Physiology of Nutrient Utilization

Physiology of Nutrient Utilization
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Physiology of Nutrient Utilization
Fig 1 Digestion and absorption of carbohydrates (LibreTexts, 2020)
Carbohydrates
Macronutrient source
Some of the major sources of carbohydrates include vegetables, whole grains, fruits, milk, and other dairy products. Certain vegetables and grains such as corn and potatoes also contain starch although sweet potatoes have sucrose but not starch. Dark-green green vegetables and fruits contain little to no starch although they can be a good source of sugars as well as dietary fiber. Slavin and Carlson (2014) recommend that people should select foods that are rich in dietary fiber such as cereals, whole-grain, bread, legumes, fruits, and vegetables. Usually, fruits and vegetables are not the recommended food sources with fiber but they have important micronutrients. in addition, milk and other dairy products have lactose but not fiber although they are necessary for the body as they provide vitamin D, calcium, and proteins.
Digestion
Digestion of carbohydrates begins in the mouth. In the mouth, the salivary glands secrete saliva that contains an enzyme known as salivary amylase. The enzyme works by breaking the bonds that hold the monomeric sugar units of oligosaccharides, disaccharides, and starch. Salivary amylase derives its name from the substrates it works upon known as amylose and amylopectin which are broken down into maltose and dextrin (LibreTexts, 2020). The entry of chyme into the small intestines signals the pancreas to release pancreatic juice through its ducts. Enzymes in the pancreatic juice together with other enzymes released by the intestinal cell linings help break down disaccharides into simple sugars known as glucose and galactose. These enzymes are collectively known as maltase, sucrase, and lactase. Digestion of starch ends in the small intestines where pancreatic amylase secreted by the pancreas hydrolyses the glycosidic bonds that hold the polysaccharide to form simple sugars. In particular, ...