The body cannot use the food that we eat until it is broken down into small molecules during the process of digestion.
Digestion is a process that begins in the mouth where the saliva and chewing start the sequence. When the food mixture is swallowed and reaches the stomach, digestive juices act on it starting the chemical breakdown. The food mixture travels next to the small intestine where digestive juices from the pancreas further break down the carbohydrate, fat and protein.
The liver produces bile, which is stored in the gall bladder and released when we eat. Bile dissolves dietary fat making it easier for enzymes from the pancreas and the intestinal lining to digest and absorb it.
Different nutrients in the food we eat are digested and absorbed differently.
Carbohydrate digestionCarbohydrates (also called 'sugars') are the most abundant part of our diet. It is recommended that 55% to 60% of total daily calories should come from carbohydrates. Digestible carbohydrates are broken down into simpler molecules by enzymes in the mouth, pancreas and small intestine.
Starch that we eat is digested in two steps. First, salivary and pancreatic juices break large starch molecules into smaller ones. Next, these are broken down further into glucose. Glucose and other simpler sugars can be used by the body or stored for future use.
Different enzymes in the digestive juices help break down different carbohydrates and sugars. Sugar from milk requires a different enzyme than sugars from fruit. Most of these enzymes are present in the lining of the small intestine.
Protein digestionProtein digestion starts in the stomach where large molecules are broken into smaller parts. Complete digestion happens only in the small intestine where all proteins are broken into amino acids and short groups of amino acids.
Blood transports these amino acids from the small intestine to other parts of the body.
Fat digestionThe bile from the liver dissolves the fat in the intestine to help the digestive juices to break it into smaller molecules such as fatty acids and cholesterol. The bile combines with these and helps in transporting them to various parts of the body.