The Healthy Diet »

Virtually all vegetables are nutritionally dense. For example, one and a half cups of Romaine lettuce can supply half your daily requirement of vitamin A in the form of beta carotene (which the body converts to vitamin A), a third of your vitamin C and almost 10 percent of your iron — all in only 12 calories. Three and a half ounces of collard greens — 40 calories — provide more vitamin A and C than you need daily, more than 20 percent of your daily requirements of potassium, calcium and riboflavin (a B vitamin necessary for energy production in cells), and about 10 per­cent of your thiamin and niacin requirements. Even half a cup of the starchiest vegetables, such as potatoes, squash and corn, contains fewer calories than a tablespoon of butter. Furthermore, most vegeta­bles are low in sodium and fat and high in fiber, the indigestible portion of a plant.

Vegetables keep you healthy in several ways. A recent study at Johns Hopkins University showed that a high blood level of betacarotene, which virtually all leafy green and yellow vegetables contain, appears to reduce the risk of some kinds of cancer by protecting cells and tissues from harmful chemicals called free radicals. A diet with one or more daily servings of cruciferous vegetables, which include broccoli, Brussels sprouts and cauliflower, helps protect against cancer. Studies also show that certain vegetable fibers — lignins, pec­tins and gums — appear to lower serum cholesterol, may reduce the risk of arteriosclerosis, promote regularity and may guard against certain forms of cancer.

A vegetable's nutrient content depends largely on the part of the plant it comes from. The leafy parts of plants generally contain a great deal of water and very few carbohydrates; yet they supply substantial amounts of beta carotene, vitamin C and riboflavin. Dark green leaves, such as those of spinach and mustard greens, contain more beta carotene than do pale leaves, like those of iceberg lettuce. A dark-green color usually signals high calcium content, but because some dark-green vegetables contain oxalic acid — a calcium inhibi­tor — you should not rely on them as your primary calcium source.

Fruit vegetables, such as tomatoes, cucumbers and bell peppers, are the pulpy, seed-bearing part of the plant. They are slightly higher in calories than leafy vegetables and contain large quantities of vitamin C. Because their peels contain fiber and protect the vitamins under the surface, it is best not to peel these vegetables — or any vegetables with skins — before you eat them. If a recipe calls for peeling, peel vegetables as thinly as possible and just before you cook them.

Vegetables from the buds, stalks and flowers of plants, such as asparagus, broccoli and cauliflower, are low in calories and high in vitamins and minerals. Broccoli, for example, is particularly high -vitamin C and calcium; its leaves have four times the calcium and twice the beta carotene and riboflavin of its florets.

Root, bulb and tuber vegetables, such as potatoes, beets and carrots, have less water, more carbohydrates and more calories per serving than most other vegetables. Potatoes, both white and sweet, contain substantial amounts of vitamin C. The skins are high in fiber. And sweet potatoes and carrots also have exceptionally high amounts of beta carotene. (The average sweet potato supplies about five times the required daily amount of vitamin A.) The darker its yellow color, the more beta carotene a vegetable contains.

Before you cook fresh vegetables, wash them under a steady stream of water to get rid of dirt, insects, surface pesticides arA bacteria. Sandy greens, such as spinach and arugula, should be soaked briefly in the sink, using sev~ral changes of water (long soaking may remove nutrients). Do not cut fresh vegetables until you are ready t4cook them: Exposure to air destroys their vitamin C and A, whil light lowers their riboflavin and vitamin K content.

Steaming vegetables until they are just crisp-tender makes them taste better and preserves more vitamins and minerals than boiling. Use a vegetable steamer or other container with a tight-fitting lid. If Possible keep the vegetables from touching the boiling water and them loosely enough for the steam to circulate well.

If you boil vegetables, use as little water as possible, since water, - nutrients. To retain the most vitamin C, bring the water to a before you put in the vegetables. Remove vegetables from the while they are still firm; otherwise, they may become soft from overcooking. The cooking water, which contains vitamins and minerals can be used as the base for soups or sauces.

You can also stir-fry vegetables in a wok or heavy skillet, using one two tablespoons of vegetable or olive oil. The vegetables should be uniformly so that they all cook at about the same rate. Before the vegetables, heat the oil so that it is very hot but not smoking. Add soft, thin vegetables like spinach or chard at the last moment — they will cook in less than a minute.

When cooking frozen vegetables, do not automatically follow the directions. For firmer, better-tasting vegetables, try reducing suggested cooking time. Serve cooked vegetables immediately: The longer they sit, the more their vitamin content decreases.

The recipes that follow offer an interesting and satisfying variety of ways to cook and serve vegetables. Many of them provide hearty, main courses without using meat — allowing you to put nutritional punch into a meal with relatively few calories.

Buying and Storing Guide

1. In general, yellow and green vegetables that are dark, young and small have the best taste and the most nutrients. Fresh vegetablesem11y the best nutritional buy and frozen are second best. Canned vegetables — which consistency and nutrients during high-heat, processing — should be your, last choice. For the best, quality and value, buy vegetables in season and shop at roadside farm stands whenever possible.

2. When shopping in supermarkets buy unwrapped produce that you can inspect and select individually. Prewrapped items may be damaged or of inconsistent quality. Check to see that no part of vegetable is damaged or wilted. Aging and bruising release enzymes that lower the vitamin content.

3. Buy no more than you will eat in a few days : as soon as vegetables have been picked their natural sugar begins to change to starch and they begin to lose their sweetness. Most vegetables shold be stored in the refrigerator until you are ready to eat them. After buying root vegetables, such as beets or carrots, remove their tops right away: otherwise, their leaves will let moisture escape. Tomatores should be allowed to ripen at room temperature before they are refrigerated. White potatoes, sweet potatoes and onions should be kept ina well ventilated place that is cool, dark and dry.

4. You can freeze many fresh vegetables and preserve most of their nutrients. But if you freeze vegetables after cooking them, they will be soft, less tasty and less nutritious when you reheat them. Cooked vegetables can be kept refrigerated for about five days: Store them in plastic bags or tightly covered containers.