The chemicals needed  by organisms for life activities are called nutrients.  We can define the term nutrient as any  substance capable of one or more of the following functions:

Certain foods are said to be protective, apart from their plastic and/or energetic value, in that they play a notably significant role in the normal process of metabolism.

They consist of: grains, legumes, fruit and vegetables, milk, cheese, eggs, all  meats and fish etc. which owe  their protective action to the content of vitamins, oligodynamic elements, amino acids and essential fatty acids.

Others are said to be stimulants as they have a stimulating effect on the central nervous system,  thereby having influence on the chemical processes of digestion  and the absorption of food; tea, coffee, chocolate, alcohol etc. 

Others still are known as condiments among which are included some real foods ( fats, oils, salt, sugar, honey etc. ), aromatic substances ( vinegar, parsley, basil, rosemary, laurel, oregano etc. ) and those classified as drugs (pepper, mustard, cinnamon, nutmeg, cloves, etc. ).

The human organism, therefore needs a daily sustenance of foods making up the basic nutrients of carbohydrates, proteins, fats which supply the body with calories for energy in addition to the need for water, minerals and vitamins which are non-providers of calories.

The complex of reactions regarding chemical and biochemical transformations undergone by nutrients such as sugars, fatty acids, glycerol, amino acids contained in simple or complex carbohydrates, fats or proteins is simplified by the process  of digestion.  The combined actions of anabolism and catabolism make up metabolism ( a synonym for transformation).

Basic food functions relative to their nutritional content