It's tough to digest

FIBER

This dietary component keeps your gut healthy and is often found in whole grains, fruits, and vegetables. You might also call it "roughage.

The clue "It's tough to digest" plays on two meanings of "tough." Literally, fiber is hard for the body to break down, which is why it aids digestion. The wordplay also hints at "tough" as in difficult—since fiber resists easy digestion, it fits both interpretations neatly.