How does food become a waste product in the large intestine?

Answer 1

The undigested food, a large amount of water and dissolved salts go into the large intestine from small intestine. After then water and salts are absorbed into the blood, while undigested material is rejected as faeces.

Answer 2

Your small intestine absorb the amino acids, sugars, glycerol, fatty acids, vitamins and minerals from the food. The rest of the waste is pushed forward to large intestine. The contents are totally in liquid form at the terminal end of the small intestine. The large amount of fluid is absorbed back in the large intestine. The contents become more and more solid as the waste material proceeds down the path. So the large intestine acts as the storage organ for faeces. The faeces are eliminated periodically.