Food is any material consumed to supply nutrition to an organisms. In the simplest sense food is any material that is consumed to sustain life; in the widest sense food is anything consumed to maintain health. Food is generally of plant, animal, or fungi origin, and has necessary nutrients, including protein, vitamins, carbohydrates, fat, and minerals. There are five basic categories of food, which are plant foods, meats, dairy, fruits, and vegetable foods.

Plant food includes all plant foods (all organic foods); animal products include meat, milk, eggs, fish, and poultry. Fishes include sea fish, herring, tuna, halibut, salmon, sturgeon, and scallops. Milk is either derived from cow, goat, or other animal sources; fruits are either from fruits or from vegetables. Vegetable foods include beans, green beans, potatoes, squash, carrots, corn, leafy vegetables, potatoes, spinach, cabbage, tomatoes, cucumber, and eggplant. The human diet contains about 70% of its total calories; carbohydrates make up another percentage and fats a smaller percentage.

Diets of good quality consist mainly of vegetables, fruits, and grains with minor amounts of meat, dairy, and eggs. The best dietary sources of nutrition are whole grains (especially bran), seeds, nuts, legumes (beans, lentils, peas), and whole soybeans. To be truly healthy one must eat a varied and complete diet that is nutritionally adequate. Many foods that are classified as unhealthy can actually be nutritious foods if they are eaten in moderation and in conjunction with other good dietary habits.