Leeks are closely related to onions, as the similarity in flavor shows, and are distant cousins of asparagus. All 3 are members of the lily family. Although the entire leek is edible, most people prefer to eat the white, fleshy base and tender inner leaves and to discard the bitter dark green leaf tops.
Low-calorie leeks provide an appreciable amount of minerals and fiber together with plenty of vitamin C. A half cup of chopped, boiled leeks, served plain, contains only 15 calories but 25mg of vitamin C, as well as 16mg of calcium and a small amount of niacin. Vegetables in the onion group may have a protective effect against stomach cancer, and like onions, leeks may help lower cholesterol. On a more negative note, they can cause bad breath and, in some people, gassiness.
Leeks are useful in a range of dishes where tjeir mild oniony flavor is desired. You can boil and sieve them with potatoes for a chilled vichyssoise soup; braise them in fat-free stock to serve hot; and brush them lightly with olive oil and grill for a mixed-vegetable barbecue. To make a reduced-fat quiche, steam chopped leeks and mix them with eggs and low-fat yogurt.