What is the part of plant food that you cant digest?

The part of plant food we can't digest is called dietary fiber, or roughage. It's the tough, stringy bits that make up the cell walls of plants.

Dietary fiber is an important part of a healthy diet, even though we can't digest it. It helps keep us feeling full, helps regulate our blood sugar levels, and helps to promote good digestion by bulking up stool and making it easier to pass.