Nutrients

By definition, a nutrient is any element or compound that is necessary for or contributes to an organism's metabolism, growth, or other functioning. Essential nutrients must be supplied from an outside source because they cannot be synthesized by the body in sufficient amounts.

Commonly they are divided into 6 main categories:

Water (H2O), essential for life and required for the body's digestive and transportation system, as a lubricant, and for many other functions
Proteins, nitrogenous organic compounds that provide the building blocks (amino acids) for enzymes, other protein formations within the body and various other substances that control and regulate the metabolism
Fats, compounds of three fatty acids linked to a central glycerine molecule
Carbohydrates, sugar-based compounds that mostly contribute energy
Vitamins, various compounds essential to the body's functioning
Minerals, trace elements, pure elements, salts, or ions such as copper and iron

There are others, such as for example probiotics, enzymes and phytonutrients, which also play important roles but are still often overlooked in human nutrition and even moreso in pet foods. This section will give an overview of each group.