This is the third installment in an occasional series on the health benefits of nuts. However, for this particular column we're going to fudge it a little as peanuts are really legumes and more like beans than nuts.

Why: Peanuts are impressive nutrient powerhouses — they have more than 30 essential nutrients and phytonutrients. They're unusual because the peanut flowers above the ground but its fruits are below the ground. Whether shelled or unshelled, peanuts are usually dry-roasted. Raw peanuts would taste like a bitter, soft bean, and the roasting process also helps to kill the naturally occurring bacteria associated with being grown in the dirt.

Dry roasting is a process by which the peanuts are placed in an oven and subjected to forced hot air for about 15 minutes. They may be plain-roasted or seasoned and roasted in the shell. "To season peanuts in the shell, they are washed prior to roasting. After that, the seasonings, which are dissolved in water, are forced through the shells by a pressure process. Then, when the peanuts are dried during roasting, the seasonings remain inside the shells," says Lisa Agostoni, a spokeswoman for the National Peanut Board.

Peanuts can also be oil-roasted in cookers that take a steady stream of peanuts through hot oil for about five minutes.

There are several types of peanuts — runner, Spanish, Valencia and Virginia. Almost 80 percent of the peanuts produced in the United States are runner, with most used to make peanut butter. Spanish peanuts, recognized by their reddish-brown seed cover and extra-nutty flavor, are smaller and used in cooking, peanut candies and to make peanut oil (because of their high oil content). Valencia peanuts are very sweet and typically roasted in the shell. They're unique because they can have three or more kernels, each enclosed in a bright-red skin, inside every shell. The peanuts sold in stadiums and at the circus are the Virginia variety.

Nutrients: (Daily values are based on 1 ounce) Peanuts are a good source of vitamin E (11 percent of daily values), which is known to have antioxidant properties and to boost immune function, and folate (10 percent daily values), widely known for its role in reducing the risk of certain serious birth defects, such as spina bifida. They also contain 2 grams of fiber, which is good for digestive health and increased feelings of satiety; niacin (19 percent of daily values), which helps reduce high cholesterol; magnesium (12.5 percent of daily values), which relaxes muscles and increases metabolism; phosphorus (10 percent of daily values), for healthy bones and teeth; copper (9.5 percent of daily values), to help convert carbs into energy; and good amounts of potassium, zinc, iron and heart-healthy mono- and polyunsaturated fats. Just 1 ounce of peanuts also has about 7 grams of protein, more than any other nut. Protein helps keep you feeling full longer. Peanuts also contain high amounts of arginine (an amino acid that can improve blood flow) and flavonoids (antioxidants that reduce inflammation and protect against cell damage). Plus, they're low in sodium, and like any plant-based food, naturally cholesterol- and trans fat-free.

Health Perks: Peanuts contain resveratrol, linked to a reduced risk of cardiovascular disease and cancer. They are also very low on the glycemic index, which means that they do not cause a rapid rise in blood sugar, and there has been research demonstrating that they may help prevent diabetes.

Nutrition Stats: (1 ounce, 30 peanuts) 166 calories, 14g fat, 230mg sodium, 6.1g carbs, 2.3g fiber, 6.71g protein.

Purchasing: "Look for things such as moisture or shell texture. Unlike a melon, you can't squeeze a peanut to tell if it's ripe, but you can inspect the shell to make sure it's not broken or soggy," Agostoni says.

Storage: Peanuts have a short shelf life, mostly because of the high percentage of oil they contain, and high temperatures may cause their fat to become rancid. Stored sealed, in a dry place below 70 degrees, they will probably last a week. They last longer when refrigerated, and you can freeze them indefinitely.

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.