Tuesday, February 24, 2009

A few thoughts on Minerals, Milling, Grains and Tubers

One of the things I've been noticing in my readings on grain processing and mineral bioavailability is that it's difficult to make whole grains into a good source of minerals. Whole grains naturally contain more minerals that milled grains where the bran and germ are removed, but most of the minerals are bound up in ways that prevent their absorption.

The phytic acid content of whole grains is the main reason for their low mineral bioavailability. Brown rice, simply cooked, provides very little iron and essentially no zinc due to its high concentration of phytic acid. Milling brown rice, which turns it into white rice, removes most of the minerals but also most of the phytic acid, leaving mineral bioavailability similar to or perhaps even better than brown rice (the ratio of phytic acid to iron and zinc actually decreases after milling rice). If you're going to throw rice into the rice cooker without preparing it first, white rice may actually deliver an overall higher level of certain minerals than brown rice, though brown rice may have other advantages such as a higher feeling of fullness per calorie. Either way, the mineral availability of rice is low. Here's how Dr. Robert Hamer's group put it when they evaluated the mineral content of 56 varieties of Chinese rice:
This study shows that the mineral bio-availability of Chinese rice varieties will be [less than] 4%. Despite the variation in mineral contents, in all cases the [phytic acid] present is expected to render most mineral present unavailable. We conclude that there is scope for optimisation of mineral contents of rice by matching suitable varieties and growing regions, and that rice products require processing that retains minerals but results in thorough dephytinisation.
It's important to note that milling removes most of the vitamin content of the brown rice, and most of the fiber, both of which could be disadvantageous depending on what your overall diet looks like.

Potatoes and other tubers contain much less phytic acid than whole grains, which may be one reason why they're a common feature of extremely healthy cultures such as the Kitavans. I went on NutritionData to see if potatoes have a better mineral-to-phytic acid ratio than grains. They do have a better ratio than whole grains, although whole grains contain more total minerals.

Soaking grains reduces their phytic acid content, but the extent depends on the grain. Gluten grain flours digest their own phytic acid very quickly when soaked, due to the presence of the enzyme phytase. Because of this, bread is fairly low in phytic acid, although whole grain yeast breads contain more than sourdough breads. Buckwheat flour also has a high phytase activity. The more intact the grain, the slower it breaks down its own phytic acid upon soaking. Some grains, like rice, don't have much phytase activity so they degrade phytic acid slowly. Other grains, like oats and kasha, are toasted before you buy them, which kills the phytase.

Whole grains generally contain so much phytic acid that modest reductions don't free up much of the mineral content for absorption. Many of the studies I've read, including this one, show that soaking brown rice doesn't really free up its zinc or iron content. But I like brown rice, so I want to find a way to prepare it well. It's actually quite rich in vitamins and minerals if you can absorb them.

One of the things many of these studies overlook is the effect of pH on phytic acid degradation. Grain phytase is maximally active around pH 4.5-5.5. That's slightly acidic. Most of the studies I've read soaked rice in water with a neutral pH, including the one above. Adding a tablespoon of whey, yogurt, vinegar or lemon juice per cup of grains to your soaking medium will lower the pH and increase phytase activity. Temperature is also an important factor, with approximately 50 C (122 F) being the optimum. I like to put my soaking grains and beans on the heating vent in my kitchen.

I don't know exactly how much adding acid and soaking at a warm temperature will increase the mineral availability of brown rice (if at all), because I haven't found it in the literature. The bacteria present if you soak it in whey, unfiltered vinegar or yogurt could potentially aid the digestion of phytic acid. Another strategy is to add the flour of a high-phytase grain like buckwheat to the soaking medium. This works for soaking flours, perhaps it would help with whole grains as well?

So now we come to the next problem. Phytic acid is a medium-sized molecule. If you break it down and it lets go of the minerals it's chelating, the minerals are more likely to diffuse out of the grain into your soaking medium, which you then discard because it also contains the tannins, saponins and other anti-nutrients that you want to get rid of. That seems to be exactly what happens, at least in the case of brown rice.

So what's the best solution for maximal mineral and vitamin content? Do what traditional cultures have been doing for millenia: soak, grind and ferment whole grains. This eliminates nearly all the phytic acid, dramatically increasing mineral bioavailiability. Fermenting batter doesn't lose minerals because there's nowhere for them to go. In the West, we use this process to make bread. In Africa, they do it to make ogi, injera, and a number of other fermented grain dishes. In India, they grind rice and beans to make idli and dosas. In the Phillipines, they ferment ground rice to make puto. Fermenting ground whole grains is the most reliable way to improve their mineral bioavailability and nutritional value in general.

But isn't having a rice cooker full of steaming brown rice so nice? I'm still working on finding a reliable way to increase its nutritional value.


Mark said...

Hello Stephan,
So if we don't have the time to do our own soaking/milling and want to use carbs that are safe in regular form (along with veggies and fruits), are you saying that potatoes and white rice are fine as long as we don't eat too much due to the glycemic response (which is why I don't include white flour)? Also, are sweet potatoes still better than white potatoes? Lastly, sorry for all the questions, when it comes to fat loss in the typical American who is 15 to 20 pounds overweight, do you think it is necessary to go low carb (under 100g per day) for some time to allow the body lean out and regain insulin sensitivity before they introduce more carbs? Essentially, I think the Kitavin's can handle their diet of high carbs because their systems aren't messed up from growing up on a typical Western diet. Please let me know if it would be easier for me to just e-mail you. Thank you, your blog is great!

katherine said...

I have a question about the idli...you say you make them yourself, but do you use the special pans for steaming or some other method? I can't seem to find the pans/molds anywhere!

JBG said...

Stephan, your comments about white vs brown rice perhaps resolve a puzzle I've wondered about for a long time: why do the Asians, who are so thorough in extracting every bit of food value from the things they eat (eg, by eating things, and parts of things, that it would hardly occur to a Western person to eat), eat white rice rather than brown rice? You may have supplied the answer.

But your side comment about vitamins in brown rice is important too. I recall reading once that at the time of the US conquest of the Philippines, ca 1899, some do-good American ladies visiting the islands persuaded the authorities to stop feeding prison inmates brown rice (regarded by locals as "pig food") and giving them white rice instead. Since the prisoners got little besides rice, after awhile they started dying of beri-beri.

dan said...


It seems humans go to great lengths to eat grains. Do you know what types of animals subside on a diet of grains and what the difference between their digestive system and ours is?

dan said...


Follow-up question. Does brown rice have enough phytic acid to bind to and reduce your ability to absorb minerals from other parts of your meal beyond just those of the brown rice?

Nancy said...

Why would humans spend so much time and effort on making grains edible when you can get better nutrition in other ways from other vegetables and fruits?

Aaron said...

Nancy, grains keep longer than fruits or veggies. Plus, grains and tubers are a good source of non-fructose carbohydrates!

Stephen, I think it's interesting that my body seems to tolerate creamy buckwheat a lot better than the whole groat <---- maybe it's because of increased phytase activity? Do you have any literature about the best ways to soak buckwheat- or to ferment it? I wonder if crushing it after soaking is going to make it even better to consume!

Also, I use nutrition data all the time and have never seen where the phyate content is listed-- could you tell me where to find it?

Lastly, have you ever considered making a post on what you think our mineral requirements are? I would actually assume they are pretty low considering what you can get by on without major disease. I'm interested to see what you think of minerals such as magnesium- which is barely present in breast milk during a crucial growth period. --- but at the same time is suggested at 1:2 ratios with calcium-- when its more like 1:12 in breast milk-- maybe you need more magnesium if you consume more carbs.

Stephan Guyenet said...


In my opinion, white rice and potatoes are safe carbohydrates as long as you handle your glucose well. Potatoes are probably better because the vitamin C aids in mineral absorption. I'm not concerned about the glycemic index, I think it's not a very useful measure. White flour is a problem because of the gluten (and perhaps also because of chemicals like alloxan formed during bleaching), rather than the glycemic index.

I don't know whether it's necessary to go low-carb to regain insulin sensitivity, but I doubt it. The paleo diet trials argue against that. I think what most people need to do to regain insulin sensitivity is drop wheat, sugar, vegetable oil and processed food in general.

But the low-carb approach obviously works. The question is, does it work simply because it reduces flour and sugar consumption? I don't have a definitive answer, but I suspect based on a lot of indirect evidence that's the main reason it works.


You can order idli pans on line. Personally, I just bake them in muffin trays. It's not traditional but they taste good.


I agree, if your diet is mostly white rice, you need a source of micronutrients from somewhere else. White rice is a fairly empty calorie source, which has both advantages and drawbacks compared to brown rice.


Ruminants like cows eat some grass seeds in the fall. They have several stomachs and a huge digestive system overall that acts as a fermentation tank, allowing microorganisms to break the fiber down so they can absorb nutrients from it. Rodents also eat grass seeds in the wild. I don't know much about their digestive system, but I don't believe they carry any of the HLA loci that predispose to gluten sensitivity, as humans do. So you can't really study gluten toxicity very well in them.

Whole grains, and especially bran, do have the ability to prevent mineral absorption from other parts of a meal, if I've understood the research correctly. I'll be posting on this later.


Cost and convenience. Grains are very productive and they store well. If you are a well-off American, you can afford to eat paleo, but if you're a poor African or an American trying to make ends meet, grains are an attractive option.


Make sure the buckwheat you buy is raw if you want to soak it, because toasted buckwheat has no phytase activity (raw usually has a greenish tinge). Raw buckwheat has a pretty high phytase activity. Buckwheat isn't actually a grain (technically) so I don't know if soaking in acid applies to it as well. But I would guess it does, and soaking in warm water definitely applies.

Mineral requirements are a can of worms I haven't opened yet. I'm not super motivated to parse out all the research on that, since I think the answer will boil down to: eat whole foods, prepared traditionally.

Nancy said...

Cost and convenience. Grains are very productive and they store well. If you are a well-off American, you can afford to eat paleo, but if you're a poor African or an American trying to make ends meet, grains are an attractive option.

Well, now they're cheap. And we've forced most of Africa into cities and agrarian lives from what was once probably hunter gather lives, so yeah, they can only afford grains now.

But what I'm saying is, grains aren't foods we evolved to eat and we have to process the heck out of them (fermenting, soaking, milling) before we can disable the stuff that isn't good for us.

I'm just not seeing the benefit of people who CAN afford to eat other food in spending that much time trying to defeat the bad stuff in grains. Leave grains for the birds. We can eat tubers if we feel we need starch, green veggies, squashes, cauliflower and so on and probably avoid some of the bad stuff in grains we can't process out entirely.

Or are we too addicted? Those gliadin proteins break down into peptides that resemble opioids and bind to morphine receptors in our body. This could explain why so I hear so many people say "I could never give up [bread|pasta|muffins]" when I tell them about my diet.

Carl M. said...

Regarding buckwheat: the sprouts are somewhat toxic, so don't soak buckwheat too long.

Robert Andrew Brown said...

Thanks Stephan

Another great thought provoking post.

Stephan Guyenet said...


I agree that it's not necessary to eat grains by any means, and it definitely takes work to make them healthy. But I still think there are reasons why someone would want to eat them.

There's nothing cheaper. You can buy brown rice for 20c a pound. You can get potatoes for maybe 30c a pound if you're lucky, but that's wet weight so it ends up being probably 5X more expensive per calorie.

One of the things I'm interested in is how to eat well for cheap. I'm also interested in how to explain the fact that some traditional cultures eat grains and are healthy, when they seem to be so bad for us in the U.S. All those things make me interested in learning about it, writing about it and making the information available. I definitely understand the sentiment of wanting to avoid them altogether, but I would rather not limit myself if I can avoid it.


Thanks for the tip.

Peter N said...

Hi Stephan- Sorry to ask a question you may have already addressed, but, if white flour is unhealthy because of gluten and other toxins, why do the French seem to be healthy with a large amount of it in their diet? Is it actually true that they eat a lot of white flour in France? I know they ferment it in sourdough form, but pastries also seem to be a French claim to fame. Somehow to me it seems as if white flour in France is as benign as white rice in Japan- not healthy in and of itself, but not causing widespread health problems either. Did Price see degeneration in people who were exposed to white flour without white sugar?

Stephan Guyenet said...


Very good question. I've thought about this quite a bit. First of all, the French are healthy only by the standards of industrial nations. They still suffer from plenty of chronic disease, but they do have a low heart attack death rate and obesity rate compared to other industrial nations.

Obviously wheat is a staple in France, but they don't eat an extravagant amount of it. It's not the same as rice in Asia. They have a relatively high fat intake, and a high intake of saturated fat. A lot of it comes from good quality dairy, so they have a high intake of fat-soluble vitamins. They don't eat much processed vegetable oil, although that's changing.

They also traditionally eat organs and a variety of seafood, and generally focus on good, fresh food. They eat less sugar than Americans as well.

The traditional French diet, with the exception of wheat, is very healthy overall. Health is multi-factorial, and they're doing a lot right. My opinion is that they would be healthier without the wheat and sugar.

chlOe said...

French people who are not obese probably also walk a lot, avoid gyms, eat less (quantity, maybe not quality - such as eating fat would be better then eating a tiny salad) and eat fresh food. I had read a story before of a woman who took a vacation to France with her friend and didn't think about anything she ate, they just decided to splurge or whatever, and they actually lost weight. When they returned to America they wanted to eat healthy so they started drinking soy milk, cereals, etc. and actually gained weight. Looking at the ingredients, always one of the second or third things in the list is some kind of cane sugar or sugar product. Not saying sugar caused it, but putting sugar in every single boxed or packaged product probably does some damage to our obesity rate. What it's paired with. They even put high fructose corn syrup in Robitussin...a cough medicine. Great way to cure a cold, I guess. Other then the menthol in it.
Just wanted to add that.
And I hope European countries don't completely go cheap with their food.

Stephan Guyenet said...


I've hear anecdotes like that as well. Overweight people tend to lose weight when they live in Europe, and gain it when they live here.

chlOe said...

Yep. I've also talked to one of my friend's 'uncle' who lives in Germany, and when he comes over here he puts on 15 pounds easily. He says the food has more "flavor" (which I like to call MSG and sugar) which makes him want to eat more of it.
Same with Heidi Klum, the super model from Germany.

Peter N said...

Thanks for the insights on the French, Stephan. I guess I'll aim for a Kitavan level of health rather than a French one. Root veggies with butter!

S. said...

I don't know exactly how much adding acid and soaking at a warm temperature will increase the mineral availability of brown rice (if at all), because I haven't found it in the literature.

Maybe this one? Not sure if it slipped under your radar. Effect of soaking and phytase treatment on phytic acid, calcium, iron and zinc in rice fractions

Many of the studies I've read, including this one, show that soaking brown rice doesn't really free up its zinc or iron content.

I didn't see anything about brown rice in that study - just numbers relating to rice/legume mixtures (fermentation = increased zinc and iron bioavailability). Did I miss something? Sorry if this is a silly question!

Stephan Guyenet said...


Yes, I just noticed that study because it just came out. I looked at the full text and it's not as promising as the abstract makes it sound. They soaked the brown rice in the acid buffer for something like 5 days. Even then, it only reduced PA by 75%.

The full text of the link I posted has numbers for soaking rice.

UpChuckChuck said...

Wait a minute, since when do potatoes contain similar nutritive values to either white rice or white flour? According to the nutritiondata website, potatoes contain a veritable amount of vitamins and minerals. In fact, coming short of a molybdenum deficiency, one can live exclusively on potatoes and milk products, to the exclusion of everything else.

It should come as no surprise that the humble potato has supported many cultures nutritionally for many thousands of years, so it's really "a white lie" to compare it as such.

I'll have you know that it's a mighty tuber that nourishes the greatest ratio of centenarians per 100, 000 people, the Okinawans, who eat purple sweet potato.

Starch is pathway to longevity, and potatoes are a ticket to longevity.


Stephan Guyenet said...


If you compare potatoes to refined grains on a per calorie basis, they both have a relatively low vitamin, mineral and phytic acid content overall. The major exception is vitamin C, which I agree is a point in favor of potatoes.

The Okinawans eat sweet potatoes, which are not related to potatoes.

Anonymous said...

But what about the Italians! They surely eat as much white flour produce (bread,pasta) as the asians do white rice.

Unknown said...

Hello Stephen, I don't know if you've come across this before but I thought you might find it interesting: http://www.youtube.com/watch?v=kGavEbHNTJU&feature=related

if you wait about a minute it starts talking about tubers and then continues on part 6. It's an interesting little bit on traditional processing of tubers.

JBG said...

The segment about tubers Matthew speaks of starts about two minutes into the video and lasts about two minutes. It concerns a poisonous Australian yam which aborigines render edible by first baking it, then grating it, then soaking it in running water for about a day. The Brits who made the video repeated the procedure but wimped out at consuming the result without having it tested first at a lab.

The video, and video series, in which the segment is embedded, about wild foods, is quite fascinating. But if what you want is the discussion of tubers, it only takes the two minutes.

Unknown said...

Hi Stephen

Am a bit confused. What do you mean when you said: "Fermenting batter doesn't lose minerals because there's nowhere for them to go." Once you have soaked don't the minerals go out in the soak medium at that point? Can you explain for me, please, how does fermenting after soaking retain the minerals? Thanks

angus appleseed said...

"Temperature is also an important factor, with approximately 50 C (122 F) being the optimum."
but elsewhere you wrote
"If you put a lactic acid bacteria starter in the soaking water, it makes it much more effective, as I described in my post "A New Way to Soak Brown Rice". Warming it up speeds the process, although you don't want it to go above 110 F or so because that will kill the phytase."
Am I misunderstanding, or is there a contradiction between the two temperatures given?

Unknown said...

Can you soak in a neutral pH to leach out the tannins, saponins and other anti-nutrients, discard that soak medium and then soak in an acidic pH to reduce the phytic acid content, and then cook in the second soak medium to retain the minerals that leached out during the second soak?