Fiber is essentially cellulose, a polysaccharide and the most prevalent on earth, second is N-acetylglucosamine, chitin, found primarily in fungi and crustaceans among others. The recommended daily intake by our overlords in the government is around 30 grams. When we had a plant base diet with no processed foods, people consumed more than 50 grams per day--thanks to the legumes and whole grains they consumed.
My dinner tonight: bulgur with garlic, onions and chick peas, grilled chicken, and toasted sourdough bread, blackberries for desert. Total fiber is well over 40 grams. Consider how well your intestines are by your stools. Sad to say we have become a nation of wimps.