Monday, December 20, 2010

Nuts by numbers: Should you eat them, and how much?

Nuts are generally seen as good sources of protein and magnesium. The latter plays a number of roles in the human body, and is considered critical for bone health. Nuts are also believed to be good sources of vitamin E. While there is a lot of debate about vitamin E’s role in health, it is considered by many to be a powerful antioxidant. Other than in nuts, vitamin E is not easily found in foods other than seeds and seed oils.

Some of the foods that we call nuts are actually seeds; others are legumes. For simplification, in this post I am calling nuts those foods that are generally protected by shells (some harder than others). This protective layer is what makes most people call them nuts.

Let us see how different nuts stack up against each other in terms of key nutrients. The quantities listed below are per 1 oz (28 g), and are based on data from Nutritiondata.com. All are raw. Roasting tends to reduce the vitamin content of nuts, often by half, and has little effect on the mineral content. Protein and fat content are also reduced, but not as much as the vitamin content.

These two figures show the protein, fat, and carbohydrate content of nuts (on the left); and the omega-6 and omega-3 fat content (on the right).


When we talk about nuts, walnuts are frequently presented in a very positive light. The reason normally given is that walnuts have a high omega-3 content; the plant form of omega-3, alpha-linolenic acid (ALA). That is true. But look at the large amount of omega-6 in walnuts. The difference between the omega-6 and omega-3 content in walnuts is about 8 g! And this is in only 1 oz of walnuts. That is 8 g of possibly pro-inflammatory omega-6 fats to be “neutralized”. It would take many fish oil softgels to achieve that.

Walnuts should be eaten in moderation. Most studies looking at the health effects of nuts, including walnuts, show positive results in short-term interventions. But they usually involve moderate consumption, often of 1 oz per day. Eat several ounces of walnuts every day, and you are entering industrial see oil territory in terms of omega-6 fats consumption. Maybe other nutrients in walnuts have protective effects, but still, this looks like dangerous territory; “diseases of civilization” territory.

A side note. Focusing too much on the omega-6 to omega-3 ratio of individual foods can be quite misleading. The reason is that a food with a very small amount of omega-6 (e.g., 50 mg) but close to zero omega-3 will have a very high ratio. (Any number divided by zero yields infinity.) Yet, that food will contribute little omega-6 to a person’s diet. It is the ratio at the end of the day that matters, when all foods that have been eaten are considered.

The figures below show the magnesium content of nuts (on the left); and the vitamin E content (on the right).


Let us say that you are looking for the best combination of protein, magnesium, and vitamin E. And you also want to limit your intake of omega-6 fats, which is a very wise thing to do. Then what is the best choice? It looks like it is almonds. And even they should be eaten in small amounts, as 1 oz has more than 3 g of omega-6 fats.

Macadamia nuts don’t have much omega-6; their fats are mostly monounsaturated, which are very good. Their protein to fat ratio is very low, and they don’t have much magnesium or vitamin E. Coconuts (i.e., their meat) have mostly medium-chain saturated fats, which are also very good. Coconuts have little protein, magnesium, and vitamin E. If you want to increase your intake of healthy fats, both macadamia nuts and coconuts are good choices, with macadamia nuts providing about 3 times more fat.

There are many other dietary sources of magnesium around. In fact, magnesium is found in many foods. Examples are, in approximate descending order of content: salmon, spinach, sardine, cod, halibut, banana, white potato, sweet potato, beef, chicken, pork, liver, and cabbage. This is by no means a comprehensive list.

As for vitamin E, it likes to hide in seeds. While it may be a powerful antioxidant, I wonder whether Mother Nature really had it “in mind” as she tinkered with our DNA for the last few million years.

35 comments:

Aaron Blaisdell said...

Nice breakdown of the pros and cons of nut consumption. I tend to eat macadamia nuts, pecans, and almonds on a regular basis but I have to watch it 'cause it's easy to go overboard. I recently bought a bag of raw, unshelled brazil nuts and they are delicious and loaded with selenium. I eat about 2-3 in a sitting. It's kind of fun to crack those big suckers open and dig out the meat. Chimps in the Ivory Coast use a hammer and anvil stone tool combo to crack open nuts from oil-palm trees. Must be loaded with saturated fats. No wonder these chimps are so much calmer than the ones Jane Goodall studied at Gombe.

Misty said...

I like to recommend my clients use nuts more like condiments.

It's our constant need for snacking that brings the nut to over consumption.

Like you Aaron, I eat about 3 brazils a day.

Dana Seilhan said...

Snacking isn't the only issue here; Paleo eaters and low-carbers using almonds as a flour substitute would do well to pay heed to your data.

Good for a sometime treat, but as with wheat-based baked goods, not a good idea to adopt as a staple.

David Isaak said...

"Focusing too much on the omega-6 to omega-3 ratio of individual foods can be quite misleading."

No kidding. Ratios rank a close second after percentages in terms of how they can be used to misinform.

On the topic of magnesium, some scientists have suggested that the biggest variation in intake tends to be via water, not food. People who live in areas with 'hard' water that is high in magnesium tend to have much higher intakes.

bee said...

wonder how oxidation affects all that almond flour used for baking in paleo cakes/cookies, etc.

gallier2 said...

Aaron Blaisdell

kudos to those chimps who manage to open these African nuts. My wife brought some of these last time she went home to Gabon and I have to say that they are the toughest nuts I've ever seen. The brazil nuts are peanuts in comparison. In fact they are plain and the crust is something like 4 mm thick, so there is no room for the deformation needed to crack them. We had to whack them with a hammer as they even resisted to my big pipe wrench.
From the taste they were between brazil nuts and coconuts.

Ned Kock said...

It is interesting that you mentioned those chimps being calmer Aaron. I have an article (printed version, which I cannot find right now) that argues that ancestral men developed a preference for foods rich in omega-6 in order to become more aggressive and hunt more effectively. The article also argues that ancestral men concurrently developed a bit of an aversion to those foods rich in omega-3. I must say that this theory is intriguing and worth considering, even though testosterone is a confounder.

I am not sure about hunting, but I can see extra aggression enhancing reproductive success through intra-sexual competition in the Paleolithic, while at the same time reducing survival success a bit. I say a bit because industrial seed oils were not available then.

If a trait enhances mating success enough to offset a loss in survival success its genes will spread. The situation is similar to that of the male peacock’s train.

Still, if this happened, it must have occurred in some isolated populations and not in others.

Ned Kock said...

Apparently Nutritiondata.com does not have data on Brazil nuts; the text below is from Wikipedia:

“Brazil nuts are 18% protein, 13% carbohydrates, and 69% fat. The fat breakdown is roughly 25% saturated, 41% monounsaturated, and 34% polyunsaturated.[13] The saturated fat content of Brazil nuts is among the highest of all nuts, surpassing macadamia nuts, which are primarily monounsaturated fat, and the nuts are pressed for their oil. Because of the resulting rich taste, Brazil nuts can often substitute for macadamia nuts or even coconut in recipes. Also due to their high polyunsaturated fat content, primarily omega-6, shelled Brazil nuts soon become rancid.”

“Nutritionally, Brazil nuts are a good source of some vitamins and minerals. A cup or 133 grams of Brazil nuts contains the vitamins thiamin (0.8mg -- 55% DV) and vitamin E (7.6mg -- 38% DV); minerals calcium (213mg -- 21% DV), magnesium (500mg -- 125% DV), phosphorus (946mg -- 96% DV), copper (2.3mg -- 116% DV), and manganese (1.6mg -- 81%) [15], and are perhaps the richest dietary source of selenium; one ounce can contain as much as 10 times the adult USRDA.”

“Brazil nuts have one of the highest concentrations of phytic acid at 2 to 6% of dry weight. (Phytic acid can prevent absorption of some nutrients, mainly iron, but is also a subject of research and possibly offers numerous health benefits - see phytic acid article for more information.)”

Ned Kock said...

Good point Dana. Sometimes I see low-carbers reporting anxiety and I wonder if that is not at least in part due to excess omega-6 from nuts.

Ned Kock said...

Hi David. Yes, I also heard that. Something worth looking at further.

Ned Kock said...

Very good point bee. It looks like this article has some relevant data, even if only indirectly addressing your point:

http://www.ajcn.org/content/88/4/922.abstract

anonymoose said...

Couple of Points:

1)
Missing from the comparison is Selenium! Brazil nuts are the best for this.. although it can make your hair fall out in high doses.

2)
Also, I don't think boiling/roasting is necessarily a bad thing.. its necessary, for example, to remove the dangerous tannic acid in the skin of the no-fat chestnut. Boiling and roasting also increases the resveratrol content of peanuts (as compared to eating raw).

3)
Is there any characteristics that ground nuts (like peanuts) share? I understand ground nuts are more legume than they are true tree nuts, but what does that mean?

4)
Which "nuts" are actually seeds?

5)
Speaking of seeds, what are your thoughts on chia vs. flaxseed? I've heard estrogen concerns with flaxseed, but both have good amounts of ala omega 3s and insoluble and soluble fiber, no?

LeonRover said...

When I go on mountain hikes, I take water, cashews, cheese and apples.

Anonymous said...

one thing to be wary of is the sad ability of nuts to give one kidney stones, especially almonds - which I learned on my own quite painful experience

Walter said...

Couldn't resist the urge to comment this time. I wonder too about vitamin E. If you are low carb/paleo then there is plenty of saturated fat in your diet to be used for cell wall construction/repair.

Since free-radicals cannot damage saturated fat, might that not lead to less need for antioxidants/vitamin E?

Ned Kock said...

Hi anonymoose. Almonds, pecans, and walnuts are the edible seeds of drupe fruits. The Brazil nut and cashews are also seeds. The Macadamia nut is a creamy kernel (like the palm kernel). The peanut is actually a legume.

Both the chia and the flaxseed are rich in the plant form of omega-3, ALA. Supposedly they are healthy because of that, but I think humans are better adapted to absorb the animal forms of omega-3, EPA and DHA. The reason I say this is that one doesn’t usually see the same health benefits of EPA and DHA intake with ALA intake.

Ned Kock said...

Hi Anon. What do you think is the possible connection between nut consumption and kidney stones? I can’t see any.

Ned Kock said...

Hi Walter. You may be right in that, but I’m not sure. Oxidation is necessary to convert any calorie-carrying nutrient into energy. Saturated fat in free fatty acids is also oxidized, through beta oxidation.

The reason I wonder whether vitamin E is really as important as some argue is that there are a number of other substances which are also powerful anti-oxidants. If they all play the same main role, by reacting with free radicals and becoming themselves oxidized (thus neutralizing the free radicals), then they should be generally interchangeable.

When a vitamin plays a number of other roles that clearly go beyond acting as an anti-oxidant, then it is different story. I would place vitamin D in that category.

CarbSane said...

Great post!

Regarding the walnuts, I do wonder about the paradox of walnut consumption being associated with reduced CVD risk.

Lots of low carbers who shun grains and seed oils (O6) are oblivious about the phytic acid and omega 6 contents, etc.

I try to stay clear of too many nuts. The calories just add up too fast. Lately I snack on either fresh coconut or a bite of coconut shreds.

As regards: "Focusing too much on the omega-6 to omega-3 ratio of individual foods can be quite misleading." Tis true. Especially for foods that aren't major sources of these fats to begin with (beef comes immediately to mind). But as certain nuts are major sources, it seems if one is worried about their overall balance, those nuts should be limited. Unless one is supplementing or eating flaxmeal or a ton of O3 rich fish, they're not likely to get balanced out by the other PUFA sources in your diet.

Ned Kock said...
This comment has been removed by the author.
Ned Kock said...

Hi CarbSane.

That paradox you mentioned is indeed supported by a vast amount of empirical research. But most of it is based on short-term studies where walnuts are consumed in moderation, and often in the context of low fat diets.

Add a bit more walnuts and you start seeing some signs of problems. For example, Ma et al. report on a recent study with diabetics (link below); it wasn’t in the context of a low fat diet, as the participants were allowed to eat what they wanted.

http://care.diabetesjournals.org/content/33/2/227.full

They gave the walnut group 56 g of walnuts per day. The result: “The walnut-enriched diet increased fasting serum glucose and lowered serum total cholesterol and LDL cholesterol from baseline.”

The authors present this as a positive outcome. To me it doesn’t look good at all, as fasting glucose increased by 10 mg/dl. The TC and LDL-C changes are close irrelevant in this context, in my view. They say that the fasting glucose increase was not significant but it was (at P < 0.05), and would have been more significant if there wasn’t so much variation among the participants (SD = 20.5 mg/dl).

Peter said...

What about pistachios?

Ned Kock said...

Hi Peter. Pistachios are close to almonds in terms of protein and fat content, as you can see from the first two graphs. In terms of magnesium and vitamin E content they are far behind almonds.

Ned Kock said...

By the way, nuts are not very good sources of protein. A fatty piece of steak will have more protein, and a better protein to fat ratio, than almost any equivalent amount of nuts. And the fat composition of the steak will be usually healthier.

anonymoose said...

Hi,

Gram for gram, peanuts/almonds has nearly the same amount of protein that meat has (25g of protein per 100g)!

http://www.weightlossforall.com/protein-nuts.htm

http://www.iloveindia.com/nutrition/protein/food-high-in-protein.html

Although I suppose 100g of nuts is an unlikely portion size.

http://afrsweb.usda.gov/Research/docs.htm?docid=16814

Ned Kock said...

The problem are what is referred to as the "quality" of the protein, and the fat content. Let us take peanuts, for example, which have the highest protein content of all of the nuts discussed in the post. Roasting reduces the protein content a bit. But even without roasting, the amino-acid score (a measure of actual usable protein content) of peanuts is 25 percent lower than that of beef.

As for the fat content, 100 g of peanuts will contain 50 g of fat (more than twice as much protein), 15 g of which will be omega-6.

Jack C said...

Ned,

In your comment on Brazil nuts (December 20) you discussed their high phytate content and noted that while phytates bind to minerals such as magnesium, they also have benefits "as discussed in the article on phytates"

I have been unable to locate the "article on phytates" you mentioned on your blog. Please advise.

The studies on tooth decay by Dr. Mellanby 80 years ago suggest that phyates in cereal grains are a cause of tooth decay.

Phytates can be greatly reduced in nuts by soaking and low temperature drying, but that is a lot of work. You can buy nuts that have been soaked and dried, but they are quite expensive (but also very good).

What are your thoughts on the importance of reducing phytates in nuts by soaking and drying?

Ned Kock said...

Hi Jack. That text on Brazil nuts was taken verbatim from Wikipedia, so that article that is referred there at the end of the text is a Wikipedia article.

It seems that phytate content is high enough in most nuts to be at least of a bit of concern among some researchers; one notable exception is the coconut:

http://www.ajcn.org/content/47/2/270.abstract

Drying and roasting seems to work, although some say that roasting increases AGE formation in nuts. (I am generally skeptical of claims about exogenous AGEs causing major health problems.) Soaking should work, as it does with legumes and grains:

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=909168

Having said that, there are some researches who believe, based on reasonable empirical evidence, that phytates can also be health-promoting:

http://linkinghub.elsevier.com/retrieve/pii/027153179500040P

Anonymous said...

Hi Ned,

Try brazilnuts instead of brazil nuts in NutritionData.

Ned Kock said...

Hi Anon, thanks.

Walter said...

Am I reading your graph right? Almondso omega are all omega 6 and no omega 3?

Ned Kock said...

Hi Walter. Yes, almonds have practically no O3, like most nuts.

Avishek said...

This confuses me: i would think the ratio does have a significance. Are you assuming that ALA does not matter?

THere are "spots" for omega-6 and 3 in the brain, so if one consumes only nuts containing omega-6, they worsen their ratio in the brain. Now ala does not convert to DHA, but it can convert to EPA, and keep DHA status the same.

We'd also have to consider the total amount of calories consumed. I'm more likely to binge on peanut butter than walnuts.
I was thinking of leptin and omega-3 and came across this study in rats that sort of talks about the ratio and altered fatty acid composition in the milk.
http://www.jlr.org/content/43/10/1743.long


This was quite interesting, and they did not elaborate: "The content of 22:6(n-3) was reduced in the n-3 group compared with the n-6/n-3 group." That's DHA. Hmm... and they used soy bean oil. I'm going to read some more studies on walnuts like the one you posted to get this straight.

Anonymous said...

"Any number divided by zero yields infinity."

Ned!!

George Henderson said...

Vitamin E is a vitamin (essential for some as-yet unknown reaction or hormonal effect) not just an antioxidant. High-SFA diets reduce the antioxidant need for Vit E.
The only function of vit E that's known it to stabilize the conversion of carotenoids to retinol, and it's uncertain if this is unique to Vit E.
Science does not in fact know everything yet. We need to keep open minds about E, but the amount in animal fats seems to prevent deficiency.