Explain the general principles of digestion and metabolism of:

• proteins
• carbohydrates
• lipids

The digestion of proteins begins chemically in the stomach, where gastric juices initiate the breakdown. Pepsin breaks down the long chain of proteins into smaller ones. Metabolism of proteins involves the processes responsible for the synthesis of amino acids and proteins and the catabolism of proteins.

Step-by-step explanation

Digestion of carbohydrates begins in the mouth by salivary amylase. It then goes to the duodenum, where it is digested by pancreatic amylase. The body's energy is obtained from carbohydrates specifically glucose, which is broken down through glycolysis to generate Adenosine Triphosphate (ATP).

Digestion of lipids begins in the mouth by the lingual lipase and in the stomach by gastric lipase. The free fatty acids are absorbed in the body and metabolized to provide body organs with energy during prolonged starvation