Human Nutrition 3(3+0)

Lesson 10 : Digestion and Absorption of Carbohydrates and Fats

Digestion and absorption of carbohydrates

• The carbohydrates of the diet consist predominantly of starch together with varying amounts of sucrose (sugar), lactose (milk), glycogen (meat or liver) and fructose (fruits).
• The diets also contain varying amounts of indigestible carbohydrates such as cellulose, hemicelluloses, pentosans, etc.

The digestion and absorption of carbohydrates are briefly described below:

• Mouth: Very little digestion takes place in the mouth. The digestion of starch by salivary amylase continues in the stomach for 10-15 minutes, till the food gets mixed with gastric juice and the action of amylase ceases due to high acidity.
• Stomach: Hydrolysis (inversion) of some of the sucrose present in the food may take place in the stomach by the action of HCL.
• Small Intestines: A greater part of the starch and glycogen present in the food is digested by the pancreatic amylase in the small intestines into a mixture of maltose and isomaltose.

The resulting disaccharides-maltose (mainly) and isomaltose-along with sucrose and lactose present in the diet are digested by the different disaccharases present in the intestinal mucosa into the corresponding monosaccharides as indicated below.

The resulting monosaccharides, viz., glucose (most abundant) fructose and galactose are absorbed in the small intestine. Some quantity of pentoses presents in the diet or liberated from the digestion of nucleic acid are also absorbed.

Absorption of Monosaccharides