Food is any material taken from a living source to give nutrition to an organism for its normal growth and maintenance. It includes any material that nourishes the living things being fed, including both plants and animals, with the added nourishment of vitamins, salts, sugar, or other nutrients. Plants feed on food, which they secrete from stalks, leaves, roots and seeds. Animals feed on food taken from the environment, which may include animal manure, dead leaves and other animals or plants.

Some food forms are complex systems of interactions between food, bacteria, and enzymes. Examples of such food structures are starch, sugars, and amino acids. Complex carbohydrates are found in vegetables, pulses, nuts, legumes, and whole grains. Polysaccharides and polyols are substances produced by various food materials that include hydrogenated oils, starches, cereals, potatoes, rice, wheat, corn, vegetables, and fruits. Sources of polyols include garlic, onions, milk, eggs, and chocolate.

Animal products such as meat, fish, milk, eggs, poultry, and fowl are the richest sources of protein and fat. Meat is divided into red meat and white meat. Lean meats are less rich in calories and fat than fatty meats. Milk is one of the most important sources of calcium, vitamin D, phosphorus, and protein.