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.