Walnuts are recommended for breast cancer

Walnuts have the highest total phenolic content, flavonoid content, and antioxidant activity of all nuts commonly consumed in the U.S. Walnuts are a good source of alpha-linolenic acid (ALA, an omega-3 fatty acid), β-sitosterol, ellagic acid, pedunculagin, melatonin, and urolithin A, all of which have proven or suspected chemopreventive properties. Walnuts are also a dietary source of copper. 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 their high caloric and fat content, 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 has been found to inhibit cell growth and induce apoptosis (programmed cell death) in cervical cancer cells.
Consumption of ALA is associated with reduced breast cancer risk. Walnuts are the best source of this plant-derived omega-3 fatty acid. ALA is converted during metabolism into eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which have been reported to have chemopreventive effects in numerous studies. For example, they have been shown to reduce lung metastasis in a mouse model of breast cancer and to inhibit the early stages of HER2/neu overexpressing (HER2+) breast cancer. However, the conversion of ALA can be blocked in the presence of vegetable oils with high omega-6 fatty acid content such as corn oil, safflower oil, soybean oil, sunflower oil, and grape seed oil. Therefore, walnuts and walnut oil should be consumed separately from such oils.
Walnut extracts and walnut compounds have been shown to inhibit the growth and proliferation of both hormone receptor positive (ER+/PR+) and triple negative (ER-/PR-/HER2-) breast cancer cells. 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 size of tumors produced by injecting triple negative breast cancer cells into mice.
The melatonin in walnuts protects against breast cancer in several ways, for example by reducing aromatase activity within the breast, thereby reducing estrogen production. Melatonin has also been found to be effective in reducing tumor growth, cell proliferation, and angiogenesis in an animal model of triple negative (ER-/PR-/HER2-) breast cancer.
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. 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) rather than in frying.
Pecans are related to walnuts but do not have the favorable omega-3 fatty acid and phenolic profile of walnuts.
Below are links to recent studies concerning this food. For a more complete list, including less recent studies, please click on walnuts.

Intra-tumoral copper modulates PD-L1 expression and influences tumor immune evasion Melatonin as a Radio-Sensitizer in Cancer α-Linolenic acid inhibits the migration of human triple-negative breast cancer cells by attenuating twist1 expression and suppressing twist1-mediated epithelial-mesenchymal transition The Effect of Zinc and Melatonin Administration on Lipid Peroxidation, IL-6 Levels, and Element Metabolism in DMBA-Induced Breast Cancer in Rats Inhibitory effect of melatonin on hypoxia-induced vasculogenic mimicry via suppressing epithelial-mesenchymal transition (EMT) in breast cancer stem cells Legume and Nuts Consumption in Relation to Odds of Breast Cancer: A Case-Control Study Cultivating the gut microbiome by eating walnuts to slow cancer cachexia weight loss Clinical impact of melatonin on breast cancer patients undergoing chemotherapy; effects on cognition, sleep and depressive symptoms: A randomized, double-blind, placebo-controlled trial Usefulness of melatonin as complementary to chemotherapeutic agents at different stages of the angiogenic process The role of melatonin on miRNAs modulation in triple-negative breast cancer cells Melatonin inhibits Warburg-dependent cancer by redirecting glucose oxidation to the mitochondria: a mechanistic hypothesis Histone deacetylase activity and vitamin D‐dependent gene expressions in relation to sulforaphane in human breast cancer cells Development of functional edible oils enriched with pistachio and walnut phenolic extracts Dietary walnut altered gene expressions related to tumor growth, survival, and metastasis in breast Cancer patients: A pilot clinical trial Green Synthesis of Carbon Dots Derived from Walnut Oil and an Investigation of Their Cytotoxic and Apoptogenic Activities toward Cancer Cells Tree nut, peanut, and peanut butter intake and risk of postmenopausal breast cancer: The Netherlands Cohort Study Antioxidant and Anticancer Activities of Walnut (Juglans regia L.) Protein Hydrolysates Using Different Proteases Evaluation of the selective anticancer potential and the genetic mechanisms of the induction of apoptosis by walnut milk in human breast and prostate cancer cells Health Benefits of Walnut Polyphenols: An Exploration beyond Their Lipid Profile Isolation of a novel bio-peptide from walnut residual protein inducing apoptosis and autophagy on cancer cells