Food is any material eaten to supply nutrition to an organism. In its simplest terms food is any material made up of living material that can be used to provide nourishment. Food is typically of animal, plant or fungus origin, and includes various nutrients, including proteins, vitamins, carbohydrates, fats, or minerals. Plants include all plants that produce food, such as grain, oil, hay, fruits, vegetables and sometimes grass. Fungi include fungi that consume matter as a source of food.

Animal species include all mammals that have an anatomy capable of digesting both protein and fat. The remainder of animal anatomy is composed of tendons, muscles, bones, organs, blood, tendons, ligaments, and hairs. Vegetarians, unlike omnivores, are not necessarily devoid of meat, as many vegetarians eat fish, poultry, eggs, milk, cheese and other dairy products.

The majority of carbohydrates in food are found in starches such as glucose, sucrose, fructose and galactose, although other complex carbohydrates may also be consumed. Fats are either fatty acids or alkaloids found in plants. Some fats are naturally produced by the body and essential for human health, but excessive consumption may lead to obesity. Amino acids are those molecules that make up the basic building blocks of life. These include amino acids produced by the liver, muscles, blood and other tissues and essential fatty acids found in fish, dairy products, nuts, seeds and lean meats.