Walnuts may help reduce not only the risk of prostate cancer, but breast cancer as well. In one study, mice that ate the human equivalent of 2.4 ounces of whole walnuts for 18 weeks had significantly smaller and slower-growing prostate tumors compared to the control group that consumed the same amount of fat but from other sources.
Overall the whole walnut diet reduced prostate cancer growth by 30 to 40 percent. According to another study on mice, the human equivalent of just two handfuls of walnuts a day cut breast cancer risk in half, and slowed tumor growth by 50 percent as well.1
Walnuts contain the amino acid l-arginine, which offers multiple vascular benefits to people with heart disease, or those who have increased risk for heart disease due to multiple cardiac risk factors.
If you struggle with herpes, you may want to avoid or limit walnuts, as high levels of arginine can deplete the amino acid lysine, which can trigger herpes recurrences.
Walnuts also contain the plant-based omega-3 fat alpha-linolenic acid (ALA), which is anti-inflammatory and may prevent the formation of pathological blood clots. Research shows that people who eat a diet high in ALA are less likely to have a fatal heart attack and have a nearly 50 percent lower risk of sudden cardiac death.2
Eating just four walnuts a day has been shown to significantly raise blood levels of heart-healthy ALA,3 and walnut consumption supports healthful cholesterol levels.
Separate research showed that eating just one ounce of walnuts a day may decrease cardiovascular risk,4 and among those at high cardiovascular risk, increased frequency of nut consumption significantly lowers the risk of death.5
Rare and Powerful Antioxidants
Antioxidants are crucial to your health, as they are believed to help control how fast you age by combating free radicals, which are at the heart of age-related deterioration.
Walnuts contain antioxidants that are so powerful at free-radical scavenging that researchers called them "remarkable,"7 and research has shown that walnut polyphenols may help prevent chemically-induced liver damage.8
In another study, researchers found that nuts, especially walnuts, have potent antioxidant powers. Walnut polyphenols had the best efficacy among the nuts tested and also the highest lipoprotein-bound antioxidant activity. The researchers concluded:9
"Nuts are high in polyphenol antioxidants which by binding to lipoproteins would inhibit oxidative processes that lead to atherosclerosis in vivo. In human supplementation studies nuts have been shown to improve the lipid profile, increase endothelial function and reduce inflammation, all without causing weight gain."
Adding healthful amounts of nuts such as walnuts to your diet can help you to maintain your ideal weight over time. In one review of 31 trials, those whose diets included extra nuts or nuts substituted for other foods lost about 1.4 extra pounds and half an inch from their waists.10 Eating walnuts is also associated with increased satiety after just three days.11
Improved Reproductive Health in Men
One of the lesser-known benefits of walnuts is their impact on male fertility. Among men who consume a Western-style diet, adding 75 grams (a bit over one-half cup) of walnuts daily significantly improved sperm quality, including vitality, motility, and morphology.12
Walnuts contain a number of neuroprotective compounds, including vitamin E, folate, melatonin, omega-3 fats, and antioxidants. Research shows walnut consumption may support brain health, including increasing inferential reasoning in young adults.13
One study also found that consuming high-antioxidant foods like walnuts "can decrease the enhanced vulnerability to oxidative stress that occurs in aging," "increase health span," and also "enhance cognitive and motor function in aging."14
The beneficial dietary fat in walnuts has been shown to improve metabolic parameters in people with type 2 diabetes. Overweight adults with type 2 diabetes who ate one-quarter cup of walnuts daily had significant reductions in fasting insulin levels compared to those who did not, and the benefit was achieved in the first three months.15