Cellulose
Cellulose is the rigid, insoluble fiber that makes up plant cell walls, providing structure to stems and leaves while serving as a key source of dietary fiber.
Cellulose is a tough, insoluble polysaccharide that forms the primary structural component of plant cell walls. It consists of long chains of glucose molecules linked together and provides rigidity to stems, leaves, and roots. Found abundantly in wood, cotton, and agricultural crops, it is essential for plant growth and serves as a major source of dietary fiber.
What this means in real life
When you eat lettuce or celery, the crisp, crunchy texture comes from cellulose in the plant cell walls. Your body can't break it down for energy, but it passes through your digestive system as fiber, which helps keep you regular.
What it isn’t
Cellulose is not a sugar your body can use for energy, even though it's made of glucose units. The bonds linking those glucose molecules are arranged in a way human enzymes cannot break apart, so it passes through undigested.
Commonly misused online
People often call any plant fiber "cellulose" when they mean dietary fiber broadly. While cellulose is a type of fiber, not all dietary fiber is cellulose—hemicellulose, pectin, and lignin are distinct compounds with different properties.