The process by which absorbed simple food participates in the formation of the body or protoplasm in the organism is called assimilation.
1. Carbohydrate assimilation: Carbohydrates are digested into glucose, fructose and galactose. Glucose, fructose and galactose are absorbed by body cells. Absorbed glucose is burned in the body’s cells to produce energy. Excess glucose is stored as glycogen. Small amounts of monosaccharides are converted to proteins and lipids.
2. Protein assimilation: Protein is digested and converted into amino acids. Amino acids are absorbed by body cells. Absorbed amino acids form protoplasm, cytoplasm, enzymes, hormones etc. Some amino acids are oxidized to produce energy. Small amounts of amino acids are converted to sugars.
3. Lipid assimilation: Lipids are digested and converted into fatty acids and glycerol. Fatty acids and glycerol are absorbed by body cells. Absorbed fatty acids and glycerol form phospholipids, lipoproteins, cholesterol etc. in body cells. Some are stored as fat under the skin as food. A small amount is synthesized as carbohydrates and proteins.