Humans are unable to digest cellulose because the appropriate enzymes to breakdown the beta acetal linkages are lacking.

What kind of polysaccharides Cannot be digested by humans?

Cellulose – is another long chain polysaccharide made from many glucose building blocks. We often talk about cellulose as dietary fibre or what we used to call "roughage" as the human body is unable to break it down during digestion.

What molecules Cannot be digested by humans?

Water, minerals, vitamins, and cholesterol are not broken down; they are used by the body in the form in which they are taken in, so they cannot be used for energy. Fiber, a type of carbohydrate, cannot be completely digested by the human body so energy is not released from fiber when it is digested.