Research & Education

New Role for Walnuts

Walnuts are a delicious and healthy snack and they make a great addition to sweet as well as savory dishes. But this nut’s benefits aren’t limited to culinary applications. Walnut-rich diets may be helpful in the fight against cancer through multiple mechanisms.

Like most other nuts walnuts are low in carbohydrates and high in minerals and unsaturated fats. They’re a good source of manganese copper and magnesium and compared to most other nuts walnuts contain a fair amount of omega-3 alpha-linolenic acid (about 2.5g/ounce). In fact this is the highest amount of any tree nut. They are high in omega-6 linoleic acid as well (about 10.6g/ounce) but they stand out among other nuts in that most others contain very little omega-3 to balance that out.      

Researchers have found that the omega-3s phytosterols and antioxidants in walnuts all may be especially beneficial for colon cancer. In a mouse model of colon cancer mice fed the human equivalent of two servings of walnuts a day showed significantly reduced colorectal tumor growth largely resulting from reduced angiogenesis. Researchers believe microribonucleic acids (miRNAs) may help explain the relationship between walnut consumption and disease risk. miRNAs are short noncoding RNAs (21–25 nucleotides) that play a role in regulating posttranscriptional gene expression affecting the stability and translation of messenger RNA. miRNAs may mediate cellular differentiation development and apoptosis and may act as an oncogene under certain conditions. Inhibition of some types of miRNA activity is associated with reductions in tumor growth angiogenesis metastasis and enhanced tumor suppression in animal models of colorectal cancer. 

Researchers determined that the walnut-rich diet led to higher incorporation of n-3 fats into the cell membrane of colorectal tumor cells which decreased expression of inflammatory cytokines leading to slower proliferation and increased apoptosis of cancerous cells. The colorectal tumors of walnut-fed mice contained significantly more total n-3 than the tumors of untreated mice including ALA but also EPA and DHA suggesting that some of the ALA was elongated into the longer-chain fatty acids. This study showed a negative association between final tumor size and the total tissue concentration of omega-3 fatty acids and an individual association with concentrations of DPA EPA and DHA. These fatty acids may play a role in managing tumor size by affecting signaling involved in cellular proliferation and tissue vascularization.

The potential influence of walnuts on cancer isn’t solely due to its fatty acid composition. Researchers speculate that the phytosterol sitosterol in walnuts may affect apoptosis and initiate arrest of cell proliferation. Walnuts also contain γ-tocopherol which may result in tumor growth suppression by upregulating PPAR activity and reducing angiogenesis. “Activated PPAR-γ signals antiproliferative antiangiogenic and prodifferentiation pathways in multiple tissue types.” β-Sitosterol has demonstrated pro-apoptotic effects and an ability to arrest the first stage (G1) of cellular proliferation.

Other studies support a protective role for walnuts as a whole food as opposed to isolated omega-3 fats lending more evidence to synergistic effects of multiple compounds in walnuts beyond the known effects of n-3s. “Mouse studies in which walnuts were added to the diet have shown the following compared with the control diet: 1) the walnut-containing diet inhibited the growth rate of human breast cancers implanted in nude mice by ∼80%; 2) the walnut-containing diet reduced the number of mammary gland tumors by ∼60% in a transgenic mouse model; 3) the reduction in mammary gland tumors was greater with whole walnuts than with a diet containing the same amount of n–3 fatty acids supporting the idea that multiple components in walnuts additively or synergistically contribute to cancer suppression.”

The combined effects of multiple compounds in walnuts support a role for this whole food in the fight against cancer—one that might not be achievable through administering isolated individual substances. Nutritional and nutraceutical supplements have their place in maintaining optimal health and sometimes nature can also package nutrients together just right.