Recent studies on the benefits of eating walnuts have made nutrition headlines: a reduction in the risk of prostate cancer (in mice) and slower growth of breast cancers (also in mice). These unfortunate mice have been bred or treated to develop these particular cancers. Researchers say that it is too soon to draw conclusions for humans from these studies. However, there are several other good reasons to include walnuts in your daily diet. Walnuts, flax seeds, and to a lesser extent canola oil (buy organic forms of this oil) contain relatively high amounts of an omega-3 fatty acid called ALA (alpha-linolenic acid). ALA is a plant precursor to the EPA and DHA found in fish oil. Green leafy vegetables, exclusively grass-fed animals, seeds such as pumpkin seeds and a vegetable known as purslane also have ALA. ALA is converted to EPA and DHA in our bodies, although the conversion is incomplete. Omega-3 fatty acids, from fish and plant sources, are essential for the human brain and body. Besides its ALA content, walnuts have other health benefits which are under investigation. Read on!
No Weight gain: walnut consumption, even in sizable amounts, has not led to significant weight gain. A recent study from Loma Linda School of Public Health asked subjects (but not a control group) to add 1/3 of a cup of walnuts (~280 calories) to their daily food intake. They were given no other dietary guidelines. Participants showed no greater weight gain than the control group over a 6 month period. They ate slightly less food when adding the walnuts, in a voluntary manner. Similar findings have been seen among people who regularly eat other nuts. Nuts lead to satiety, and may make it easier to ignore candy, cake and other empty calories.
Preventing Heart Disease Another Loma Linda study looked at people with moderately high cholesterol levels; when they added slightly less than 1/3 cup of walnuts to their usual diet, their total cholesterol and triglyceride levels decreased significantly. Subjects with the highest baseline readings improved the most. Men with elevated levels of lipoprotein(a) showed a significant decrease in this protein; lipoprotein(a) may increase the risk of heart attack. Another Loma Linda study contrasted the effects of walnuts and fatty fish (fish contain the omega-3 fatty acids DHA and EPA). The fish diet – 2 weekly servings of 4 oz of salmon – decreased triglycerides and increased HDL (good cholesterol) more than the control diet or walnut diet. The walnut diet, adding 1/3 cup of walnuts 6 days a week – showed better effects on LDL cholesterol, and lipoprotein(a). The authors concluded that including walnuts and fatty fish in the diet was helpful in decreasing the risk of heart disease. (While fresh or frozen salmon has become very expensive, you can still find wild-caught Alaskan salmon in cans for about $4.00. Get the unsalted kind if possible.) Researchers at the University of Barcelona have recently shown that in addition to lowering cholesterol, walnuts can improve the elasticity of the arteries, allowing blood to flow more easily throughout the body. This is an important finding.
Melatonin in walnuts Melatonin is the hormone secreted by the pineal gland, behind our eyes, that regulates our sleep-wake cycle. Darkness causes its levels to rise, and bright light inhibits it. As we get older, our nighttime melatonin levels wane, making it harder to fall asleep or stay asleep. Melatonin also acts as an anti-oxidant that helps the body resist toxic molecules called free radicals. Free radicals, that can damage DNA, are thought to be important in aging, cancers, brain disease et al. Melatonin is made by plants as well as animals and is fairly abundant in walnuts. Researchers at the University of Texas in San Antonio found that when laboratory rats were fed walnuts, their blood levels of melatonin went up, as did the total antioxidant capacity of their blood. The researchers surmised that the combination of melatonin and omega-3 fatty acid in walnuts made these nuts unusually beneficial. I surmise that walnuts may be a perfect bedtime snack, and an easy food to have by your bedside when the dreaded two a.m. insomnia makes your world look impossible. Dried tart cherries are said to have a similar helpful effect on sleep, again due to their melatonin content.
Sadja Greenwood, MD, MPH back issues on this blog