When the eggplant -- a native of Asia and Northern Africa -- was first introduced in Europe in the Middle Ages, botanists believed that consuming it would cause insanity. Its membership in the nightshade family of plants was the cause.

Nightshades, among them potatoes, tomatoes and peppers, also include poisonous plants such as jimson weed and bittersweet -- a viny plant with tiny, bright-red berries. Scientists advise people to avoid the leaves of the eggplant, which contain compounds that may be harmful.

The eggplant should not be condemned for having disreputable relatives, although some people consider taste reason enough. Eggplants have a slightly bitter, astringent flavor and spongy texture.

Known scientifically as a fruit, the eggplant comes in a rainbow of colors and varieties ranging from the skinny, Chinese white to the tiny, Asian bitter orange and the Italian purple and white Rosa Bianco. They vary in size from a few inches to more than a foot long and in shape from round to oblong, said Barry Swanson, a professor of food science at Washington State University in Pullman.

There are subtle differences in flavor. Large, white eggplants are firmer in texture and milder in flavor, while the small, round Thai versions are more bitter. Smaller eggplants, like the Thai green, are used in stronger flavored foods such as curries and pickled dishes.

Most grocery stores will carry the familiar, globe-shaped, deep purple commercial variety. Exotic types can be found in Oriental and specialty food stores.

The eggplant has moderate amounts of a wide range of nutrients. It is very low in sodium and fat and has no cholesterol. One cup of cooked, steamed eggplant has 25 calories, trace amounts of fat, 1 milligram of sodium and 238 mg. of potassium. Ninety-two percent is water.

"It is better to eat foods {like eggplant} that provide a variety of nutrients rather than planning your diet based on certain ones," said Karen Miller-Kovach, assistant director of nutrition for the Cleveland Clinic Foundation.

Eggplant is often used as a meat substitute, not because it is high in protein -- a cup has 1 mg. -- but because of its spongy texture. It easily absorbs the flavors of other foods and can be used in place of meat in lasagna, for example. Vegetarian Moussaka, a Greek dish, is another alternative.

Most recipes suggest salting the eggplant first before cooking to remove some of the bitterness. The salt can later be rinsed off.

Diet-conscious chefs bake or broil an eggplant because when frying or saute'ing, "it literally drinks oil," said Kovach. One tablespoon of olive oil, for example, has 14 grams of fat and 125 calories.

To select an eggplant, Swanson recommends checking for black spots, which indicate it has been stored at too cold a temperature. The skin should be tight and firm. Inspect the blossum end -- opposite the stem -- for signs of mold. If the area is soft, it means the mold has penetrated.

Eggplants should be stored at 40 to 50 degrees Fahrenheit and cooked within one to two days of purchase.