Vegetables are included in the first four of the seven basic food groups: 1) leafy, green, and yellow vegetables; 2) citrus fruits, tomatoes, and raw cabbage; 3) potatoes, other vegetables, and fruits; 4) meat, poultry, fish, eggs, nuts, and dried peas and beans; 5) milk and milk products; 6) bread, flour, and cereal grains; 7) butter and fortified margarine.; and Nutritionists recommend the daily consumption of four servings from the first three food groups, including one serving from each of the first two. Once considered to be luxuries because of their high water content and relatively low energy value, many vegetables today are increasingly recognized as sources of vitamins, minerals, and bulk. Additional knowledge of nutrition is expected to increase the per capita consumption of vegetables.
Aside from nutritive value, vegetables are esteemed foods for additional reasons. Because of color, shape, texture, consistency, flavor, and aroma, vegetables appeal to humans' senses of taste, smell, vision, and touch and add to their enjoyment of a varied diet. Flavor and aroma vary from the subtle to the overpowering, with some vegetables prized for their distinctive taste and others for the way in which they combine with or complement other foods.
Carbohydrates
In many temperate-zone diets the potato, sweet potato, and squash are important staples providing carbohydrates, and vegetables high in carbohydrates, such as the cassava, yam, taro, and dasheen, are basic food to millions in the tropics. The carbohydrate content of these vegetables is largely starch, and such crops are known as starchy vegetables.
Another carbohydrate—sugar—makes up from 1% to 15% of some vegetables and contributes greatly to the taste of many fresh vegetables, especially melons and sweet corn.
Protein
Most vegetables are relatively poor sources of proteins. Fresh peas and lima beans, which contain 6% to 8% protein, are exceptions. Dried beans and peas are a more concentrated source of protein than are the succulent vegetables. Vegetarian diets often depend heavily on legumes for protein.
Fats and Oils
Vegetable fats are fats of plant origin, in contrast to animal fats. Most vegetables are extremely low in fats and oils and for this reason are often included in low-fat diets.
Minerals
Although vegetables are relatively low in mineral content, they are consumed in large enough quantities to function as important sources of many minerals. Calcium is in relatively good supply in collards, mustard greens, kale, dandelion greens, and broccoli. It is also present in some other vegetables, such as spinach, chard, and rhubarb, but in these the calcium is not available to the human body. Most vegetables are relatively low in sodium, another important mineral. Beets, carrots, celery, chard, and kale contain more sodium than do other vegetables. Potassium is supplied in part from vegetables. Since the soil is the ultimate source of minerals and trace elements in natural foods, vegetables serve a unique role in that they come from geographically widespread areas and thus tend to minimize the dietary effect of localized soil deficiencies.
Vitamins
Many vegetables have high vitamin contents. All vegetables contain vitamin C in varying amounts. The best sources of this vitamin include tomato, cauliflower, cantaloupe, cabbage, Brussels sprouts, sweet potato, pepper, potato, turnip, and broccoli. Many factors during growth influence vitamin C content, and after harvest, vegetables vary in their ability to retain this vitamin. Since processing and final cooking cause losses, raw vegetables are generally higher in this vitamin than are cooked vegetables.
Yellow and green vegetables contain carotene, which can be converted into vitamin A in the body. Vegetables such as collards, turnip greens, kale, carrot, squash, sweet potato, and cantaloupe in the diet will supply the vitamin A requirement.
The vitamins of the B complex are supplied in part by vegetables. Although vegetables contain relatively low concentrations of thiamine (vitamin B1), they can make a worthwhile overall contribution of this vitamin to the diet. Dry beans and peas are highest in thiamine among the vegetables. Riboflavin (vitamin B2) is present in leafy green vegetables in significant amounts. Another member of the vitamin B complex, niacin, is supplied in significant amounts by asparagus, collards, sweet corn, mushrooms, green peas, and lima beans. Vegetables are one of the best sources of vitamin B6 and are quite high in pantothenic acid, another B vitamin. They are also among the best sources of folic acid. They are not, however, known to furnish any vitamin B12. A number of vegetables contain other members of the B complex.
Green vegetables are good sources of vitamin E, and the green leafy vegetables, tomatoes, and cauliflower are good sources of vitamin K.
