Do all vegetables offer nutritional value? I wondered, so I asked a few nutrition experts. The responses may surprise you. This is part of a continuing series to keep you informed about the benefits of the "not-so-famous" fruits and vegetables.

ICEBERG LETTUCE

Value: It's an excellent source of vitamin K with one-sixth of a medium head (about six large leaves) containing 25 percent of your daily requirement. Notably, a serving also contains 8 percent of your daily requirement for vitamin A and 6 percent for folate, says Nicholas D. Gillitt, a nutrition researcher at Dole Nutrition Institute in California. Although water accounts for more than 95 percent of its weight, iceberg lettuce also contains a moderate amount of fiber and supplies modest amounts of omega-3 fats, antioxidants, vitamins and minerals, says Dr. Christopher E. Ramsden, author of Nutrition by the Numbers (Applied Nutritional Biochemistry, 2007). And, of course, it's low in calories.

Nutrients: One cup contains roughly 40 milligrams of omega-3 fats. "The same cup provides 100 milligrams of potassium, 360 International Units of vitamin A and a respectable 20 micrograms of folic acid, slightly more than a cup of kale. Although it's not the richest source of many micronutrients, everything present is beneficial, and it contains no detrimental components," Ramsden says.

Health perks: It has a large amount of vitamin K, which plays a role in blood clotting. Gillitt says, "Unfortunately, 80 percent of men and 59 percent of women fail to get enough of this vital nutrient, so iceberg lettuce offers an attractive way to get well up on your daily amount." Additionally, vitamin K is required to make at least three proteins that are essential for bone formation. "Studies have also linked diets adequate in vitamin K with a reduced risk of hip fracture in the elderly. In fact, the Framingham Heart Study found seniors with a dietary intake of 250 micrograms of vitamin K per day had a 65 percent lower risk of hip fractures than those with an intake of 50 micrograms per day (adequate intake is 120 mcg for men, 90 mcg for women). Also, encouraging research suggests that vitamin K may play a role in inhibiting the growth of tumors and cancer cells. Several studies have linked levels of vitamin K intake with stabilization of liver cancer in particular," Gillitt adds.

What else? Well, Jo Ann S. Carson, a professor of nutrition at the University of Texas Southwestern Medical Center in Dallas, says: "Eating a wedge of lettuce before the rest of your meal can provide some bulk that will satisfy you and may help you reduce the number of calories you consume from the more calorie-dense part of your meal."

Nutrition stats: (1 cup): 10 calories, 0.10 g fat, 2.14 g carbs, 0.9 g fiber, 0.65 g protein.

Purchasing: Carson says to look for a hardy green color. Even though iceberg lettuce is a lighter green than other lettuces, you can still get phytochemicals. The greener the leaves, the more phytochemicals (which are helpful to fight disease) they contain. Also, select a lightweight head — you will get more leaves of lettuce in a head that is relatively light for its size; a heavier head is likely to have more weight provided by the core.

Storage: "After purchase, rinse the head and dry on paper towels. (Leaving water on the lettuce will make it brown and spoil more quickly.) Refrigerate in a plastic bag or lettuce keeper for use within one week," Carson says.

CELERY

Value: It has potassium, calcium and folic acid. Plus, celery adds texture and crunch to many foods and is better than chips for your healthy dips. Ramsden puts it this way: "Like iceberg lettuce, this low-energy food can help fill your craving for 'crunch' without loading up on calories and junk foods."

Nutrients: Although water accounts for more than 95 percent of its weight, celery is a good source of fiber and supplies modest amounts of antioxidants, vitamins and minerals. One cup provides 260 milligrams of potassium, 40 milligrams of calcium and 36 micrograms of folic acid. Like iceberg lettuce, everything present is beneficial, and it contains no detrimental components. Ramsden says each serving of celery can be considered a small cup of water with a side of fiber and a pinch of beneficial micronutrients.

Health perks: "Celery is loaded with phytonutrients such as quercetin (which promotes prostate and brain health), and a recent study from Case Western Reserve University found that another celery phytonutrient, apigenin, may slow prostate tumor growth," says Gillitt.

While no studies have specifically examined the metabolic and health impacts of celery, its addition to the diet is likely to be beneficial for the following reasons: "Its very low ratio of nonfiber carbohydrates (sugar equivalents) to fiber will stabilize blood-sugar levels and increase satiety. Its high water content can help keep you hydrated. As a perfect substitute for chips, celery provides the desired 'crunch' without all the salt, and it also contains omega-6 fats and nonfiber carbohydrates," says Ramsden. Diets rich in folic acid have been associated with decreased risk of cardiovascular disease because it works in conjunction with vitamin B6 to reduce homocysteine, an amino acid that, at high levels, is a risk factor for artery blockage. Higher dietary fiber intakes are associated with a significant reduction in coronary heart disease risk by lowering LDL "bad" cholesterol, and higher potassium intakes are associated with significantly lower blood pressure.

Nutrition stats: (one large stalk): 10 calories, 0 g fat, 51 mg sodium, 166 mg potassium, 1.9 g carbs, 1 g fiber, 0.44 g protein.

Purchasing: The stalks should be firm, crisp, light green and without bruising or discoloration.

Storage: "Your best bet is to remove the base and discard any stalks or leaves that are damaged. Rinse thoroughly and place in a storage container or bag and it should last about two weeks," says Molly Morgan of Creative Nutrition Solutions in Vestal, N.Y.

PARSLEY

Value: It's not just a garnish; believe it or not, parsley is a nutrition powerhouse.

Nutrients: (1/4 cup): 1,264 IU vitamin A (25 percent), 20 milligrams vitamin C (33.2 percent), 0.93 milligrams iron (5.17 percent), 246 micrograms vitamin K (310 percent).

Health perks: A mere quarter-cup contains 300 percent of the recommended daily allowance for vitamin K (see iceberg lettuce) while also providing an excellent source of vitamins A (eye health) and C (skin and immunity). However, it is most often used in small amounts as a condiment or flavoring, which means that its nutrition impact is reduced. Parsley also contains the phytochemical myristicin, which animal studies have shown to inhibit tumor formation, particularly in the lungs. And it is a top source of the antioxidant flavonoid apigenin, which is said to protect the prostate, says Gillitt.

Nutrition stats: (1/4-cup): 5 calories, 0.12 g fat, 8 mg sodium, 0.95 g carbs, 0.5 g fiber, 0.45 g protein.

Purchasing: For best taste, buy fresh rather than dried. Look for vibrant green leaves, and make sure it's not wilted.

Storage: Wash, blot dry, then refrigerate in a sealed bag.

Charles Stuart Platkin is a nutrition and public-health advocate, and author of "Breaking the FAT Pattern" (Plume, 2006). Sign up for the free Diet Detective newsletter at www.dietdetective.com.