Walnuts are a good source of alpha-linolenic acid (an omega-3 fatty acid), as well as numerous phytosterols, polyphenols and carotenoids, and soluble fiber. Walnuts are also a dietary source of selenium, copper, vitamin E and melatonin. Walnuts have the highest total phenolic content, flavonoid content, and antioxidant activity of the nuts commonly consumed in the U.S. Walnut consumption is associated with reduced risks of coronary vascular disease, type 2 diabetes, and blood clot formation, and has been shown to lower cholesterol. Despite the high caloric and fat content of nuts, adding a moderate amount of nuts to the diet has been shown not to result in weight gain. Walnut extract has been shown to reduce the proliferation of liver cancer and colon cancer cells in a dose-dependent manner. Ellagic acid, a major antioxidant component of walnuts, has been found to inhibit cell growth and induce apoptosis in cervical cancer cells.
Breast cancer-related effects of eating walnuts
Consumption of alpha-linolenic acid is associated with reduced breast cancer risk. Walnuts are the best source of this plant-derived omega-3 fatty acid. Walnut consumption has been shown in several studies to significantly reduce breast tumor incidence and size in laboratory mice. For example, one study reported that a diet including walnuts reduced the tumor size produced by triple negative (ER-/PR-/HER2-) breast cancer cells injected into mice.
Walnut oil has a high content of essential fatty acids and we would recommend it. However, walnuts should be consumed in moderation since they contain some copper (approximately 0.45 mg per ounce), which can promote angiogenesis. While copper is a vital nutrient, women with breast cancer should not exceed the RDA (recommended daily allowance) of approximately 0.9 mg.
Refined walnut oil contains essentially no copper. Cold pressed walnut oil is made from nuts that are dried and then cold-pressed, preserving their nutrient content. However refined cold pressed oil is best since refining helps eliminate copper. Walnut oil should be refrigerated and is best used at room temperature (e.g. in salad dressings).
Pecans are related to walnuts but do not have the favorable omega-3 fatty acid profile of walnuts. Pecans contain approximately 0.34 mg copper per ounce.
Below are links to recent studies concerning this food. For a more complete list, including less recent studies, please click on walnuts.