Digestion of the polysaccharides of some cereal foods in the human small intestine.

The digestion and absorption of dietary starch and nonstarch polysaccharides (NSP) in the small intestine of man from oats, cornflakes, and white bread has been determined by feeding seven ileostomists test meals containing these foods and estimating carbohydrate recovery in the effluent. NSP, the main constituent of dietary fiber, was almost completely recovered from all three test meals, including the water soluble beta-glucan which is the main NSP in oats. Less than 0.6% of the starch in oats was recovered as starch with a further 1.2% as dextrins and maltose. 4% of cornflake starch however was recovered, of which the main part was resistant to alpha-amylase digestion in vitro unless specially dispersed. Similarly with white bread 2.5% of ingested starch reached the terminal ileum of which the greater part was starch resistant to alpha-amylase in vitro. Overall 5.8% of the carbohydrate in white bread, 5.3% in cornflakes, and 11.7% in oats was recovered. This study supports the view that human digestive enzymes do not break down dietary NSP. It also identifies a fraction of starch, RS, present in processed food which resists breakdown by alpha-amylase both in vitro and in the small intestine of man.