Vegetables and vegetable preparation. Vegetables are plants or parts of plants that are used as foods. So broad a definition includes all fruits, nuts and cereals that, although of vegetable origin, are not commonly classed as vegetables. The term vegetable has through usage come to apply in a more narrow sense to those plants or parts of plants that are served either raw or cooked as part of the main course of a meal. Sweet corn and rice are two examples of cereals that , through usage ,are sometimes given the place of vegetables on the table. Various parts of plants are used as food and vary in their water, protein , carbohydrate, vitamin , and mineral content. The Leaf Vegetables The leaf vegetables are high in water and low in carbohydrates. They contain only small amounts of protein and little or no fat. Their chief nutritive contributions to the diet are in minerals and vitamins. Leaves, in general , are important sources of iron, vitamin A value, riboflavin, and ascorbic acid. The greener the leaf , the higher is its vitamin A value. Green leaves are also one of the better vegetable sources of calcium but most of the calcium in spinach, chard and beet greens is combined with oxalic acid in the plant and is not available for absorption from the digestive tract.