well-designed."

"The fact that they found that a probiotic preparation doesn't do incredibly profound things to your existing gut composition, but instead impacts its function, is a theme that is coming up over and over again," he said. "And that is, that it matters less what microbes are actually there, and more what they are actually doing."

Based on this work, it can be said that that consuming a probiotic will likely have some impact on the function of your gut microbial community, he noted. But, "it's still way too preliminary to say whether this means that probiotics are good or bad," he said.

More information

For more on probiotics, visit the U.S. National Center for Complementary and Alternative Medicine.

SOURCES: Jeffrey I. Gordon, M.D., biologist and director, Center for Genome Sciences & Systems Biology, Washington University School of Medicine, St. Louis, Mo.; Justin Sonnenburg, Ph.D., assistant professor, microbiology and immunology, school of medicine, Stanford University, Stanford, Calif.; Oct. 26, 2011, Science Translational Medicine

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