One easy way to boost your immune system is to get to know seven produce powerhouses - seven amazing greens that deserve a spot in your crisper and in your diet. "Most people use the same rotation of lettuce and spinach," says Andrea Giancoli, RD, a spokesperson for the Academy of Nutrition and Dietetics, "so they miss out on some of the tastiest, most nutritious vegetables."

In the June, 2012 FITNESS Magazine, author Sharon Liao introduces us to these greens and even tells how to best prep them for daily use. Following is her "guide to greens."

Collard Greens: They resemble wide, flat cabbage leaves. Look for a deep green hue. Research shows that this mild green is better at lowering artery-clogging cholesterol than broccoli or spinach.

They are traditionally cooked with pork fat, but try a lighter approach instead: Remove the stems and slice the leaves into two-inch pieces; meanwhile, fry turkey bacon in olive oil. Crumble bacon and sauté it with the collards and garlic. Add enough chicken stock to just cover the greens, reduce the heat to low, and simmer for an hour, or until tender. "Cooking collards for a long time breaks down the tough fibers," says Aliza Green, a chef in Philadelphia and the author of Field Guide to Produce. Finish the dish with a splash of apple cider vinegar and red pepper flakes.

Kale: Curly kale is deep green with ruffled edges. Tuscan kale, aka dinosaur or black kale, has bumpy blue-green leaves. It is sweeter in winter, but it's packed with nutrients year-round. Just one cup of raw kale supplies a day's worth of vitamins A and C and six times the daily requirement of bone-boosting vitamin K.

A tasty idea is to make snacking chips: Strip the leaves off the tough, inedible stems and tear them into 1 3/4-inch pieces. Toss with olive oil and salt and bake at 350°F for 10 to 15 minutes, or until crispy. For a simple no-cook side dish, slice kale into one-inch ribbons, add a tablespoon each of olive oil and lemon juice and a dash of salt; then gently massage with your fingertips until the leaves are wilted. Top with freshly ground black pepper, nuts or seeds for crunch, and either avocado slices or a sprinkle of pecorino.

Turnips: Avoid wilted or yellow leaves, or any that have slick dark green patches. When cooking, save the tops, which have a strong flavor and cabbage-like texture. "They're loaded with fiber and vitamin K," says Maggie Moon, RD, a nutritionist for the New York City-based online grocer FreshDirect. One cup of the cooked greens fulfills 20% of the daily requirement for vitamin B6.

Blanching turnip greens softens their "bite." Sauté the sautéed greens in olive oil with garlic and finish with a little lemon juice or apple cider vinegar. Or sauté garlic, onion, and lemon zest in olive oil; add turnip greens and white wine and simmer until soft. Then puree in a blender and serve as a dip with crusty bread.

Bok Choy: Choose thick, firm stalks with bright leaves. Bok choy is also called Chinese cabbage or pak choi. This mild, slightly sweet cousin of cabbage is a super source of calcium because it's low in oxalate, a compound in many greens that blocks absorption of the mineral. It also has 25 kinds of cancer-fighting antioxidants called polyphenols.

Small, tender baby bok choy is great in stir-fries or tossed with oil, salt, and black pepper and roasted at 400°F for five minutes. If you're cooking the regular-size kind, make a side dish by chopping the stalks and sautéing them in oil with garlic, ginger, and reduced-sodium soy sauce for three to four minutes. Then add the greens a few minutes before serving, so that the stalks are tender and the leaves are just wilted.

Watercress: The small, oval-shaped leaves should smell peppery. Watercress is loaded with vision-protecting carotenoids and compounds that inhibit the growth of breast cancer tumors.

Trim stems, then add the leaves to sandwiches, frittatas, and salads. It's really nice paired with a sweet balsamic vinaigrette. Or use it as a lovely garnishing bed - use fresh leaves as a bed for roast chicken or beef. To make soup, sauté a cubed potato and a diced onion, then simmer them in two cups each of low-fat milk and chicken stock for 10 minutes, or until tender. Add two cups of watercress (leaves and stems), cook five minutes more, and puree until smooth. Garnish with fresh watercress leaves and low-fat sour cream.

Swiss Chard: Eye-popping red, yellow, orange, or white stalks signal freshness. This somewhat salty relative of the beet is a top source of vitamins A and C. And one cup of cooked Swiss chard delivers more than 20% of your daily quota for iron.

Both the stalks and the leaves are edible. To soften the leaves, blanch them for a few minutes; then sauté with olive oil and garlic and toss with golden raisins. Or wrap seasoned fish fillets in the blanched leaves and bake. For a side dish, cook the stalks, then chop each into three or four pieces and boil in water with a squeeze of lemon juice for five minutes. Toss with olive oil and Parmesan; then broil for 10 minutes.

Escarole: You want tightly packed unblemished leaves. It looks like romaine, but unlike romaine, it has a firm texture, paler color, and slightly bittersweet taste. At just eight calories per uncooked cup, this nutrition superstar supplies fiber and heart-healthy folate, along with vitamins A, C, and K.

The inner leaves are sweet and mild, so they work well in salads. To prep, use a paring knife to cut off a thin slice on the stem end, then remove the core. Toss with olive oil, lemon juice, salt, and pepper and top with shaved Parmesan. The outer leaves provide nice texture and flavor when added to minestrone and turkey chili.

Now, here are author Liao's 5 tips for easy and smart prepping that will make greens last to final leaf:

STEP 1: Trim by chopping off the stems, or slicing out the core, if there is one. Then tear apart the leaves, discarding any that are brown or bruised.

STEP 2: Wash to remove sand from sturdy greens, such as kale and collards, put them in a large bowl or clean sink filled with cold water. Swish vigorously to loosen grit, then scoop out the leaves; dirt will sink to the bottom. For delicate leaves, like watercress or bok choy, simply rinse carefully under running water.

STEP 3: Dry them using a salad spinner, or spread a single layer of leaves on a clean towel. You want them only slightly damp, or they'll wilt.

STEP 4: Refrigerate next. Roll up the towel and place it in a plastic produce bag from the grocery store; if you used a spinner, put dry leaves directly in the bag. Store greens in the crisper drawer, away from fruit. Certain fruits, like apples, pears, and avocados, emit ethylene, a gas that can hasten spoilage.

STEP 5: Revive if needed. Although greens should last up to a week in the fridge, they may wilt. To perk them up, place them in a bowl of ice water for 15 minutes.

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Sources:
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www.wisegeek.org
www.pacridgefarms.com