This article is about food for all organisms. For foods that starts with l for humans, see Human food. Food is any substance consumed by an organism for nutritional support.

Omnivorous humans are highly adaptable and have adapted to obtain food in many different ecosystems. Food is any substance consumed to provide nutritional support and energy to an organism. It can be raw, processed or formulated and is consumed orally by animals for growth, health or pleasure. Human food can be classified in various ways, either by related content or by how the food is processed.

The number and composition of food groups can vary. Most systems include four basic groups that describe their origin and relative nutritional function: Vegetables and Fruit, Cereals and Bread, Dairy, and Meat. In a given ecosystem, food forms a web of interlocking chains with primary producers at the bottom and apex predators at the top. Humans are omnivores finding sustenance in vegetables, fruits, cooked meat, milk, eggs, mushrooms and seaweed. Cereal grain is a staple food that provides more food energy worldwide than any other type of crop. Photosynthesis is the ultimate source of energy and food for nearly all life on earth.

It is the main food source for plants, algae and certain bacteria. Without this all organisms which depend on these organisms further up the food chain would be unable to exist, from coral to lions. Plants also absorb important nutrients and minerals from the air, water and soil. Carbon, oxygen and hydrogen are absorbed from the air or water and are the basic nutrients needed for plant survival. Plants as a food source are often divided into seeds, fruits, vegetables, legumes, grains and nuts. Where plants fall within these categories can vary with botanically described fruits such as the tomato, squash, pepper and eggplant or seeds like peas commonly considered vegetables. Plants have high carbohydrate, protein and lipid content, with carbohydrates mainly in the form of starch, fructose, glucose and other sugars.