Chemical Reactions in Food Digestion

The food you eat provides your body with the nutrients it needs to function properly. Most foods contain a mix of those essential nutrients, and your body must break it down through a series of chemical reactions to get what it needs in the form best used by your cells.

Essential Nutrients

The nutrients your body is aiming to get out of the food you eat through digestion include carbohydrate, protein, fat, vitamins and minerals. Carbohydrates, protein and fat are considered macronutrients because you need them in large amounts. They provide energy, nutrients to grow and repair tissue, and the components of your cell membranes. Vitamins and minerals, referred to as micronutrients, help your body carry out various functions, from red blood cell production to bone building.


Carb Digestion

Chemical digestion of carbohydrates begins in the mouth. Your saliva contains an enzyme called amylase that helps break down the complex unit of carbohydrates into simpler carbohydrates.

Digestion of carbohydrates continues in the small intestines, where carbohydrases, which are enzymes that break down carbohydrates, continue to process the carbohydrates into smaller units called glucose, which are absorbed into your bloodstream.

Protein Digestion

Protein digestion starts in the stomach. The acid in the stomach, along with the enzyme protease, starts to denature, or unravel, the protein strands for digestion.


Like carbohydrates, chemical digestion of proteins continues in the small intestines, where the proteases continue to break down the protein into amino acids, which are then absorbed through the walls of your intestines into your bloodstream.

Fat Digestion

All fat digestion takes place in the small intestines. Fat molecules are first mixed with bile, which is a substance made by your liver. Bile dissolves the fat to make it more water soluble, so the fat enzymes, called lipases, have an easier time breaking up the molecule. The lipases break the fat molecule into two parts, glycerol and fatty acid, which is then absorbed like glucose and amino acids.


Vitamins and Minerals

Water-soluble vitamins, such as the B vitamins and vitamin C, do not undergo any type of chemical digestion and are absorbed directly into your bloodstream through your small intestines. Bile is needed to help move the fat-soluble vitamins -- A, D, E, and K -- away from fat molecules before they can be absorbed. Minerals, such as potassium, iron and calcium, are absorbed differently depending on the mineral. For example, potassium is absorbed directly into the bloodstream, while calcium requires a carrier to transport it into your bloodstream.