The bacteria living in our guts play in an active role is feeding us, whether it's breaking down nutrients our own stomachs can't handle, or synthesizing vitamins. Here's one more intriguing piece of the puzzle: a molecule excreted by the bacteria digesting fiber makes us feel more full.

If you've ever perused a diet book, you've seen fiber recommended because it's hard to digest and keeps you full. It may more to do with the sheer bulk of fiber alone. As scientists are increasingly coming to realize with all things digestion, the gut bacteria are involved, too. New Scientist explains:

A fatty acid called propionate is released when the bacteria in our gut digest fibre. Propionate makes people feel full by activating cells in the large intestine that produce the satiety hormones GLP-1 and PYY: these tell the brain that it's time to stop eating.

In a study published this week in the journal Gut, scientists turned the bacteria waste into a powdered form called inulin-propionate ester (IPE). Then they give it to overweight and healthy volunteers, who ended up eating 9 to 14 percent less, respectively, than controls who got ordinary fiber.

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"Bacteria waste" doesn't sound so bad when you realize it's basically the waste of bacteria that already live in our guts. We're still just beginning to unravel the workings of the gut microbiome, but it looks these little microbes play a big role in weight and obesity. [New Scientist, Gut]

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