At the level of molecular structure, can the dietary fibres be regarded as polymers?
Dietary fibers are the indigestible portion of food derived from plants.
Most of these are indeed polymers of sugars (that is, a chain of repeated basic unit of carbohydrate), for example cellulose, alginate or pectin. They have glycosidic bonds that cannot be broken down by enzymes found in humans, and are thus indigestible.
But there are exceptions, for example raffinose, a trisaccharide found in beans & cabbage, is also categorised as a dietary fiber, as it is not breakable by human enzymes.