By Melissa Pheterson

"The colon is not just an organ, it's an entire ecosystem," says Mark Liponis, M.D., author of UltraLongevity: The Seven Step Program for a Younger, Healthier You. Infinitesimally folded to produce food-absorbing surface area, the stretched-out gut would resemble a tissue paper large enough to blanket a tennis court. Trillions of bacteria (or "flora") slosh around — some playing nicer than others — and all playing a key role in your digestion, elimination and immunity. Recruit the "good guys" to work to your advantage by knowing five...

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