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Originally published February 5, 2012 at 7:03 PM | Page modified February 6, 2012 at 7:59 AM

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Medical: Digestive microbes work differently in fat, lean

University of Washington researchers find important bacteria information.

Scripps Howard News Service

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For the first time, scientists have studied the vast array of microbes found in the human digestive tract as one biological system — almost a stomach within a stomach.

Researchers from the University of Washington found that these complex gut colonies of bacteria organize themselves differently in people who are fat and those who are lean.

Scientists know that at least some of the 500 different species of gut bacteria in the average host play important roles in our digestive health, nutrition levels and even immune function.

A number of recent studies in animals and people have shown that heavier individuals are likely to have greater concentrations of bacteria that are more efficient at pulling energy from food. Other researchers have found little or no difference in the makeup of the little digestive helpers from person to person.

The difference may lay not so much in numbers as in how the microbes interact, the work by the scientists at Washington indicates.

By looking at the microbes as a "supra-organism"in which genes from multiple species collaborate, they were able to identify the different patterns. It's a huge undertaking because there are tens of trillions of microbes inside the gut, well more than the 10 trillion cells that make up the human body. And all those bacteria encode about 150 times more genes than are contained in the entire human genome.

In particular, the group was able to estimate changes in the abundance of different enzymes associated with humans who are obese, lean or suffering from inflammatory bowel disease.

They noticed that most of the enzyme differences were in areas that were not part of the main metabolic function of the microbes, but more on the edge of the system.

Elhanan Borenstein, the assistant professor of genome sciences who led the study, said that suggests those fringe microbes are reacting to environmental changes in the gut.

Microbes at the edges adjust to either harness energy sources that the gut normally doesn't process or release products that aren't used by the microbes — either way, affecting weight.

But that finding doesn't yet resolve the central question about our microbes — do they make us fat or do they change how they behave because we are fat?

Other studies have already shown that it's possible to manipulate, even transplant, gut microbes to help ease certain digestive disorders. It's not clear if the processes involved in obesity or bowel disease could be blocked or reprogrammed, but having a clearer picture of how they work together improves the odds they could be.

The research was reported in January in the Proceedings of the National Academy of Sciences.

(Contact Lee Bowman at bowmanl@shns.com.)

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