Shopping for vegetables at my local farm shop this morning, my eyes lit on an unexpected find: wet walnuts! "Walnuts - already?!" I exclaimed, realizing with a pang that fall is imminent.
Before I had a chance to lament the passing of summer with its juicy peaches, sun-ripened tomatoes and chilled cucumber soups, I succumbed to the charms of those juicy golden kernels whose season lasts only a week or three. I rushed home with my brown paper bag of fresh walnuts, dug around for the nutcracker that had slumbered for months at the back of my kitchen drawer and got cracking.
When they are this fresh - their shells cool and damp, the kernels so moist they melt in your mouth - walnuts are simply amazing. They have a creamy, sweet flavor and lack the mouth-puckering bitterness of their aged counterparts. Paired with spicy farmhouse cheddar, chopped and sprinkled over oatmeal or fresh applesauce or simply on their own they make a delectable snack.
Even if you can't lay your hands on fresh walnuts - few supermarkets sell them as they are prone to molding - they are just as delicious dried. And in addition to their gastronomic appeal, walnuts are a nutritional powerhouse with cancer-protective qualities thanks to their high content of omega-3 fatty acids and antioxidants.
With impeccable timing, a new animal study in the journal Nutrition and Cancer and jointly funded by the American Institute for Cancer Research and the California Walnut Commission (according to the study's authors, neither funding agency had input on the design, collection or interpretation of the data) has found that eating walnuts may reduce the risk of breast cancer.
The study compared the effects of a typical American diet - among others, rich in cancer-promoting omega-6 fatty acids - to that of a diet containing walnuts across the lifespan: Through the mother from conception through weaning, and subsequently by eating the food directly. The amount of walnut in the test diet equated to about 2 ounces (or 28 walnut halves) a day for humans.
"We found that consumption of a walnut diet reduced mammary tumors in mice," said W. Elaine Hardman, PhD, the study's lead investigator and associate professor at the Marshall University's Joan C. Edwards School of Medicine. "The best tumor reduction was when both the mother consumed walnuts and her offspring consumed walnuts throughout life."
For the study, a test group of female mice genetically predisposed to breast cancer was fed a diet containing ground walnuts. The offspring whose diets also included walnuts developed breast cancer at less than half the rate of the group consuming no walnuts. In addition, the number of tumors and their sizes were significantly smaller.
A second group of mice fed walnuts only after weaning (their mothers did not eat walnuts during gestation) were less well-protected, but nonetheless showed approximately one-third fewer tumors compared to the mice not exposed to walnuts at all. A third group of mice whose only source of fat was corn oil - rich in omega-6 fatty acids - experienced the fastest tumor developments.
Walnuts' main nutritional appeal has long thought to lie in its beneficial omega-6-to-3 ratio (about 4:1, close to the 3:1 ratio considered ideal for human health; by comparison, the omega 6-to-3 ratio for corn oil is around 50:1). Walnuts contain the highest fraction of omega-3-rich alpha-linolenic acid of all tree nuts, and omega-3s have been shown previously to slow cancer growth.
But walnuts' anti-cancer effects aren't just limited to omega-3s. Additional cancer-protective compounds in walnuts include vitamin E (especially gamma tocopherol, associated with slowing cancer cell growth), ellagic acid (an antioxidant present in various nuts and fruits that encourages the self-destruction of cancer cells) and phytosterols, plant compounds with a range of cancer-inhibiting mechanisms.
"With walnuts, as with other foods, it is likely the synergism between the components that leads to reduced cancer incidence," said Hardman.
Another piece of good news: although they are rich in calories, the addition of a moderate amount of walnuts to the diet does not appear to cause weight gain in humans, according to this study.
But before you, too, rush out to buy a bag of walnuts, a few caveats. Because of their high omega-3 content, walnuts can easily go rancid if stored incorrectly. (Rancid walnuts smell like paint thinner; if this happens, throw them away.) Protect them from heat, light and oxygen (buy them vacuum-packed and store in the refrigerator - or better still, buy them whole, store in a cool, dark place and crack them yourself.) It's fine to bake muffins or fruit loaves with chopped walnuts, but avoid toasting them in a pan or a hot oven as this can damage their fragile oils. When buying walnut oil, always choose the smallest bottle you can find, refrigerate and use up quickly.
In Zest for Life I have included a recipe for walnut Tarator, a garlicky-herby paste of ground walnuts from Turkey that can be enjoyed as dip, diluted with yogurt and water to make a chilled summer soup, or spooned onto hot pasta. The California Walnut Commission's website provides a multitude of other recipes (avoid the ones that contain large amounts of sugar). Enjoy!
Copyright Conner Middelmann-Whitney. Conner is a nutritionist, health writer and health-cookery instructor. She recently published Zest for Life, The Mediterranean Anti-Cancer Diet, a cancer-prevention nutrition guide and cookbook anchored in the traditional Mediterranean diet (available at Amazon, Barnes & Noble and other online bookstores). Conner offers nutrition consultations via Skype; please consult her website for details.