Walnuts resemble both the human head (skull and brains) and prostate, and are a prime example of what ancient herbalists called 'the doctrine of signatures': namely, herbs or foods that resemble various parts of the body can be used to treat ailments of that part of the body. In fact, the 17th-century herbalist William Coles, author of The Art of Simpling and Adam in Eden, stated that walnuts were good for treating head ailments because "they Have the perfect Signatures of the Head."
Nutritional science now confirms walnuts contain nutrients that are necessary for healthy brain function, such as omega-3 fatty acids and vitamin E; but even more compelling clinical research has emerged in only the past four years showing that walnut consumption reduces biomarkers of prostate cancer in humans, and suppresses prostate cancer tumor growth in the animal model. Other cancers walnuts have been studied to suppress include breast and colorectal.
Walnuts also provide great support for brain health, considering the brain is composed of approximately 30% omega-3 fatty acids (DHA, primarily) and require vitamin E and related fat-soluble antioxidants readily found in walnuts to prevent oxidation (rancidity).
Clinical research also now exists on the brain-enhancing effects of walnuts. In aged animals, moderate dietary walnut supplementation improves cognitive and motor performance. Another human studied published in the British Journal of Nutrition in 2011 showed that walnut consumption increases inferential reasoning in college students.
For additional information on the nutritional and medicinal properties of walnut visit NutritionData.com and GreenMedInfo.com's walnut page.