You are what you eat, but more importantly your unborn baby is what you eat. A baby's diet before it is born prepares it for the rest of its life. Any discrepancies in a mother's nutrition during those nine months and even the year before can seriously affect a baby's health.

To begin with, while you might be eating for two, remember, number two weighs not much more than a couple of Big Macs. Rose Ann Angotti Hudson, R.D. at the Columbia Hospital for Women, says "a pregnant woman only needs 300 more calories than she needed before pregnancy to maintain her weight."

At the same time, pregnancy is not a time to diet. Drastic restrictions in food intake will directly affect your developing baby by cutting off sufficient nutrient supplies. Also, if you try to lose body fat, the fat is broken down into ketone bodies, which are passed to the fetus, where they can cause damage to its developing brain and body. For the complete pregnancy, Hudson suggests a 22- to 27-pound weight gain.

A daily diet should include, according to Hudson, 4 or more servings of fruits and vegetables, 4 or more servings of bread or cereal, 4 or more servings of milk products and 3 or more servings of meat (2 to 3 ounces), fish (3 ounces), poultry (3 ounces) or eggs (2 eggs).

Because of the increase in vitamin and mineral requirements it would be wise to consume nutrient-rich calories instead of empty ones. So there really isn't such a thing as a free ice cream cone or candy bar even when you are pregnant.

The protein requirement increases by two-thirds during pregnancy, from 45 grams to about 75 grams a day. At least 1,200 mgs of calcium a day is recommended. One cup of milk supplies nearly 300 milligrams of calcium, but if you hate drinking milk, add the calcium in liquid or powdered form to soups, baked goods, casseroles and cooked cereals. Avoid adding chocolate because that reduces your body's ability to absorb calcium. For those with milk intolerance, there are acidophilus milk and Lactaid tablets and liquid that when consumed with milk and other dairy products can neutralize any uncomfortable symptoms.

Iron supplements of 35 to 60 milligrams a day are suggested, as is a folic acid supplement. Organ meats, dried fruits, prune juice, iron-fortified cereals and dried beans are all good iron sources.

"We do not recommend a salt-restricted diet during pregnancy," says Hudson, "because of the great increase in blood volume."

At least 6 to 8 glasses of fluids, including milk should be consumed to help maintain the increased amount of body fluids and to prevent constipation.

* "Pregnant women," says Hudson, "should avoid caffeine, drugs, alcohol, and though we have no proof, we still suggest they avoid saccharin and NutraSweet." There are conclusive studies, however, showing that it is dangerous to your baby for you to consume more than two drinks on any one day during pregnancy, even if you only drink once in a while.

Below is an elegant recipe that will provide protein, vitamins A and C, niacin, riboflavin and calcium. With butter, flour, salt and pepper in your cupboard, it will be just a short waddle through the express lane.

EXPRESS LANE: tangerines, lemons, parsley, scallions, bay leaf, sole fillets SOLE WITH TANGERINE SAUCE (4 servings)

7 tablespoons butter

2 teaspoons finely shredded tangerine peel

1/2 cup tangerine juice

1 teaspoon lemon juice

1 tablespoon finely chopped parsley plus extra for garnish

1 tablespoon finely chopped scallion

1 bay leaf

1 tangerine, peeled, sectioned and seeds removed

3 tablespoons flour

1/2 teaspoon salt

1/8 teaspoon ground black pepper

1 pound sole fillets

Combine 5 tablespoons butter, tangerine peel and juice, lemon juice, 1 tablespoon parsley, scallion and bay leaf in a saucepan. Bring to boiling and simmer over low heat until slightly thickened, stirring occasionally. Remove from heat; remove bay leaf and mix in tangerine sections. Keep sauce hot.

Mix flour, salt, and pepper; coat fish fillets. Heat 2 tablespoons butter in a skillet. Add fillets and fry until both sides are browned and fish flakes easily when tested with a fork.

Arrange fish on a hot platter and pour the hot sauce over it. Garnish with parsley.

Adapted from "Encyclopedia of Nutrition and Cooking," by Staff of Culinary Arts Institute (Grosset & Dunlap, 1974)