One of the most common 'anti-nutrients'/organic compounds that alternative health/ancestral diet followers seem to talk about is phytic acid. The structure of phytic acid contains an inositol group (similar to B-vitamin structures) and 6 phosphate groups. Phytic acid exists in plant foods, particularly high in nuts, seeds, whole grains and legumes. Phytic acid is a particularly important reservoir of phosphorous and other mineral cations for a plant - plants contain the enzyme phytase, which can hydrolyze the bonds between phytic acid and its bound minerals (phytic acid:mineral complexes are known as phytates). Humans do not produce phytase, though some bacteria in the human small intestine may have phytase activity, allowing for the release of a small fraction of the bound mineral. The human GI tract's pH, also, does not facilitate the liberation of minerals from their phytate complexes. Phytic acid most commonly binds to non-heme iron, zinc, and calcium (1).
From an evolutionary perspective, phytic acid may have certainly played a selective role throughout hominid evolution, though I have yet to see any genomic research showing evidence of this. Humans have no known evolutionary adaptation to phytic acid in the diet (2). Iron (3) and zinc (4, 5) are both wildly important for fecundity and reproductive success- I would take a gander to say that phytic would've been a much larger issue for early hominids, still focusing largely on their largely plant based diets and utilizing more nuts/seeds/tubers, before scavenging bone marrow and obtaining a significant amount of animal meats via hunting. Captive chimpanzees, especially females, are known to be at risk for iron deficiency anemia and may be given supplements (6). Though little is known in the literature about avoidance of phytic acid, chimps are known to choose foods with lower amounts of tannins (and higher amounts of protein) when available. With the loss of vitamin C synthesis in the Haplorhini suborder of primates via the loss of function for 7 of the 12 exons of the gene, GULOP (L-gluono-1,4-lactone oxidase), I have always wondered whether this was, in any way, related to dietary Vitamin C's ability to increase non-heme iron absorption (7) - if iron bioavailability were playing a selective pressure, there would be a benefit to getting vitamin C through the diet, as opposed to endogenous synthesis. There's little evidence to support this but I digress.
What do we make of phytic acid for the modern person? Phytic acid is certainly something that is considered in the field of nutritional sciences, especially for populations who focus largely on high grain diets. I personally teach in a Nutrition 101 course and we definitely talk about this, alongside oxalates and tannins, as potent mineral inhibitors, and the controversy over the push for more whole grains in the diet. However, I don't entirely understand the Paleo community, whose diet has a large meat component, 's obsession with phytic acid. Meats are excellent sources of bioavailable iron and zinc. Just less than 40% of the iron found in meat is in the heme form. About 15% to 40% of heme iron is absorbed, whereas 1% to 15% of nonheme iron is absorbed (8). The Institute of Medicine has concluded that mixed vegetarian diet's iron content is about 10% bioavailable and mixed Western Diet's iron content is about 18% bioavailable - thus, vegetarians need about 1.8x the iron that omnivorous diets contain (9). The DRI for males (not during puberty) is set at 8mg/day, and 18mg/day for non-menopausal women. It is rather easy for individual's following a Paleo diet to get their iron needs, especially men, despite phytic acid contents- i.e. when I see Paleo forums saying 'avoid nuts because they contain high amounts of phytic acid', i'm a bit confused. Phytic acid should certainly be considered, amongst tannins (coffee/tea intake), vitamin C intake, and calcium supplement intake in the event of a patient with symptoms of iron deficiency anemia or low serum ferritin/high transferrin levels.
But is fearmongering over phytic acid necessary? Meh, you'd be hard pressed to find evidence that supports it. The health consequences of plant based diets' lower bioavailability of iron and zinc has not yet been determined, although should be monitored (10). Even vegetarians, who get no heme iron, can have adequate iron levels (11) and these levels can be improved by both ascorbic acid and iron supplementation (12). This is why the opinion of the Academy of Nutrition and Dietetics has been that a well-planned vegetarian diet is adequate (13). Jack Norris wrote a great article (with citations) on vegetarians and iron, and shows that those who should be most concerned with iron are pregnant and pre-menopausal women - vegetarian or not, and that vegetarian men generally do not show signs of abnormal iron status (24). Consumption of fermented and soaked/sprouted foods also reduces the amount of phytate in foods (14). I, personally, get a significant amount of my dietary iron from tempeh, a fermented soybean cake.
This fearmongering also ignores the other half of the phytic acid story. Phytic acid has been implicated in a number of anti-cancer mechanisms, enhancement of the immune system, prevention of pathological calcification and kidney stone formation, lowering of elevated serum cholesterol, and reduction of pathological platelet activity (15, 16).
The focus on phytic acid seems to be a response to the push for largely plant based diets, which I don't entirely disagree with. Consuming a plant-based diet may lead to sub-optimal levels of some minerals, and this must be something that is weighed in the event of someone choosing a high-fiber/plant based diet. However, what is also not talked about too much by the Paleo diet is the cytotoxic effects of heme iron and the oxidative effects of dietary iron. As with mostly everything in physiology, anything below or above homeostasis is generally not great for you: iron deficiency is obviously a problem but excess amounts of iron may promote oxidation. Iron has been shown to play a potent role in the development and proliferation of cancer (17). Heme iron and meat intake also directly increase the risk of colonic, liver and endometrial cancers (18, 19). A great read of the mechanisms on this can be found here (20). However, chlorophyll and calcium salts have been shown to arrest this cytotoxic environment (21, 22, 23). Just as chlorophyll can arrest the cytotoxic environment induced by heme, phytic acid can bind iron and prevent it's pro-oxidant reactivity throughout the gut. The interactions between all of these definitely need further research before a clear statement and recommendation about the amount of heme iron consumed can be made.
What's my end take on all of this? If you're consuming red meats and fish, phytic acid is not your biggest concern - someone on a Paleo-style diet, as long as their serum ferritin levels look fine, doesn't have much to worry about. If you're consuming a largely plant based diet, make sure your iron levels are OK- look out for signs of iron deficiency such as fatigue and being easily bruised. Focus on choosing vitamin C rich foods while consuming your major sources of iron and avoid coffee/tea around meal times. Phytic acid is a concern, but it is certainly not a reason to avoid foods. Seeing articles saying "don't eat nuts/seeds/legumes because they contain phytic acid" is ridiculous and is entirely unfounded/unsupported by the scientific literature.
(http://sickle.bwh.harvard.edu/iron_absorption.html)
1. Lucock, Mark. Molecular Nutrition and Genomics: nutrition and the ascent of humankind. 2007. Wiley.
2.http://www.ncbi.nlm.nih.gov/pubmed/2538051
3. http://www.ncbi.nlm.nih.gov/pubmed/23571830
4. http://www.ncbi.nlm.nih.gov/pubmed/23847261
5. http://www.ncbi.nlm.nih.gov/pubmed/19285597
6. Fulk, R., M. Loomis and C. Garland (1992) Nutrition of captive chimpanzees. In: The care and management of chimpanzees in captive environments. Chimpanzee Species Survival Plan – Husbandry Manual. Fulk, R. and C. Garland, Eds. American Association of Zoos and Aquariums
7. http://ajcn.nutrition.org/content/73/1/93.full
8. Hunt JR. Bioavailability of iron, zinc and other trace minerals from vegetarian diets. Am J Clin Nutr. 2003;78(suppl):633S-639S.
9. Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academies Press; 2003.
10. http://ajcn.nutrition.org/content/78/3/633S.abstract
11. http://ajcn.nutrition.org/content/59/5/1233S.abstract
12. http://www.ncbi.nlm.nih.gov/pubmed/8582755
13. http://www.eatright.org/About/Content.aspx?id=8357
14. http://www.ncbi.nlm.nih.gov/pubmed/1654732
15. http://www.ncbi.nlm.nih.gov/pubmed/22993910
16. http://www.ncbi.nlm.nih.gov/pubmed/17044765
17. http://www.nature.com/nrc/journal/v13/n5/full/nrc3495.html
18. http://www.ncbi.nlm.nih.gov/pubmed/21209396
19. http://www.ncbi.nlm.nih.gov/pubmed/22952183
20 Red meat and colon cancer: the cytotoxic and hyperproliferative effects of dietary heme
Aloys L.A. Sesink, Denise S.M.L. Termont, Jan H. Kleibeuker, and Roelof Van der Meer Cancer Research 59, 5704-5709, 1999
21.http://jn.nutrition.org/content/135/8/1995.abstract
22. http://carcin.oxfordjournals.org/content/22/10/1653.abstract
23. http://cebp.aacrjournals.org/content/15/4/717.abstract
24. http://www.veganhealth.org/articles/iron
From an evolutionary perspective, phytic acid may have certainly played a selective role throughout hominid evolution, though I have yet to see any genomic research showing evidence of this. Humans have no known evolutionary adaptation to phytic acid in the diet (2). Iron (3) and zinc (4, 5) are both wildly important for fecundity and reproductive success- I would take a gander to say that phytic would've been a much larger issue for early hominids, still focusing largely on their largely plant based diets and utilizing more nuts/seeds/tubers, before scavenging bone marrow and obtaining a significant amount of animal meats via hunting. Captive chimpanzees, especially females, are known to be at risk for iron deficiency anemia and may be given supplements (6). Though little is known in the literature about avoidance of phytic acid, chimps are known to choose foods with lower amounts of tannins (and higher amounts of protein) when available. With the loss of vitamin C synthesis in the Haplorhini suborder of primates via the loss of function for 7 of the 12 exons of the gene, GULOP (L-gluono-1,4-lactone oxidase), I have always wondered whether this was, in any way, related to dietary Vitamin C's ability to increase non-heme iron absorption (7) - if iron bioavailability were playing a selective pressure, there would be a benefit to getting vitamin C through the diet, as opposed to endogenous synthesis. There's little evidence to support this but I digress.
What do we make of phytic acid for the modern person? Phytic acid is certainly something that is considered in the field of nutritional sciences, especially for populations who focus largely on high grain diets. I personally teach in a Nutrition 101 course and we definitely talk about this, alongside oxalates and tannins, as potent mineral inhibitors, and the controversy over the push for more whole grains in the diet. However, I don't entirely understand the Paleo community, whose diet has a large meat component, 's obsession with phytic acid. Meats are excellent sources of bioavailable iron and zinc. Just less than 40% of the iron found in meat is in the heme form. About 15% to 40% of heme iron is absorbed, whereas 1% to 15% of nonheme iron is absorbed (8). The Institute of Medicine has concluded that mixed vegetarian diet's iron content is about 10% bioavailable and mixed Western Diet's iron content is about 18% bioavailable - thus, vegetarians need about 1.8x the iron that omnivorous diets contain (9). The DRI for males (not during puberty) is set at 8mg/day, and 18mg/day for non-menopausal women. It is rather easy for individual's following a Paleo diet to get their iron needs, especially men, despite phytic acid contents- i.e. when I see Paleo forums saying 'avoid nuts because they contain high amounts of phytic acid', i'm a bit confused. Phytic acid should certainly be considered, amongst tannins (coffee/tea intake), vitamin C intake, and calcium supplement intake in the event of a patient with symptoms of iron deficiency anemia or low serum ferritin/high transferrin levels.
But is fearmongering over phytic acid necessary? Meh, you'd be hard pressed to find evidence that supports it. The health consequences of plant based diets' lower bioavailability of iron and zinc has not yet been determined, although should be monitored (10). Even vegetarians, who get no heme iron, can have adequate iron levels (11) and these levels can be improved by both ascorbic acid and iron supplementation (12). This is why the opinion of the Academy of Nutrition and Dietetics has been that a well-planned vegetarian diet is adequate (13). Jack Norris wrote a great article (with citations) on vegetarians and iron, and shows that those who should be most concerned with iron are pregnant and pre-menopausal women - vegetarian or not, and that vegetarian men generally do not show signs of abnormal iron status (24). Consumption of fermented and soaked/sprouted foods also reduces the amount of phytate in foods (14). I, personally, get a significant amount of my dietary iron from tempeh, a fermented soybean cake.
This fearmongering also ignores the other half of the phytic acid story. Phytic acid has been implicated in a number of anti-cancer mechanisms, enhancement of the immune system, prevention of pathological calcification and kidney stone formation, lowering of elevated serum cholesterol, and reduction of pathological platelet activity (15, 16).
The focus on phytic acid seems to be a response to the push for largely plant based diets, which I don't entirely disagree with. Consuming a plant-based diet may lead to sub-optimal levels of some minerals, and this must be something that is weighed in the event of someone choosing a high-fiber/plant based diet. However, what is also not talked about too much by the Paleo diet is the cytotoxic effects of heme iron and the oxidative effects of dietary iron. As with mostly everything in physiology, anything below or above homeostasis is generally not great for you: iron deficiency is obviously a problem but excess amounts of iron may promote oxidation. Iron has been shown to play a potent role in the development and proliferation of cancer (17). Heme iron and meat intake also directly increase the risk of colonic, liver and endometrial cancers (18, 19). A great read of the mechanisms on this can be found here (20). However, chlorophyll and calcium salts have been shown to arrest this cytotoxic environment (21, 22, 23). Just as chlorophyll can arrest the cytotoxic environment induced by heme, phytic acid can bind iron and prevent it's pro-oxidant reactivity throughout the gut. The interactions between all of these definitely need further research before a clear statement and recommendation about the amount of heme iron consumed can be made.
What's my end take on all of this? If you're consuming red meats and fish, phytic acid is not your biggest concern - someone on a Paleo-style diet, as long as their serum ferritin levels look fine, doesn't have much to worry about. If you're consuming a largely plant based diet, make sure your iron levels are OK- look out for signs of iron deficiency such as fatigue and being easily bruised. Focus on choosing vitamin C rich foods while consuming your major sources of iron and avoid coffee/tea around meal times. Phytic acid is a concern, but it is certainly not a reason to avoid foods. Seeing articles saying "don't eat nuts/seeds/legumes because they contain phytic acid" is ridiculous and is entirely unfounded/unsupported by the scientific literature.
| Physical State (bioavailability) | heme > Fe2+ > Fe3+ |
| Inhibitors | phytates, tannins, soil clay, laundry starch, iron overload, antacids |
| Competitors | lead, cobalt, strontium, manganese, zinc |
| Facilitators | ascorbate, citrate, amino acids, iron deficiency |
(http://sickle.bwh.harvard.edu/iron_absorption.html)
1. Lucock, Mark. Molecular Nutrition and Genomics: nutrition and the ascent of humankind. 2007. Wiley.
2.http://www.ncbi.nlm.nih.gov/pubmed/2538051
3. http://www.ncbi.nlm.nih.gov/pubmed/23571830
4. http://www.ncbi.nlm.nih.gov/pubmed/23847261
5. http://www.ncbi.nlm.nih.gov/pubmed/19285597
6. Fulk, R., M. Loomis and C. Garland (1992) Nutrition of captive chimpanzees. In: The care and management of chimpanzees in captive environments. Chimpanzee Species Survival Plan – Husbandry Manual. Fulk, R. and C. Garland, Eds. American Association of Zoos and Aquariums
7. http://ajcn.nutrition.org/content/73/1/93.full
8. Hunt JR. Bioavailability of iron, zinc and other trace minerals from vegetarian diets. Am J Clin Nutr. 2003;78(suppl):633S-639S.
9. Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academies Press; 2003.
10. http://ajcn.nutrition.org/content/78/3/633S.abstract
11. http://ajcn.nutrition.org/content/59/5/1233S.abstract
12. http://www.ncbi.nlm.nih.gov/pubmed/8582755
13. http://www.eatright.org/About/Content.aspx?id=8357
14. http://www.ncbi.nlm.nih.gov/pubmed/1654732
15. http://www.ncbi.nlm.nih.gov/pubmed/22993910
16. http://www.ncbi.nlm.nih.gov/pubmed/17044765
17. http://www.nature.com/nrc/journal/v13/n5/full/nrc3495.html
18. http://www.ncbi.nlm.nih.gov/pubmed/21209396
19. http://www.ncbi.nlm.nih.gov/pubmed/22952183
20 Red meat and colon cancer: the cytotoxic and hyperproliferative effects of dietary heme
Aloys L.A. Sesink, Denise S.M.L. Termont, Jan H. Kleibeuker, and Roelof Van der Meer Cancer Research 59, 5704-5709, 1999
21.http://jn.nutrition.org/content/135/8/1995.abstract
22. http://carcin.oxfordjournals.org/content/22/10/1653.abstract
23. http://cebp.aacrjournals.org/content/15/4/717.abstract
24. http://www.veganhealth.org/articles/iron
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