Cells use carbohydrates, lipids and proteins as sources of chemical energy. Cells break down each into small molecules, which eventually produce carbon dioxide and water. Carbohydrates and proteins share more in common with each other than they do with lipids.
Carbohydrates, made up of monosaccharies, double-monosaccharides and starches, fuel cells. Two types of carbohydrates, disaccharides and starches, are digested and broken down into individual sugars. Cells and tissues absorb these sugars, which then fuel physical activity, store these sugars or convert these sugars into fat.
Twenty different amino acids make up proteins, which support every process. When proteins are digested, they create pools of amino acids that cells use to create new proteins. Muscles and organs are made up of proteins, and proteins help cells communicate and serve as an energy source. Like carbohydrates, proteins are water-soluble. Bodies convert proteins to sugars, much like they do to carbohydrates, and store proteins as fat.
Bodies use lipids differently than carbohydrates and proteins, though still converting lipids and fats to sources of energy. Bodies store lipids in fatty tissue, which protects and cushions internal organs. Lipids also make up cell membranes and support hormone regulation.
All cells have a combination of carbohydrates, proteins and lipids. Despite their differences, each produces molecules of acetyl-CoA, which fuel cellular reproduction and provide the energy a body needs to function.