Phew. That last post really gave the “Wheat Belly” and “should I be reading Carbsane” hornets nests a good kicking. Still no WB book in my mailbox, so time to move on.  Paper of the Week (POTW), this week, belongs to a study that Robb Wolf was given the heads up on, and on which he made a few twitter comments.  As far as I know, he hasn’t analysed it any more formally than that, so I’ll take up the challenge here.  The paper and abstract to set the scene…

Antioxidant and Type 2 Diabetes Related Functional Properties of Phytic Acid Extract from Kenyan Local Food Ingredients: Effects of Traditional Processing Methods

Emerging scientific evidences reveal that phytic acid has several positive effects on human health. The antioxidant and type 2 diabetes related enzyme inhibition properties of phytic acid extract prepared from raw and traditionally processed local grains and vegetables collected from Kenya were evaluated. Phytic acid content of raw grains and vegetables ranged between 2.81–3.01 and 0.29–3.23 g/100 g DM, respectively. The phytic acid extract from raw samples revealed 59%–89% of DPPH radical scavenging capacity, 27–3,526 mmol Fe(II)/g extract of reducing power, 20%–72% of α-amylase inhibition activity and 8%–91% of α-glucosidase inhibition activity. Cooking and roasting improved the antioxidant and health relevant functionality of phytic acid extracts obtained from Kenyan local vegetables and grains, respectively.

Phytic acid (for the nerds: myo-inositol 1,2,3,4,5,6-hexakis-dihydrogen phosphate; IP6), is the main storage form of phosphorus in plants, especially grains, nuts, legumes, and oil seeds, where it can make up 1%-5% of the edible portion. Phytic acid is not digestible to humans or non-ruminant animals, who lack the phytase enzyme (ruminant animals are able to digest it due to their gut bacteria producing enough phytase on their behalf).  Due to this inability to digest phytic acid, we are unable to release the phosphorus for our own nutritional benefit. Furthermore, phytic acid can bind and render unabsorbable certain important minerals such as calcium, magnesium, iron, and zinc.  In addition to this binding of minerals, phytic acid can also bind niacin (vitamin B3), potentially contributing to the deficiency disease pellagra in those cultures that subsist on cereal grains such as corn.  Additionally, I suspect it is possibly phytic acid at work in this study suggesting fibre intake increased vitamin D excretion.

As if that list wasn’t damning enough, our paper of the week highlights another area that should be causing us concern, especially if you have low-nutrient, Standard Western Diet-eating, gastrointestinally-inflammed friends (I got rid of all mine…).  Phytic acid seemingly has the ability to reduce the power of key digestive enzymes.  In the in vitro examples from our paper, phytic acid readily inhibits alpha-amylase and alpha-glucosidase activity, in the order of up to 72% and 91% of activity respectively.  The authors of this paper believe this to be a good thing, as a reduction in the activity of these enzymes could lead to a reduction in post-prandial glucose absorption, which, in their eyes, could be a preventative and/or management strategy for diabetes.  Um… maybe just eating less grains could also be a way of reducing post-prandial glucose? Crazy thought I know…

Plenty has been extensively written on phytic acid already in the paleoesque blogosphere… Here’s three fairly recent examples (you can use your Google-fu to find a few others… go on, I dare ya);

Melissa McEwen – Phytic Acid in Common “Paleo” Foods

Emily Deans – Phytic Acid – Mineral-grubbing Nuisance or Magic Food?

Chris Kresser – Another reason you shouldn’t go nuts on nuts

Chris highlights, in his post above, that phytic acid also inhibits pepsin – the protein-digesting enzyme in your stomach – and trypsin – a protein-digesting enzyme in your small intestine.  One wonders whether phytic acid may also have an effect on fat-digesting lipases? And indeed it seems to do just that. And, in piglets at least, there is evidence that phytic acid might also cause some direct damage to the absorptive capacity of the intestine…

As I’ve been writing this post over a series of days, I now have the full paper to the above piggy study (thanks VP!). From the conclusion;

…dietary [phytic acid] can reduce growth performance and active ion transport in jejunum of piglets. The reduced active ion transport by [phytic acid] implies that the latter reduces the capacity of the small intestine to absorb nutrients. Sodium is absorbed partly by co-transportation with other nutrients and by solvent drag and [phytic acid] has been reported to increase the endogenous flow of [sodium] at terminal ileum of pigs. Thus, the reduced capacity of the small intestine (by phytic acid) to absorb nutrients implies that [phytic acid] increases the ileal endogenous [sodium] flow partly by reducing the re-absorption of endogenously secreted [sodium]. The results also show that dietary [phytic acid] reduces growth performance of pigs partly through reduced capacity of the small intestine to absorb [sodium].

So what happens when all of these enzymes get one hand tied behind their back and the substrates they are supposed to be preparing for absorption, are not absorbed?  Where do they go?  Conjecture alert: I haven’t looked into this, but I wonder if they head south and become a fuel source allowing proliferation of gut bacteria?  Could this process be contributing to colonies of nasty gut gremlins?  I don’t know, but it is perhaps something that is worth further consideration and research.

Emily points out in her post (and the authors of our POTW here believe), that phytic acid might not be all bad… that perhaps its label as an anti-nutrient is a tad unfair.  Like many things within nutrition, it is the dose that makes the poison.  So I am going to stick my neck out and suggest that maybe we should be eating a couple of slices of bread per day – not so much that we get overloaded with phytic acid, but just enough to reap the benefits.

Gotcha!  Not a chance…

Melissa’s post (linked above) points out that many of the foods that we commonly consider to be paleo contain phytic acid (I still much prefer to be talking about neolithic toxins such as grains, sugars, vegetable oils, and industrial soy, rather than which foods are “paleo”).  Indeed, the vegetables tested in the paper under review here (pumpkin, sweet potato, and leafy vegetables), have phytic acid contents ranging from 0.29 to 3.23 g/100g.  The sweet potato and butternut pumpkin were found to possess the highest phytic acid contents among the vegetables, while the leafy vegetables had the lowest.  This is compared to 2.57 to 3.01 g/100g for the analysed grains.

The thing with the vegetables, however, particularly the starchy roots and pumpkins, is that most of the phytic acid occurs in the skin.  In Pacific Island cultures at least, these vegetables have their skins removed prior to cooking.  The following is from links that were left on a recent post looking at Pacific Island diets and the use of coconut cream…

The talo (Colocasia antiquorum) is the staple vegetable food of Samoa. It takes easy precedence over the breadfruit, yam, and sweet potato. Its ceremonial status is high in that it forms the correct vegetable to serve to high chiefs. The talo preparation of fa’ausi is also made the most of in serving before guests. The leaves provide the only green vegetable used. The large ta’amu species is sliced to remove the skin, and never scraped. Slicing removes the astringent and irritating properties more effectively.

The yam. The yam (ufi) though favored as a food, does not enter into the Samoan food complex in the same way as the talo and the breadfruit. It is much scarcer. This is partly due to the greater labor entailed in its cultivation. Its status is high, for one informant coupled it with talo fa’ataisi among the four requisites for a visiting chief’s meal. In his list he retained the drinking coconut and the fowl, but left out the pig, and placed the yam before the talo in order of precedence. It is thus evident that the yam ranked high where pigs were scarce. The yam preparations are exactly similar to those of talo except that fa’ausi was confined to talo.

Our POTW also touches on the effects of processing – whether soaking and cooking reduce the phytic acid content.

Phytic acid is quite stable up to 100°C and it cannot be easily denatured by heat treatment such as that applied in house-hold cooking, roasting, pressure cooking and fermentation.

In this particular study, the soaking and cooking of grains caused no significant losses in the phytic acid content and the enzymatic inhibition effect of those grains.  The authors also point to studies where soaking and cooking actually increased the phytic acid content of some beans and grains.  The phytic acid content of vegetables appears similarly stable during cooking, with the levels only dropping after discarding the cooking water, or if the plants own phytase enzymes are able to degrade the phytic acid within that plant.

So what to draw out of all of this?  Opinion time: whilst there is potential for the small amounts of phytic acid that would occur naturally within a paleo-type diet (via the consumption of starches and leafy vegetables), to have some benefit to health, the larger levels of phytic acid contained within a Standard Western Diet, already relatively limited in nutritional value, and the impact it is having on our digestive and absorptive capacity, is likely to be doing us no favours.  Similar to my observations with histamine, and FODMAP’s, simply “eating-paleo” is no guarantee that there will be a significant decrease in phytic acid intake if consuming lots of nuts and nut flours, seeds, and vegetables (although one should expect that the overall nutrient content of that diet is significantly improved).

The impact of phytic acid on digestive enzymes and the potential for damage to occur directly to the absorptive capacity of the intestine concerns me somewhat more than the binding of minerals, in the context of a mineral-rich paleo diet.  I wholeheartedly disagree with the authors of our POTW that using grains to inhibit starch-degrading enzymes as a treatment strategy for diabetes is an approach worth considering.  I’d rather keep my digestive enzyme capacity intact and look for other strategies to minimise large spikes in blood glucose levels. But I thank them for their concern anyway…

Providing one is consuming plenty of vitamin and mineral-rich meats, “clean” fats (coconut products, saturated animal fats), and tops it off with whatever mix of starchy and non-starchy vegetables match your individual context (peel your starches if you are overly concerned about their phytic acid content), and providing one isn’t trying to replicate all of the foods they miss with paleo clone foods (paleo pizza, paleo brownies, etc), then I can’t see what little phytic acid that would creep into your diet being that much of a problem.

I’ll finish off with a little mini-rant;  I hate gluten… it messes me up when I have it. My health, and the health of others whom I have helped eliminate the stuff from their diets, has done nothing but improve.  However, simply ordering gluten-free bread, gluten-free cakes, biscuits, crackers, and so on, is not eliminating the only problem with these foods.  Many of them still contain sugar, vegetable oils, and plenty of phytic acid – all of which are likely not doing your health any favours.  If you think ordering the likes of French toast or whatever-paleo-food-on-toast, gluten-free, is some sort of get out of jail free card, allowing you to have your cake and eat it to, you are sadly mistaken.