Food is any material eaten to provide nutrition to an organism for its specific needs. The human body is the only organ that does not require food, although other organisms, such as bacteria and yeast, do require nutrition for their survival. Food is generally of animal, plant or fungi origin, and includes essential nutrients, including proteins, carbohydrates, vitamins, or other minerals.

Plants contain carbohydrates, while animal proteins are found in proteins and fats. Fungi contain carbohydrates and may also contain vitamin B-12, but not until they have been adequately fed for a period of time, at which time they can become available for absorption in the human diet. All three kinds of food are needed by all the organs of the body, but some are more beneficial to the body than others.

Carbohydrates provide the bulk of the calories that we consume. Therefore, whole grains, rice, potatoes, cereals, pasta and bread are ideal dietary sources of carbohydrates. There are many different kinds of carbohydrates, including glucose (sugar), lactose, fruit sugar, cellulose and non-cellulose sugars. Fruits and vegetables are naturally fibrous foods, but some of the fruits, vegetables and some legumes (such as beans) are not. Vegetarians usually need to eat more fibrous food than meat-eaters because they cannot eat meat or milk products.