Some types of lettuce and other salad greens conain high amounts of beta carotene, folate, vitamin C, calcium, iron and potassium, but the amounts vay considerably from one variety to another. In general, those with dark green or other deeply colored leaves have more eta corotene and vitamin C than other paler varieties. Romaine and Boston lettuce, for example, have 3 times more vitamin C and much more beta corotene than iceberg lettuce.
Such salad greens as arugula, chicory, escarole, mache, and watercress are all more nutritious than lettuce; many people also find them more flavorful, and they are readily available in restaurants and markets. Some, such as chicory, escarole and watercress, are slightlu bitter, yet they provide an interesting flavor and texture contrast when added to a salad of lettuce and other types of greens.
Arugula, a member of the same plant family as broccoli, cabbage and other cruciferous vegetables, has a tangy, peppery flavor when grown during the cool spring and fall months, and a stronger, mustardlike taste if harvested during the summer. This is one of the most nutritious of all salad greens; 1 cup provides 2mg of beta carotene, 45mg of vitamin C, 150mg of calcium, and 0.5mg of iron—all in a serving that has only 12 calories! watercress, another cruciferous vegetable, is also a nutritional winner: 1 cup contains a mere 5 calories; yet it provides 1.5 mg of beta carotene, 15mg of vitamin C, 60mg of calcium, and 0.5mg of iron. Deeply colored lettuces and grees are also high in flavonoids, plant pigments known to work with vitamin C and other antioxidants to prevent cancer-causing cell damage.
Lettuce and other greens can be mixed or combined with a broad spectrum of raw fruits and vegetables, cold pasta, or chunks of chicken or tuna to make a low-calorie, highly nutritious main dish. Raw spinach is often used as a salad green; although cooking makes some of its nutrients a bit easier to absorb, a spinach salad still provides a good amount of beta carotene, vitamin C, calcium, and iron.