Artists used to rely on walnut oil as a drying agent for paint because its slow drying time allowed for even application over a broad surface. The oil would form a solid film after long exposure to air, rendering colors rich and luminous with its translucency. In fact, Michelangelo even used walnut oil while painting the Sistine Chapel.

Walnut Date Muffins
Spiced Walnuts

Depending on how you split a walnut in its shell, the nut resembles either a heart or a brain -- and how apt, since these nuts do wonders for both.

Although walnuts boast heart-healthy oil like most nuts, they have an added edge. Most nut oil is monounsaturated, but walnuts primarily contain the polyunsaturated variety. In fact, they're the only nuts -- and one of the few foods -- that offer appreciable amounts of a crucial type of polyunsaturated fat called alpha-linolenic acid, or ALA, which is an omega-3 fatty acid. ALA protects the heart in several ways: It improves your ratio of HDL (good) to LDL (bad) cholesterol, and it reduces inflammation, helping to block the conversion of cholesterol into harmful, artery-clogging plaque. ALA also plays a significant role in the development of the brain and cognitive function; low levels of ALA have been associated with depression and other mood disorders.

Since your body can't manufacture ALA, you need to eat foods that contain it. Studies show that most people consume less than the recommended daily amount (1.1 g to 1.6 g). Walnuts fit the bill, but they're also high in calories, so don't go overboard. Think in terms of a handful: An ounce of walnuts, or about one-quarter cup, provides 2.6 g of ALA (and 185 calories).

The benefits of eating walnuts extend even beyond the good fat. They provide a concentrated source of disease-fighting antioxidants, including gammatocopherol, a type of vitamin E. They also have ellagic acid, a compound with anticancer properties, and melatonin, which helps regulate sleep patterns and delay age-associated diseases like Parkinson's and Alzheimer's. The protein in walnuts contains the amino acid arginine, which relaxes blood vessels (good for high-blood pressure), helps inhibit tumor growth, and boosts immunity.

Two main types of walnuts grow in the United States: the pungent, tough-to-crack black walnut and the Persian (often called English) walnut that you'll encounter in most supermarkets. Because of their high polyunsaturated fat content, walnuts are more perishable than other nuts. Buy from sources with a good product turnover, and choose nuts that are still in the shell if possible. If you do buy shelled walnuts, go for the halves rather than the pieces (more cut surfaces encourage oxidation). Store them in the refrigerator or freezer to maximize freshness. Spread walnuts on a baking sheet and toast them for 8 to 10 minutes in an oven heated to 350 degrees just before using to bring out their flavor.

Looking for another way to get more walnuts into your diet? Try walnut oil, available as either refined or unrefined. Oil that is cleaned after pressing to remove any unwanted odors and flavors is refined. Its unassuming taste -- and the fact that it can be heated up to 400 degrees -- make it an excellent oil for sauteing. Unrefined walnut oil is more expensive, more perishable, and more susceptible to heat than refined walnut oil. Made from nuts roasted at a moderate temperature before pressing, it has a nutty taste and a light brown color. Because unrefined oil has a lower smoke point of 320 degrees, you shouldn't heat it. Instead, use it in salad dressings or baked goods, or drizzle it on finished dishes.

Text by Cheryl Redmond; recipes by Sandra Gluck