Click here to read the full article. Prebiotics are the foods and/or supplements that help nourish healthy bacteria. They’re usually made up of fiber compounds that pass undigested through the GI tract. “They’re like dinner for the bacteria to dine on,” explains Raphael Kellman. The bacteria feast on the fibers by fermenting them, creating by-products that can help improve insulin sensitivity and protect against inflammation, he adds. Prebiotics include foods like asparagus, garlic, Jerusalem artichokes, jicama, leeks, onions, and radishes.