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Diet Determines Type of Gut Bacteria

Tom Avril

Posted Sept 7, 2011

Here's some new dietary research, if you have the stomach for it: Your choice of foods may affect the kinds of bugs that live in your intestines.

In a study of 98 people and their waste, University of Pennsylvania scientists reported Thursday that a person's long-term diet is connected to what kinds of bacteria live inside the gut.

The intestinal tracts of folks who typically ate a high-fat, high-protein diet tended to be dominated by one kind of bacteria, whereas those who favored carbohydrates and vegetables had more of another type. Moreover, a short-term alteration in diet yielded small changes in the person's bacterial community within just 24 hours.

The findings are part of a growing body of research into how the teeming tide of microbes inside the body plays an essential role in human health, and how it might be tweaked to address such ills as obesity, diabetes, and inflammatory bowel disease.

Some researchers have explored the use of probiotics, the dietary supplements that contain benign bacteria. For certain severe bowel disorders, physicians have even tried something called a fecal transplant -- putting healthier poo into the colon.

The Penn study, published online by the journal Science, looks at a much simpler idea: eating different foods.

It drew praise from George Weinstock, who is a genetics professor at Washington University in St. Louis and a leader of the ongoing Human Microbiome Project -- a microbial genome-sequencing project akin to the landmark government effort that sequenced the human genome.

"This is really interesting, tantalizing science," Weinstock said of the Penn study, in which he was not involved. "It's sort of like you have the carnivore gut and the herbivore gut."

Previous research had shown that people can be grouped into one of several broad categories by their intestinal bacteria. In 2010, one study found gut bacteria differences between children in Europe and rural Africa, who have a markedly different diet.

But the Penn study was much larger and explored the link to diet in extreme detail, with a statistical analysis of nearly 100 fats, amino acids, plant-derived compounds, and other nutrients that the study subjects reported consuming over the previous year.

"There were oceans of data," said Frederic D. Bushman, a microbiologist at Penn's Perelman School of Medicine.

Bushman led the study along with Penn gastroenterologists Gary D. Wu and James D. Lewis. They had help from colleagues at several other institutions, including gastroenterologist Robert Baldassano at the Children's Hospital of Philadelphia.

There was not a sharp boundary between the two major kinds of bacterial communities.

Yet a clear pattern emerged, with people on high protein-fat diets tending to have intestines with more of the bacteria called Bacteroides, and others having more microbes from the genus Prevotella.

The one vegan in the study and most, but not all, of self-described vegetarians fell into the latter bacterial group, Lewis said. Perhaps a few of them were sneaking the occasional hamburger?

The study also found that regular consumption of certain things, including red wine and aspartame, was linked to subtle changes in the gut bacteria.

The scientists did not assess whether it was more beneficial to host one kind of bacteria than the other; they recommended further study to find links between the bacterial category and disease.

The scientists also did not show that diet causes a person to fall into one bacterial category or another. In theory, the reality could be the other way around, with the type of gut bacteria leading people to prefer certain foods.

But the short-term portion of the diet study suggested that food does have an impact. Ten of the study subjects were sequestered in hospital rooms and fed controlled diets for 10 days -- some getting high-fat/low-fiber meals and others getting the reverse.

Genetic sequencing of their feces revealed that the composition of their intestinal microbes started to change, albeit slightly, within a day.

Whether a change in long-term diet could shift someone into a different bacterial category remains to be seen. The Penn researchers said one way to find out would be to analyze recent U.S. immigrants, some of whom adopt a Western diet, though such a study would have to account for all of the other changes in environment.

Other factors that seem to influence the composition of internal bacteria include two variables in babies: whether the birth is vaginal or cesarean, and whether the mother is breast-feeding. Chronic disease, excessive use of antibiotics, and a person's genetic makeup may also play a role in the composition of internal bugs, said Washington University's Weinstock.

Studying this microscopic universe is a complex undertaking, as the number of microbial cells in the body outnumbers the actual human cells by a factor of 10-1. And everyone is different.

"It's almost sort of like a fingerprint," Penn's Wu said.

It is a curious, mutually convenient relationship that has emerged over thousands of years between the tiny organisms and their flesh-and-blood hosts. Some of the intestinal microbes directly assist in digestion, for example, while others influence which human genes are "turned up or turned down," Lewis said.

Obesity is a subject of particular interest to bacteria researchers, because of the recent epidemic. Lewis said it was unlikely that microbes alone could explain the increase, given the increase in portion sizes and the decline in exercise. Still, he said there are hints that bacteria indeed play a role.

After all, the bugs are what we eat. Contact staff writer Tom Avril at 215-854-2430 or tavril@phillynews.com

©2011 The Philadelphia Inquirer

 
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