Tomatoes are one of the most frequently consumed "vegetables" in the United States, whether raw, steamed, fried, stewed, crushed, pureed, or reduced to a sauce. Though thought of as a vegetable, tomatoes are botanically classified as fruits. They are also one of our best sources of vitamin C.

Health Benefits
While not bursting at the seams with vitamins and minerals, tomatoes are indeed rich in vitamin C. This antioxidant plays a key role in maintaining a healthy immune system. They also contain beta-carotene and several other carotenoids that may have their own disease-preventing properties, particularly against heart disease and cancer. One carotenoid, lycopene, may help reduce the risk of prostate cancer. Tomatoes also offer a good dose of that possible stroke preventer, potassium.

Selection and Storage
Red or yellow, tomatoes fall into several groups: cherry, grape, plum, and round slicing tomatoes. Cherry and grape tomatoes are bite-sized. Italian plum tomatoes are oval. Slicing tomatoes are large and round, perfect for sandwich slices. Beefsteaks are a popular variety of slicing tomatoes.
Though available year-round, you may not want to eat what passes for fresh tomatoes in the wintertime. The best-tasting tomatoes are "vine-ripened," that is, they've been allowed to ripen on the vine, so they aren't made to ripen artificially. You may have to shop farmers' markets to find them. Moreover, there is no standard definition for the term "vine-ripened." Know your vendor before you trust the claim.
Look for tomatoes that are firm and well-shaped and have a noticeable fragrance. They should be heavy for their size and yield to slight pressure when gently squeezed, but they should not be overly soft. A common mistake is to store tomatoes in the refrigerator. Cold temperatures ruin the taste and texture of a good tomato. Also, wait until you're just ready to serve them before you slice them; once cut, flavor fades.

Preparation and Serving Tips
Salads seem more complete with a ripe, red tomato. Sliced tomatoes, served on a bed of radicchio or arugula, drizzled with a flavored vinaigrette or balsamic vinegar, and topped with fresh basil can't be beat. Chopped fresh tomatoes add flavor, color, and nutrition to soups, stews, and casseroles. They're superb on hot pasta.
With a tomato, you get loads of flavor with very few calories. Continue your weight-loss routine of healthy eating with this versatile, delicious fruit.

Nutritional Values Tomatoes, Fresh
Serving Size: 1 medium tomato           Calories: 24
Fat: 0 g
Saturated Fat: 0 g
Cholesterol: 0 mg
Carbohydrate: 5 g
Protein: 1 g
Dietary Fiber: 1 g
Sodium: 6 mg
Vitamin A: 1,025 IU
Vitamin C: 15 mg
Potassium: 292 mg
Carotenoids: 3,992 mcg

Source:
Gayle Povis Alleman, M.S., R.D., Densie Webb, Ph.D., R.D., Susan Male Smith, M.A., R.D.Tomatoes: Natural Weight-Loss Food. Discovery Fit & Health. http://health.howstuffworks.com