65% - Oxygen together with hydrogen form water, which is the primary solvent found in the body and is used to regulate temperature and osmotic pressure. Oxygen is found in many key organic compounds.

23% - Carbon has four bonding sites for other atoms, which makes it the key atom for organic chemistry. Carbon chains are used to build carbohydrates, fats, nucleic acids, and proteins. Breaking bonds with carbon is an energy source.

10% - Hydrogen is found in water and in all organic molecules.