1. Walnuts

When it comes to nuts, the walnut is the king. It's a great source of the healthy omega-3 essential fatty acids, which have been found to protect the heart, promote better cognitive function, and provide anti-inflammatory benefits for asthma, rheumatoid arthritis, eczema and psoriasis.

Walnuts also contain the antioxidant compound ellagic acid, which is known to fight cancer and support the immune system. But that's not all--in a study in the August 2003 issue of Phytochemistry, researchers identified 16 polyphenols in walnuts, including three new tannins, with antioxidant activity so powerful they described it as "remarkable."

Walnuts are incredibly healthy for the heart. A study in the April 2004 issue of Circulation found that when walnuts were substituted for about one-third of the calories supplied by olives and other monounsaturated fats in the Mediterranean diet:

• Total cholesterol and LDL (bad) cholesterol were reduced

• The elasticity of the arteries increased by 64 percent

• Levels of vascular cell adhesion molecules, which play a major role in the development of atherosclerosis (hardening of the arteries), were reduced

2. Almonds

Just a quarter cup of almonds contains nearly 25 percent of your needed daily value of the important nutrient magnesium, plus is rich in potassium, manganese, copper, the antioxidants vitamin E and selenium, and calcium. In fact, a quarter cup of almonds has almost as much calcium as a quarter cup of milk.

They're also great for the colon. An animal study on the effects of almonds on colon cancer found that animals (which were exposed to a colon-cancer-causing agent) given whole almonds had fewer signs of colon cancer than animals given almond oil or no almonds. Researchers suspect the benefit may be due to almonds' high fiber content.

Plus, almonds are one of the best nuts for lowering cholesterol because 70 percent of the fat they contain is the healthy monounsaturated variety, which has been shown to help clear arteries.

3. Cashews

Cashews are lower in fat than most nuts, and 65 percent of this fat is unsaturated fatty acids. Of this, 90 percent is oleic acid, the heart-healthy fat found in olive oil.

Plus, cashews are rich in copper, magnesium, zinc, iron and biotin.

4. Pecans

Pecans are an excellent source of over 19 vitamins and minerals including vitamins E and A, folic acid, calcium, magnesium, copper, phosphorus, potassium, manganese, several B vitamins and zinc.

Plus, according to Sue Taylor, R.D., director of nutrition communication for the National Pecan Shellers Association, "Recent clinical research studies evaluating the impact of pecans on serum cholesterol have found pecans can significantly help lower blood cholesterol when consumed as part of a heart-healthy diet."

In fact, a study from New Mexico State University found that eating 3/4 cup of pecans a day may significantly lower LDL (bad) cholesterol and help to clear the arteries.

5. Brazil Nuts

These nuts are extremely nutrient-rich and contain protein, copper, niacin, magnesium, fiber, vitamin E and selenium. Selenium is a powerful antioxidant that works to neutralize dangerous free radicals. A study at the University of Illinois even found that the high amounts of selenium in Brazil nuts may help prevent breast cancer.