Why Humans Cannot Digest Cellulose


cannot digest cellulose as the digestive system of humans do not have


the enzyme which digests the cellulose. This article gives information about cellulose and cellulose digestion in animals.

What is Cellulose:

Cellulose is a polymer of beta-glucose with molecular formula (C6H10O5)n .It is composed of long chains of polymeric polysaccharide carbohydrate. The structure shows a linear chain of several hundreds to over ten thousand beta links to D-glucose units. Cellulose is the main constituent of the cell in the most plants and it is used in the manufacture of plant based products such as paper, textiles and organic pharmaceuticals.

How Animals Digest Cellulose:

Herbivorous animals digest cellulose and hemicellulose in two steps. First is mechanical digestion and second is enzymatic digestion.

Mechanical Digestion

: The strong fibers of the cellulose are broken up mechanically by the strong mouth parts of animals called mandibles and gastric mills that they have in their stomachs. As humans lack this gastric mills there is no chance of mechanical digestion of the cellulose. For instance: cow have more that one stomach and it chews the food by ruminating thoroughly.

Enzymatic Digestion:

The next level of digestion is enzymatic digestion where the food is digested by enzymatic action. Animals have symbiotic bacteria in their intestinal tract. These bacteria possess cellulase and other enzymes that are required for the digestion. The process of digestion is not completely understood but the it is hypothesised that this bacteria is responsible for the digestion of cellulose on animals.

Cellulose for Humans:

Although cellulose is not digestible by humans, it is taken in form of plant foods. Foods such as leafy vegetables and fruits adds cellulose to give the ‘fiber’ to the diet. Nutritionists and dietitians identify cellulose to be the useful part of food that keeps the move through the digestive tract efficiently. It is also proved that fiber rich diet can lower the risk of colon cancer.

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