Friday, March 5, 2010

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!


Anand Srivastava said...

Hi Don excellent post.

I went searching for magnesium content of walnut, cashews and almonds. I find that both cashews and almonds have quite a bit more magnesium than walnut.

I couldn't determine what extra minerals are in walnuts compared to cashews and almonds. Both have a lower omega6 content than walnuts. Cashews are also much lower in energy, so that you can easily eat more. Giving a higher density of magnesium and other minerals.

Anand Srivastava said...

Are you thinking of doing a post on Fermentation and its relation to health?

These days I am realizing that the fridge might be a big reason for our ill health ;-).

I am trying to add more fermented foods like kefir into my diet.

PaleoDoc MD, PhD said...

I have a weakness for nuts, and sometimes succumb to a small jar of hazelnut butter. Hazelnuts spread in Europe during the Paleolithic following human migration. But still, it I have issues with them:

1. You may not not worry about omega-6 in mongongo is you are getting plenty of omega-3 from animal meat and organs.

2. Nuts need to be roasted (soaked/sprouted?) to get rid of the phytic acid. !Kung rosted them. If I eat nuts after meat, some of the meat does not get digested, causing indigestion and gas. Nut by themselves as a late night snack appear to be ok.

3. Roasted nuts are full of AGEs, acrolein, other produts of pyrolysis. Maybe !Kung handled that well by cooking less in general. Besides, nuts are seasonal too, March-May for mongongo. I suppose !Kung did not manage to get year's supply, plus they moved around a lot.

3. Nuts contain a lot of phytoestrogenic chemicals. They are touted as beneficial for male health (mostly hair loss), but they decrease DHT with all its consequences. Same issue with olive oil. Perhaps women ate most of the mongongos, while male hunters had wildbeests' hearts?

4. Nuts are acidic, possibly hazelnuts the least so. Not a problem if you eat lots of greens and little meat/fish.

5. Fresh nuts are hard to get. Rancid nuts are poison.

But fresh juicy walnuts in season are hard to beat!

epistemocrat said...

Hi Don,

I too enjoy my nuts, and I think this is an important general concept to always keep in mind:

"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."

Many of these compounds and their effects are currently 'unseen' by humans and science, but ancestral wisdom has still found ways to respond to the invisible to protect and achieve health. We always must factor for the unseen in science philosophy; we also have to analyze things in context.



Melissa said...

I have often wondered about the omega-6 in nuts. Omega-6 in oils have negative effects, but nuts have been shown to have positive effects in many many studies. I wonder if it's because oils are more likely to be heavily oxidized.

Anonymous said...

I've been a big fan of of the almond, but like all things - I was snacking on them just a bit too much. I've added walnuts to salads here and there, but this reinforces my quest for more walnuts, less almonds. Good info!

Chris D said...


Hard to frame the impact of the mongongo nut on the !Kung.

If they ate 4% or more of their calories as w-3, it would be enough to offset the 10 or so percent w-6 provided from the nuts according to this chart from Lands on whole health source.

As w-6 seems to "activate" the immune system, it may confer some health benefit to hunter gathers living in environments with relatively more endemic disease.

The cost/benefit of added w-6 to a western diet may not be worth the offset to longevity from "disease of civilization" given the status of public health.

kilton9 said...

How sure are we about the Kung! and mongongo nuts? Information seems conflicting, perhaps depending on when a given anthropologist visited the area.

I'm aware of support for high consumption in the book Nisa, for which data was collected in 1970-1971. The mongongo nut is called the staple food, and "constitutes more than half of the vegetable diet".

However, an earlier account from The Old Way -- based on the author's several visits to the Kalahari spanning several years in the 1950s -- tells a different story. A few quotes:

"The meat of big game, large harvests of nuts...were profoundly welcomed by all concerned, but months could pass before the people obtained these kinds of foods. Most of the time, people at the berries, roots, and slow game obtained by ordinary, everyday gathering."

"By far the most important staple foods of the Ju/wasi were roots-- the twenty-five kinds of bulbs, rhizomes, corms, and tubers."

Anyone have additional data?

Don said...


Of course nuts were seasonal. The info in The Old Way does not contradict the finding that mongongo provided !Kung a large portion of their calories:

"Like many trees of seasonally arid or cold climates, the trees lose their leaves every year, towards the end of the cold-dry season of autumn and winter (variably, about June to the end of August). And it is at this time that the last of the ripe fruit fall. They are a lot easier to see when the leaves fall at this time, and it is easy to pick up the fallen fruit. The supply of fruit decreases after winter, as the rainy season (very variably, at some time in the period November to April, broadly regarded as the 'summer rainfall' area) comes on; insect and animals destroy the fruit where they fall. Even the dried, crumbly flesh of old fruit is edible -there may be edible dried fruit on the ground for as long as eight months, overlapping the fall of the new crop. Some bushmen remove the flesh from the fresh fruit, dry it in the sun, and store it for use later in the year. Both Bantu and Bushman peoples use the fruits, with the modern preference being to boil the whole fruit to remove the tough and indigestible outer skin, and make a sweet, maroon colored porridge - very similar to'applesauce'(USA)/stewed apples (British colonial) - from the flesh."

Thus the !Kung had access to some mongongo nut/fruit at least 8 months of the year and even that overlapped the new crop, and they dried some for use out of season.

kilton9 said...


Thanks. It's more the "up to 50% of their calories" statement that I was referring to. I wasn't attempting to suggest that nuts weren't a significant part of their diet.

Don said...


Regarding the role of nuts in the !Kung diet, mongongos, by virtue of their relatively high caloric density, could have both provided 1/3 of calories (as estimated by Richard Lee) and appeared to Elizabeth Marshall Thomas be a relatively small part of a diet dominated by roots and tubers.

To illustrate, one cup of walnuts provides about 650 calories, about 1/3 of 2000. If I made sweet potatoes the only other food in this diet, I would have to eat about 1300g, or 13 medium sweet potatoes – about 13 cups mashed – to get the other 1350 calories. If I used carrots alone, I would need more like 26 cooked cups. Visually, it would appear to someone unaware of caloric density that sweet potatoes far outweighed walnuts in importance as staple foods – 13 cups of sweet potatoes vs. 1 cup of walnuts. Yet the walnuts would be providing 1/3 of the calories.

Carrots have only 43 kcal/100g, sweet potato only 103 kcal/100g, and walnuts 618 kcal/100g. In short, the nuts have at least 6-15 times the caloric density of roots and tubers, so a relatively small, seemingly insignificant volume of nuts (compared to the volume of roots and tubers consumed) could make relatively large (30-50%) contributions to the energy intake of the !Kung. People unaware of the caloric density of foods will thus underestimate the importance of some foods in a diet, and it seems likely that Elizabeth Thomas exemplified this in her evaluation of the !Kung diet.

Don said...


1. I get plenty of n-3 from grass fed meat and salmon, sardines, and fish oil.

2. I often eat 1/2 cup of raw walnuts after eating 10-12 ounces of meat. I don't notice any gas or maldigestion of protein. From experience I think the ill effects of phytates are less than suggested by some authors. I also have seen research indicating that people adapt to phytates to a certain extent. Don't have the paper handy but I think you can find it on PubMed.

3. I think the dangers of cooking are also overstated. We have a liver that can detoxify these things if properly nourished. !Kung had mongongo for more than a few months. If concerned you can soak, sprout, and dry. I used to roast all my nuts, but found I can eat most of them raw with no ill effects; in fact, now it seems that roasted nuts feel more difficult to digest at times.

4. That's just silly. !Kung men ate mongongos also (well documented). In fact, as Jared Diamond quoted in his article The Greatest Mistake in the History of the Human Race (agriculture), one !Kung man was asked why he did not practice agriculture, in response he laughed and said "Why should I work that hard when the world provides so many mongongo nuts?"

Good to reduce DHT, it plays a role in acne, baldness, and prostate cancer. Maybe you meant that they decrease testosterone? If so, do you have a reference, a clinical trial demonstrating that eating walnuts causes men to have abnormally low testosterone? I have not seen one.

In Chinese medicine, we use walnuts actually to fortify the yang (male function). This could result from phytosterols reducing the wasteful conversion of testosterone to DHT.

5. I already provide an example of a 2000 kcal diet containing about 100g walnuts per day and nearly 12 ounces of meat that was net alkaline residue.

I don't consider 12 oz of meat "little" meat, since it provides 84+g protein, more than 50% more than the RDA for a 154lb/70kg male.

6. I have no problem getting fresh tasting nuts. Nuts contain many antioxidants that protect the oils. Nature makes them that way; the seed has to preserve the oils for at least some months until it can sprout and the sprout will need fresh oils when it starts growing.

Don said...


I think you are right, once oils are removed from their seeds which contain many natural antioxidants, they are very prone to oxidation. Oils are processed foods, whole nuts are not.

Chris D said...


You never responded to Stephan's reply to your comment on this blog post.

"As far as the !Kung however... they do eat a ton of LA-rich mongongo nuts, but they're also possibly the least healthy HG tribe I know of. Body composition is often poor (undermuscled) and I believe they have a measurable incidence of heart attack."

If this is the case, and the !Kung are the least healthy of a body of populations whose health we're looking to emulate, are they a good model for the safty of large nut intake?

Flowerdew Onehundred said...

I don't consider 12 oz of meat "little" meat, since it provides 84+g protein, more than 50% more than the RDA for a 154lb/70kg male.

You mean 150%, right? The RDA for protein for men and women is very low (46g/56g). If I eat that little protein, I have problems with hunger that fat cannot fix.

Don said...

Chris D,

Too many things to do, can't keep up with every blog I comment on. If you go there now you will see that I responded. I will here also.

First, H-Gs are just my guide...If they eat nuts, then I also look at current research and test it myself and find if it works for me. If it does, then I expect it will work for others.

I eat walnuts, often 1/2 cup or more daily. At 5'9" and about 155 lbs, not more than 10% fat, capable of sets of chins with added 25 lbs and bench pressing 173 lbs for 3 sets of 5, I am not undermuscled or overfat compared to a typical H-G or the average US citizen.

Further, I just showed that the research on walnuts pretty clearly indicates that they help prevent, not cause, cardiovascular disease. Even if !Kung did have heart disease (they don’t), it would not be because they eat mongongos.

It seems that the book “Other ways of growing old: anthropological perspectives”
by Pamela Amoss and Stevan Harrell (link below, p. 83) disputes Stephan’s claim that !Kung have a measurable rate of CHD. It reports that !Kung have no hypertension or signs of CHD at any age.

It does mention cataracts as a common problem among the !Kung, but I would find it difficult to sort out the effect of diet from the effect of spending one's entire life exposed to the blinding sunlight of the desert (which would stress the lense).

In the same book (p.82), the author reports that Howell entered a !Kung camp one day to find 4 females playing jump rope. Their ages were 8, 11. 15, and 66. The older woman "was at least as active and enthusiastic as the children." This casts doubt on the "undermuscled" comment also.

How do you define "undermuscled"? If you mean that contemporary !Kung don't look like modern athletes or the people on the covers of Men's Health or Oxygen I would agree.

However I would call a person "undermuscled" only if s/he did not have enough functional musculature to carry out required activities and play. Since !Kung not only succeed at hunting and gathering but also engage in vigorous play even at advanced ages I’d say they have plenty of muscle.

Further, degree of muscularity is primarily determined by intensity of activity and exertion against resistance, only secondarily by protein content of diet. So if !Kung have less muscle than, say Plains bison hunters, it would be primarily because they engage in less high intensity activity, not because they eat mongongos.

For example, !Kung hunt primarily medium size game like wildebeest and Kuru. Lifting these does not require as much muscle as team lifting small herds of 1500-2000 lb. bison out of ravines the way Plains Indians did. If Plains Indians had more muscle it was because they lifted heavier things, not because they ate more bison and less nuts. (BTW Plains bison hunters also ate pine nuts.)

As for protein, it may be that contemporary !Kung have a less than optimum intake of animal protein, but that is not the fault of eating mongongos. That is a result of being confined to the Khalahari. Archaeological evidence indicates that prehistoric people did not hang out in deserts.

I don’t maintain that every aspect of the contemporary !Kung diet is ideal. It probably has too little n-3, iodide, and other nutrients best provided by marine and lacustrine ecosystems exploited by prehistoric ancestors. So I use the general outline of their diet as a model, but keep in mind modern research and their diplacement from the optimum ecosystem.

If you want to see what !Kung look like for yourself, watch the film Journey of Man online. Despite some modern influence, they appear lean and no less muscular than say Australian Aborigines, who also eat lots of nuts.

Don said...


Right. I said "more than 50% more than", an awkward way of saying "more than 150% of the RDA.

PaleoDoc MD, PhD said...

Re DHT, as far as I understand it, polyphenols, lignans etc in nuts, sesame seeds, olive oil and other plant foods inhibit conversion of testosterone to DHT. This necessarily increases plasma testosterone level. We need testosterone pretty much only for muscles, which is important, but it is DHT what makes men good hunters or warriors. DHT determines mental function, libido, facial and body hair and external features. True, nut can help you stop losing hair, but lower DHT has consequences. Plus, I think that there are other factors in hair loss, possibly fatty acids and inflammation, so lower DHT may not be necessary.

Don said...


I also agree with you, the RDA for protein is too low to give optimum health and appetite control. I think that the optimum lies somewhere between 1.5 to 3.0 times the RDA. In that I include protein from both meat and plants. My diet provides nearly 3x the RDA for my weight: ~150g per day (+/-25g) compared to 56g/d RDA.

Chris D said...


I've always had trouble stuffing more than 100g of protein down my throat a day. I just loose a taste for flesh after a point, have any pointers?

I'll also note that i've used 3-10 grams of BCAA's pre workout for a few years now, and that I tend to consume 10-30% carbs.


Dietary saturated fat is also correlated with plasma testosterone concentrations, Kraemer has investigated this a bit.

How do you think this plays into the nuts/polyphenols/testosterone/dht interplay?

Don said...


I think that DHT is just like everything else, too little is bad, too much is bad, in between we find an optimum. I haven't heard of anyone losing their masculinity by eating nuts. I think that since our metabolisms evolved in an environment and probably on a diet that included alpha-5 reductase inhibitors, we may have a-5-r expression that is adapted to presence of inhibitors, and thus may require an intake of them (phytosterols, polyphenols, etc.) to prevent over expression of alpha-5 reductase leading to acne, prostate hypertrophy, hair loss, etc. This would explain why we express disorders associated with DHT in civilized groups, but not among !Kung, Aborigines, etc.

I have always been amazed at the photos Price took of aged Australian Aborigine men (p. 167 of hardback edition of NPD) showing them with virtually full heads of hair, like traditional Chinese or Japanese men. As I have noted, Aborigines also ate many kinds of nuts.

Which brings me to the warrior comment. I can't think of any more warrior-like men than the Samurai, or Japanese when they invaded China, or Japanese Kamikaze pilots, coming from men eating plenty of alpha-5 reductase inhibitors (sesame, soy, nuts, rice, beans). I just don't buy the idea that eating plants produces abnormally low DHT. Certainly not the case in Okinawa.

Don said...

Chris D,

1) The point at which you lose your taste for meat is the point you should stop eating it. I consider it your body regulating your intake to your needs. I experience the same thing on many days. Often on days I train hard, I want more animal protein, then within 36 hours I have a reduced desire for meat until I train again.

2) I hover around 15-20% carbs, similar to you. Eating adequate carbohydrate reduces protein requirements. That's a good thing in my book. Why spend $ on protein only to convert it to sugar? Just eat the carbs instead (fruits, vegetables, some tubers and roots) and save your kidneys the wear and tear and control your expenses. I average 125-150 g CHO daily. You're going to burn ~150 g glucose daily seems rational to me to eat that directly rather than waste protein.

3) I don't think anyone eating a paleo diet with some nuts needs to worry about testosterone or DHT. I eat plenty of nuts, still expressing characteristics associated with DHT (e.g. gradual male pattern baldness) though less so than found in previous generation of my family.

lightcan said...

Hi Don,

talking about nuts and magnesium content. My daughter is almost 7 and sometimes complains of muscle cramps. I was thinking that it might be Mg and tried to give her almonds and pumpkin seeds. Is it worth soaking them in Evian with vinegar to help reduce phytic acid to make sure she's getting the magnesium? or just give them raw as they are on their own as a snack?

Don said...


I think it is worthwhile to soak if you have the time, and probably more efficient just to give her a magnesium supplement. In paleo times, people likely got significant mineral nutrition from water they drank. Not everyone today has water with significant magnesium contents. Supplements fill this gap.

lightcan said...

Thank you, Don, I do have the time, I just prepare them in advance, soak, dry in low oven. I suppose the energy needed to dry them might be a disadvantage.

ValerieAnne said...

I soak and dry walnuts, almonds and pecans according to the Nourishing Traditions cookbook. It is supposed to make them more nutritious and digestable. I haven't noticed a difference other than taste. Walnuts and pecans are particularly more buttery and less bitter tasting. I once went on a 6-week Chinese medicine cleansing diet. The breakfast consisted of 10 walnut halves and red-colored fruit. I was very surprised to find out how satisfying 10 walnut halves can be.

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surfa01234 said...

Wow, amazing thoughts Don, love your work! It seems there are conflicting thoughts on nuts and phytic acid. Do we have hard data on the best way to reduce it? i.e. what to soak in, how long for, what temperature, should we crush the nut first, should it be raw or roasted before soaking, is roasted enough...

what are your thoughts on this:


Don said...


1) Consuming foods rich in ascorbate (vitamin C) with foods rich in phytate can cancel the negative effects of phytate on mineral absorption.

2) Some studies show humans who have diets high in phytate upregulate phytase and have substantial degradation of phytate in the gut:

3) Phytates appear to have anticancer effects by binding excess minerals.

In short, I don't think we should be trying to get all of the phytates out of our foods. So far as I can tell, phytate caused nutritional deficiencies only in people who have limited diets low in vegetables, fruits, and total mineral contents, e.g. people trying to live entirely on unleavened bread and legumes.

surfa01234 said...

Good points. I can't seem to digest nuts, they come out looking chewed but not digested. (like corn)