From Jennifer Moll,
Your Guide to Cholesterol.
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About.com Health's Disease and Condition content is reviewed by Rich Fogoros, MD

Walnuts are not only good for cooking, but they may help your heart. Food and Drug Administration (FDA), recognizing the cholesterol-lowering properties of walnuts, accepted a petition filed by the California Walnut Commission in March 2004 to list the health claim that walnuts can aid in reducing cholesterol levels. Through many studies performed by various research institutions all over the world, the benefits of walnuts have now been discovered. Not only has the consumption of walnuts proven beneficial in lowering cholesterol levels, they have been also noted to reduce the risk of heart disease and inflammation.

What makes walnuts so healthy?
The reason that walnuts demonstrate such heart healthy benefits is because of the presence of high amounts of omega-3-fatty acids, particularly alpha linoleic acid, and phytosterols. Omega-3-fatty acids reduce triglycerides levels and reduce the formation of atherosclerotic plaque on arteries by increasing HDL levels (high density lipoproteins, or the good cholesterol) and reducing LDL levels (low density lipoproteins, also know as the bad cholesterol). Phytosterols appear to lower total cholesterol levels, however, the mechanism by which it does this is not entirely known. In fact, walnuts contain the highest amount of omega-3-fatty acids in 1 ounce of nuts (i.e. one handful) in comparison to other nuts (2.5 g of omega-3-fatty acids versus less than 0.5 g found in other nuts).

In addition to heart healthy ingredients, walnuts also contain a wealth of other nutrients, including vitamin E, the B vitamins, fiber, and several minerals. Many of the studies performed suggest that you only need to consume only a handful of walnuts a day to receive the cholesterol-lowering benefits of walnuts. The FDA agrees with this health claim, which will be on every bag of walnuts you purchase and will state the following: "supportive but not conclusive research shows that eating 1.5 oz of walnuts per day, as part of a low saturated fat and low cholesterol diet, and not resulting in increased caloric intake may reduce the risk of coronary heart disease. See nutrition information for fat [and calorie] content."

Where’s the proof?
Many studies have indicated the usefulness of walnuts in reducing cholesterol levels. The first study involving the benefits of walnuts was performed at Loma Linda University in 1993 (NEJM 328:603-7). This study revealed a controlled diet containing walnuts reduced LDL cholesterol significantly in comparison to the Step One diet produced by the American Heart Association. The controlled diet was a modified version of the Step One diet, with the exception that walnuts replaced the fatty acid portion in the diet. A Harvard study outlining the benefits of nuts concluded that high dietary nut consumption decreased the risk of sudden cardiac death in 2002. In addition to this, many studies have elucidated the benefits of consuming walnuts and other omega-3 fatty acid-containing foods, citing that consuming high amounts of these products reduced the risk of stroke and clogging of arteries up to 70% (Stroke 26:778-82). These results were first published in Lancet in 1994 (343:1454-9), and then subsequently published in reputable journals, such as Preventative Medicine (28:333-9), American Journal of Clinical Nutrition (74:72-9), and Annals of Internal Medicine (132(7):538-46).