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Whole grains

Best

Whole grains, such as whole-wheat bread, oats, and brown rice, are a good source of fiber, which helps digestion.

"If there's one thing America lacks, it's fiber," Anderson says. "We need 20 to 30 grams a day and we maybe get 12."

Fiber also can help you feel full and lower cholesterol, but it can cause bloating, gas, and other problems in people who quickly ramp up their intake—it's better to take it slow when consuming more. And wheat grains are a no-no for those with celiac disease or gluten intolerance.

Next: Bananas