According to the FDA, foods must contain 5 grams of fiber in order to be called "high fiber." "But [nutrient-rich] foods that fall below this threshold are still good to include," says Moore.

A daily medium-sized apple—and its 4.4 grams of fiber—might keep the doctor away (at least according to the saying). But it can also get boring fast.

While some fiber-rich foods like nuts are high in calories, many others like popcorn aren't. “It will fill you up before it fills you out,” Blake says. “It displaces other calories.” ...

He says that our love affair with food additives — fiber, for example — can be traced back to a single moment in history: British navy, 1747.