carbohydrate digestion

Last reviewed 01/2018

Carbohydrate digestion is necessary because the gastrointestinal tract can only absorb monosaccharides.

It is dependent on several types of enzyme:

  • alpha-amylases:
    • hydrolyze alpha-1,4 bonds to convert polysaccharides with alpha-1,4 bonds e.g. glycogen and starch, into oligo- and disaccharides such as maltose and alpha-limit dextrins
    • the first amylase that food encounters is oral ptyalin which works until inactivated by stomach acidity
    • pancreatic amylase carries out the same reaction from the duodenum distally

  • disaccharidases:
    • found in association with the small intestinal brush border
    • sucrase: hydrolyzes sucrose to glucose and fructose
    • maltase: hydrolyzes maltose to 2 glucose residues or maltose triose to 3 glucose residues
    • lactase: converts lactose into glucose and galactose
    • alpha-limit dextrinase: hydrolyzes dextrins into short chains of glucose residues

  • 1,6-glucosidase:
    • secreted by the small intestine
    • hydrolyzes branched dextrins

Therefore ultimately, dietary carbohydrate is digested into glucose, fructose and galactose.