What is metabolism?

Metabolism is the process in a living organism by which food is converted into energy. 

Carbohydrate Metabolism

1. We eat carbohydrates.
2. These carbohydrates are converted into glucose (sugar).
3. Glucose is then absorbed into the blood
4. With the help of insulin (a hormone produced in the pancreas), it is converted into energy

1 gram of fat produces 4 kcal (17 KJ) of energy

Lipid Metabolism (Fat metabolism)

1. We eat fats (triglycerides)
2. By the process of lipolysis, triglycerides are broken down into fatty acids.
3. Fatty acids enter the blood
4. Fatty acids are then converted to energy

1 gram of fat produces 9 kcal (37 KJ) of energy

Amino Acid Metabolism (Protein metabolism)

1. We eat proteins 
2. The pepsin (an enzyme present in the stomach) converts proteins into polypeptides. 
3. These polypeptides are then further broken down into smaller peptides by proteases enzymes (produced in the pancreas). 
4.  In the intestine, the small peptides are broken down into amino acids that can be absorbed into the bloodstream. 
5.  These amino acids are then utilized as an energy source

1 gram of fat produces 4 kcal (17 KJ) of energy