Paleo Diet Basics: Why I Eat Walnuts

 

Image Source:  Mariani Nut

Some contemporary hunter-gatherer tribes displaying a high immunity to diseases of civilization consume fairly large amounts of nuts.  Although some nuts richly supply omega-6 fats and an excess intake of corn, soy, or safflower oils rich in these fats may have ill effects, I hesitate to generalize these effects to all whole foods rich in such oils.  Since whole foods contain a myriad of compounds,  I believe that we have to evaluate each food as a whole, not reduce any food to a predominant nutrient.

The !Kung got up to 50% of their calories from the mongongo nut. The mongongo supplies 57 g fat/100g, and 43% of that fat occurs as PUFA, nearly all linoleic acid (omega-6). Assuming 2000 kcal/d and 1/3 of calories as mongongo, they would get ~16g linoleic/d just from the nuts, then some from game fats.

However, a 100g portion of mongongos also provides approximately 193 mg of calcium, 527 mg magnesium, 3.7 mg iron, 2.8 mg copper, 4 mg zinc, 0.3 mg thiamine, 0.2 mg riboflavin, 0.3 mg niacin, and a stunning 565mg of vitamin E.  This very high vitamin E content makes the oil very stable and resistant to oxidation and 'rancidity' for a very long time, in spite of the African heat.

Inland Australian Aborigines consumed considerable amounts of wild walnuts, almonds, candlenut, pine nuts, and even acorns.

I consume fairly large amounts of nuts, particularly walnuts and almonds, more of the former and less of the latter. Walnuts appear to have a number of positive effects on health. I have collected some articles and abstracts of research on the health effects of walnuts. I have not read all of these in full text yet, but a perusal of PubMed shows a clear pattern of independent research on walnuts suggesting significant health benefits.


Cancer Prevention

According to the American Association for Cancer Research, a team led by Elaine Hardman, Ph.D., associate professor of medicine at Marshall University School of Medicine, studied mice that consumed a diet containing the human equivalent of two ounces of walnuts per day. A separate group of mice ate a control diet.

"Standard testing showed that walnut consumption significantly decreased breast tumor incidence, the number of glands with a tumor and tumor size.

'These laboratory mice typically have 100 percent tumor incidence at five months; walnut consumption delayed those tumors by at least three weeks,' said Hardman."

Carvalho et al tested extracts of walnuts for human cancer cell antiproliferative and antioxidant activities. They found that the extract of walnut seed inhibited growth of human renal and colon cancer cells.

Aithal et al found that juglone, a naphthoquinone from walnut, kills cultured melanoma tumor cells.

Spaccarotella et al studied the effects of walnut consumption on prostate and vascular health in men at risk for prostate cancer. The 21 subjects consumed 75g of walnuts daily, replacing other calories in the diet. They found that walnuts may improve biomarkers of prostate and vascular status.

 

Image source:  Pretty Garlic

Cardiovascular Health

Casas-Agustench et al conducted a human trial in which subjects consumed a mix of 15g walnuts with 7.5g almonds and 7.5g hazelnuts daily. Comapred to a control group, those eating the nut mix had a reduction of fasting insulin and insulin resistance.

Ma et al conducted a human trial in which type 2 diabetic subjects consumed with 56 g (366 kcal) walnuts/day for eight weeks. They found that the walnut-consumers displayed a significant improvement in endothelium-dependent vasodilatation, suggesting a potential reduction in overall cardiac risk.


Ros et al had 21 people with high cholesterol consume either a Mediterranean diet or a similar diet in which walnuts replace about 32% of the monounsaturated fat (which amounted to 40-65g walnuts daily, varied as a proportion of caloric intake). They reported that, compared to the Mediterranean diet, the walnut diet improved endothelium-dependent vasodilation, reduced levels of vascular cell adhesion molecule-1, and significantly reduced total cholesterol and LDL cholesterol. The reductions of cholesterol correlated with increases of both dietary {alpha}-linolenic acid and LDL {gamma}-tocopherol content, and changes of endothelium-dependent vasodilation correlated with those of cholesterol-to-HDL ratios.

Cognitive Health

Willis et al fed aged rats a control, or a 2, 6 or 9% walnut diet for 8 weeks before motor and cognitive testing. They found that the 2% walnut diet improved performance on rod walking, while the 6% walnut diet improved performance on the medium plank walk; the higher dose of the 9% walnut diet did not improve psychomotor performance and on the large plank actually impaired performance. All of the walnut diets improved working memory in the Morris water maze, although the 9% diet showed impaired reference memory. Thus the effect appeared dose-dependent, with no benefit and possible detriment for consuming walnuts as more than 6% of diet. So it appears that moderate intake of walnuts can improve cognitive and motor performance in aged rats.  If you have an aged rat, make sure to give him/her some walnuts!