Does eating an extra 500 calories a day without gaining weight sound like a dream? For most people, it is. But for a special group — mothers who breast-feed their babies — it is a dream that can come true. But don't start dreaming about 500 calories worth of just anything. While a Breast-feeding diet allows for extra calories, those calories should come from nutritious foods. Both the mother's and the baby \'s health depend on the mother s choice of food.

Breast-feeding mothers can eat those extra calories because milk production requires so much energy. In fact, sometimes the energy demands of milk production are so high that even those 500 extra calories are not enough. Fortunately, most mothers can still meet these energy demands from fat stored during pregnancy.

While they are pregnant, women who eat a healthy diet and stay within the number of calories recommended by their doctors usually gain about eight to 10 pounds of fat. This may add about a third more body fat than the mother had before she became pregnant. The body sets in this supply of fat as insurance that calories will be available to produce enough milk after the baby is born.

Exactly how many calories should a Breast-feeding mother eat? The National Academy of Sciences recommends that a woman who is 5 feet 4 inches tall and weighs about 120 pounds eat 2,600 calories a day while nursing. This is in comparison to a recommended 2,400 calories a day while pregnant and 2,100 calories a day when neither pregnant or nursing.

Yet a mother can have a poor diet — either nutritionally inadequate or too low in calories, or both — and still produce enough milk for her baby. This is especially true during the first few months of Breast-feeding when the extra fat from pregnancy is available. But as those fat reserves are depleted, the amount of milk produced may decrease.

With a poor diet, any milk production will take its toll on the mother. Lack of protein may cause the breakdown of lean body tissue (muscle); not enough calcium could cause a loss of that important mineral from her bones. And because an inadequate diet can cause a decreased sense of well-being, there is a greater chance that a mother will give up Breast-feeding. As Julie Stock of the La Leche League, an international Breast-feeding support and educational organization, explains, a mother who is not t eating properly "simply is not in any shape to accept the stress of a tiny, nursing baby."

A mother should do everything she can to keep Breast-feeding her baby. Human milk is the ideal nourishment for human babies. Its protein content is particularly suited to a baby s metabolism, and the fat content is more easily absorbed and digested than the fats in cow s milk. Breast milk — because it contains antibodies from the mother — also can provide immunologic protection against certain diseases, infections and allergies. Formula can t do this.

A healthy breast-feeding diet is basically the same nutritionally sound and varied diet recommended during pregnancy. The main differences are in the needs for extra calories, fluids and certain vitamins.

Ten to 12 eight-ounce glasses of fluid per day preferably milk, fruit juices, or water — are necessary to make enough milk and prevent dehydration in the mother. Drinking something every time the baby nurses, in addition to drinking with meals, is one way to be sure to get enough.

Getting enough calcium requires special attention. Breast milk contains approximately 300 milligrams of calcium per liter. Since daily milk production averages 850 milliliters, approximately 250 milligrams of calcium are needed each day just for the breast milk. To ensure that the calcium for the breast milk is not t drawn from the mother s bones, which could contribute to osteoporosis (weakened bones) later in life, the National Academy of Sciences recommends 1,400 milligrams of calcium a day for Breast-feeding women.

A breast-feeding mother's need for iron is about the same as before she got pregnant. Iron loss from lactation is one-half to one milligram per day. Over a month, that amount adds up to approximately the same amount lost during a menstrual period. And menstruation frequently does not t resume until after Breast-feeding stops. However, many physicians recommend that a Breast-feeding mother take an iron supplement to replenish iron lost during pregnancy.

Although extra amounts of vitamins, such as A and C, are needed while Breast-feeding, a well-balanced diet should make supplements unnecessary. What makes up a well-balanced diet? The American Academy of Pediatrics recommends the following for breast-feeding mothers.

• Dairy Products — These contain not only calcium, but also protein, fats, vitamins and other minerals. The diet of a breast-feeding woman should include five servings of milk or milk products every day. While milk is an excellent way to meet the requirements for liquids and calcium, there are plenty of other sources of calcium. One cup of yogurt, two cups of cottage cheese, or one-and-a-half ounces of cheese contain about the same amount of calcium as an eight-ounce glass of milk.

• Protein Foods — Necessary for building muscle and other body tissue in both mother and baby, protein is found in animal products such as meat, fish, poultry, milk and eggs. Some vegetables also are good sources of protein. Four servings of protein should be part of the nursing mother s daily diet. For lean cooked meat, fish or poultry, without bones, two to three ounces is the usual serving size. Good sources of vegetable protein include dried beans such as kidney and lima (one cup), dried peas (one cup), and peanut butter (four tablespoons).

• Fruits and Vegetables — Fruits and vegetables provideimportant vitamins, minerals and fiber. Breast-feeding mothers should have several servings daily of fruits and vegetables, at least one from each of three subgroups:

• Foods rich in vitamin C include cantaloupe (serving size: half of a medium-sized melon) and strawberries (three-quarters of a cup) and, of course, citrus fruits such as oranges (one medium) and grapefruit (one half). Tomatoes, potatoes, and green peppers are also good sources of vitamin C.

• The dark-green vegetables subgroup includes greens, asparagus and spinach. These vegetables are excellent sources of vitamin A, which is important to babies for bone growth, tooth formation, good vision, and resisting infections.

• Dark-yellow fruits and vegetables are another good source of vitamin A. Examples of these are carrots (one-half cup per serving), sweet potatoes (one medium-sized), winter squash (one-half cup), and apricots (two medium-sized).

• Breads and Cereals — Carbohydrates from breads and cereals are a quick and efficient source of energy. Grain products also supply essential vitamins and minerals for the development of a baby s muscles, nerves and brain cells. Products made from whole grains provide more fiber than refined grains. Good choices for one of the four servings of these foods needed every day include whole-wheat bread (one slice), oatmeal (one-half cup cooked), spaghetti (one-half cup cooked) and brown rice (one-half cup cooked).

Knowing what to eat is only part of the battle. The demands of a baby may leave a mother with very little time or energy for cooking. But there are plenty of healthy foods that are quick and convenient. Fruits such as apples and bananas are good choices. Other quick and nutritious foods include ready-to-eat cereal, a glass of milk, cheese, rice cakes, yogurt, and fresh vegetables.

Nursing mothers usually can eat most foods. (Some drugs and certain other substances must be avoided or used with caution.) If a nursing mother has to give up a certain food or group of foods (if she or her baby has an allergy, for example), she should be sure to eat other foods that have a similar nutrient content.

Physicians rarely recommend weight-loss diets to Breast-feeding mothers. Instead, until breast-feeding stops, the best thing to do is sit back and enjoy those extra calories.