It is time to look at another common rumor regarding soy foods; the dangers posed by phytates. Phytate is the name for the salt form of phytic acid, a phosphorus containing molecule in many plant tissues.
The Weston A. Price Foundation writes, “High levels of phytic acid in soy reduce assimilation of calcium, magnesium, copper, iron and zinc. Phytic acid in soy is not neutralized by ordinary preparation methods such as soaking, sprouting and long, slow cooking. High phytate diets have caused growth problems in children.”
The “natural health” website Mercola writes, “Soy contains phytates. Phytates (phytic acid) bind to metal ions, preventing the absorption of certain minerals, including calcium, magnesium, iron, and zinc -- all of which are co-factors for optimal biochemistry in your body. This is particularly problematic for vegetarians, because eating meat reduces the mineral-blocking effects of these phytates (so it is helpful—if you do eat soy—to also eat meat).”
Soy Online Service adds, “Soybeans contain very high levels of phytate and their[sic] are numerous reports of reduced bioavailablity[sic] of various metals from foods containing soy; this has particular significance for vegetarians and infants fed soy-formulas.”
We already learned from last year's post on The Dangers of Phytoestrogens that, “Comprehensive literature reviews and clinical studies of infants fed SBIFs[soy based infant formulas] have resolved questions or raise no clinical concerns with respect to nutritional adequacy, sexual development, neurobehavioral development, immune development, or thyroid disease. SBIFs provide complete nutrition that adequately supports normal infant growth and development.” Interestingly however, there is still quite a bit of truth to these concerns over phytate. Soy does contain phytate and phytate does reduce our absorption of several minerals.
There is one redeeming aspect to all of this however. Soy is not a particularly exceptional source of phytate. The 2001 book Food Phytates brought together a lot of information about phytates and published it in a very convenient fashion. Part of this book involved gathering data on quantity of phytate in various foods and arranging that into a convenient table. Here are a few bits of data from that table:
Source - %Phytate by mass
Dolique Beans – 5.92-9.15%
Brazil Nut – 1.97-6.34%
Almond – 1.35-3.22%
Tofu – 1.46-2.90%
Linseed – 2.15-2.78%
Pinto Beans – 0.61-2.38%
Soybeans – 1.00-2.22%
Peanuts – 1.05-1.76%
Kidney Beans – 0.89-1.57%
Tempe – 0.67-1.08%
Soy Milk – 0.05-0.11%
Do keep in mind that you probably consume much more soy milk by mass than you would soybeans or almonds. The book also mentions that, “Dry cereals account for 69.5% of the total global crop seeds/grains/fruit each year but synthesized 77.3% of the total PA [Phytic Acid]. Legumes account for 7.6% of the annual global production of crop seeds/grains/fruits and 13.0% of the total PA.” I encourage you to look through the entire table for yourself, which is available via Google Books.
The American Dietetic Association in their position paper regarding vegan and vegetarian diets brings up phytic acid or phytate several times, regarding calcium, zinc, and iron.
One recent study attempted to measure the absorption of calcium and zinc in Nigerian children with and without rickets. In the study the authors, “sought to examine 1) the effect of a typical Nigerian meal on the absorption of zinc and calcium 2), the effect of meal dephytinization on calcium and zinc absorption, and 3) whether the relationships between mineral absorption, meal consumption, and dephytinization were different in children with and without rickets.” Dephytinization is the word for removing phytate from a substance. The study authors went about this by giving the study participants a bowl of porridge along with a cup of orange juice fortified with both calcium and zinc to be consumed half way through. They repeated this process with both regular and phytate reduced porridges. While the study was largely about rickets, those findings had no detectable effect on the results. “Calcium absorption did not differ significantly between children with and without rickets for any permutation of meal.” Interestingly, they also note that the phytic acid had no significant impact on calcium absorption either. “Calcium absorption with fermented[phytate reduced] porridge (50.7 ± 19.1%) did not differ from unfermented porridge (50.1 ± 17.3%; P = 0.94).” The study also found rickets to have no detectable effect on zinc absorption. It did however find that dephytinization had a significant impact. “Enzymatic dephytinization increased zinc absorption during the second absorption study (55.5 ± 18.0% vs. 32.2 ± 14.8%; P < 0.001). Dephytinization resulted in a mean relative increase in zinc absorption of 101 ± 88%.” This study suggests that phytic acid has at most a modest impact on calcium absorption, but may affect the absorption of zinc fairly significantly.
The effect of phytic acid on iron absorption has been much more thoroughly studied. One study attempted to model iron absorption based off a number of factors and was able to achieve an r^2 value of .987 (usually interpreted as 98.7% of the variation in iron absorption rates could be accounted for by their model). The two main terms in their model were phytic acid content and ascorbic acid content (more commonly known as vitamin C). Their model found that the ratio of iron that was absorbed from an ordinary wheat roll increased linearly with the amount of ascorbic acid, decreased with the logarithm of phytic acid content. This means that as vitamin c increases the rate of iron absorption continues to increase at a similar rate, while as phytic acid increases it has a diminishing impact on the amount it inhibits absorption. Overall however, if you look at absorption from the vegetarian meals they studied the absorption of iron in those meals was still much lower than absorption from meat-containing meals. Perhaps this is why the American Dietetic Association suggests, “because of lower bioavailability of iron from a vegetarian diet, the recommended iron intakes for vegetarians are 1.8 times those of nonvegetarians.”
So while soy certainly isn't a guilty culprit, phytic acid absolutely has a negative impact on our absorption of minerals as vegetarians. What, however, is the net impact of all this on overall health? Perhaps a paper titled Health Effects of Vegan Diets in the American Journal of Clinical Nutrition can help answer this for us.
“[T]he risk of iron deficiency anemia are similar for vegans compared with omnivores and other vegetarians. Vegans often consume large amounts of vitamin C–rich foods that markedly improve the absorption of the nonheme iron.”
“Phytates, a common component of grains, seeds, and legumes, binds zinc and thereby decreases its bioavailability. However, a sensitive marker to measure zinc status in humans has not been well established, and the effects of marginal zinc intakes are poorly understood. Although vegans have lower zinc intake than omnivores, they do not differ from the nonvegetarians in functional immunocompetence as assessed by natural killer cell cytotoxic activity. It appears that there may be facilitators of zinc absorption and compensatory mechanisms to help vegetarians adapt to a lower intake of zinc.”
“More recent studies with postmenopausal Asian women showed spine or hip BMD was significantly lower in long-term vegans. Those Asian women, who were vegetarian for religious reasons, had low intakes of protein and calcium. […] The higher risk of bone fracture seen in vegans appears to be a consequence of a lower mean calcium intake. No difference was observed between the fracture rates of the vegans who consumed >525 mg calcium/d and the omnivore fracture rates.”
Overall it seems that our lower rates of absorption of zinc and iron are accounted for by higher intakes of those minerals. Getting enough calcium can be a concern for some vegans, but for those who do they seem to utilize it just fine. If there is one thing to take away from all this, I think the American Dietetic Association summarizes it best. “[A]ppropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthful, nutritionally adequate, and may provide health benefits in the prevention and treatment of certain diseases. Well-planned vegetarian diets are appropriate for individuals during all stages of the life cycle, including pregnancy, lactation, infancy, childhood, and adolescence, and for athletes.”
Plan your diet well, eat a healthy variety of foods, and no, eating soy is not going to kill you.
Showing posts with label soy dangers. Show all posts
Showing posts with label soy dangers. Show all posts
Tuesday, October 12, 2010
Monday, November 2, 2009
Dangers of Phytoestrogens
Today we are going to turn our skeptical eye on the proclaimed dangers of phytoestrogens. What are phytoestrogens? Phytoestrogens are compounds, which due to their similarity to the estrogen estradiol used in our own bodies, are able to cause mild estrogenic or antiestrogenic effects. Phytoestrogens appear in many foods including soy, flax, sesame seeds, wheat, rice, apples, carrots, and many other foods. Opponents claim that because of the high concentration of these compounds in soy, eating soy foods at the levels present in our society is highly dangerous and causing a multitude of undesirable effects. SoyOnlineService.co.nz claims:
“Phytoestrogens that disrupt endocrine function and are potent antithyroid agents are present in vast quantities in soy, including the potentially devastating isoflavone Genistein. Infants exclusively fed soy-based formula have 13,000 to 22,000 times more estrogen compounds in their blood than babies fed milk-based formula, the estrogenic equivalent of at least five birth control pills per day.”
FoodRenegade.com claims:
“An infant taking the recommended amount of soy formula is consuming a hormone load equivalent of 4 birth control pills a day!”
Finally WestonAPrice.org claims:
“A recent study found that babies fed soy-based formula had 13,000 to 22,0000 times more isoflavones in their blood than babies fed milk-based formula.”
Which, if any, of these differing claims is true? While none of these websites cite sources, I was able to track down the original source of this claim published in The Lancet journal in 1997:
“Circulating concentrations of isoflavones in the seven infants fed soy-based formula were 13000-22000 times higher than plasma oestradiol concentrations in early life, and may be sufficient to exert biological effects, whereas the contribution of isoflavones from breast-milk and cow-milk is negligible.” Link
Note that this is not 13,000-22,000 times more isoflavones than non-milk fed infants or 13,000-22,000 times more estrogen compounds. This is stating that circulating isoflavone concentrations are 13,000-22,000 times higher than plasma oestradiol concentrations. Without some way to compare isoflavone concentrations to plasma oestradiol concentrations this is as meaningful as stating that saturated fat intake is thousands of times higher than vitamin B12 intake. How do isoflavones compare to estradiol?
Comparisons between isoflavones and estrogens are extremely complex. All isoflavones bond to human estrogen receptors extremely weakly. Of isoflavones, genistein binds most strongly, but it is still very weak relative to most estrogens. All isoflavones bond better to beta type estrogen receptors than alpha type receptors. For beta type receptors genistein binds almost as strongly as estradiol; although estradiol is about 10,000 times more potent at inducing transcription from this receptor.
“Even if genistein bound as efficiently as 17 beta -estradiol, the structural transformation of hER[human estrogen receptor] beta induced by genistein would not be sufficient to facilitate the binding of a coactivator. The induction of transcription by ERs[estrogen receptors] requires a coactivator.”
This study can be found here
Infants using soy formula generally take in about 4mg/kg/day in isoflavones. This includes both genistein and weaker isoflavones like daidzein. For an infant weighing 5kg, this would mean 20mg of isoflavones are taken in every day. How does this compare to birth control pills? Birth control uses both estrogen and progesterone to achieve its effects. Comparing to only estrogen is leaving out an important ingredient in the pill; however, pills vary from about 20mcg (.02mg) to about 50mcg (.05mg) of estrogen in the pills. Even if we assume that all of the isoflavones ingested by infants are the more strongly acting genistein, that genistein binds to beta receptors as strongly as estradiol, and that alpha receptors can be ignored entirely, the isoflavones ingested would still only be 1/10th to 1/25th of the equivalent of just the estrogen in a birth control pill, and all of these estimates are overly generous.
While the claims made by these anti-soy websites are either incredibly misleading or downright false, this says nothing about the actual safety of phytoestrogens. What impacts have phytoestrogens been found to have on human bodies?
From 1965 to 1975 the University of Iowa ran a controlled feeding study in which 248 infants were fed soy formula and 563 were fed dairy formula. Between March and August 1999 the now adults who had participated in this study were tracked down and asked to report on time of pubertal maturation, menstrual and reproductive history, height and usual weight, and current health.
“No statistically significant differences were observed between groups in either women or men for more than 30 outcomes. However, women who had been fed soy formula reported slightly longer duration of menstrual bleeding (adjusted mean difference, 0.37 days; 95% confidence interval [CI], 0.06-0.68), with no difference in severity of menstrual flow.”
The study concluded,
“Exposure to soy formula does not appear to lead to different general health or reproductive outcomes than exposure to cow milk formula. Although the few positive findings should be explored in future studies, our findings are reassuring about the safety of infant soy formula.”
This study was published in the Journal of the American Medical Association in 2001 and can be found here
A review of the literature on soy based infant formulas was published in the Journal of Nutrition in 2004 and concluded,
“SBIF[Soy-based infant formula] is well recognized as a healthy alternative to human or cow’s milk. It has a long history of safe use and is a high-quality, plant-based protein alternative for infant formula. Recent in-depth reviews of the safety of dietary isoflavones in soy have found that there is no conclusive evidence from animal or human adult or infant populations that indicates that dietary isoflavones may adversely affect human health development or reproduction. Comprehensive literature reviews and clinical studies of infants fed SBIFs have resolved questions or raise no clinical concerns with respect to nutritional adequacy, sexual development, neurobehavioral development, immune development, or thyroid disease. SBIFs provide complete nutrition that adequately supports normal infant growth and development.”
The entirety of this article can be found here
Currently, the Arkansas Children's Nutrition Center is conducting a longitudinal study comparing growth, development, and health of breastfed children with soy formula-fed and dairy formula-fed children from birth through age 6 y. “After 5 y of study, children in all 3 groups (n > 300) are growing and developing within normal limits, and there are no indications of adverse effects in the soy-fed children.” This study, published in the American Journal of Clinical Nutrition, can be found here
Most of the research on isoflavone use later in life has to do with breast cancer risk in postmenopausal women. Most research tends to conclude there is a reduced risk since the isoflavone genistein is antiangiogenic (blocks the formation of new arteries); although, for certain types of estrogen dependent breast cancers, slightly higher risks have been associated with higher isoflavone intake. Other cancers such as prostate and cervical cancer are less frequent with higher isoflavone intake, likely due to the antiangiogenic effects of the isoflavones. Isoflavones also tend to act as antioxidants, preventing free-radicals from causing damage to cells.
While a great deal of research can still be done to work out the details, soy and other phytoestrogen containing foods have and continue to be used in differing quantities throughout the world, and no evidence exists to suggest these phytoestrogens pose significant health risks to healthy adult or developing humans. Next time you hear clearly misquoted claims proclaiming the severe health risks of a common food on a poorly sourced website, remember to be skeptical!
Check out the new post on the dangers of phytates.
“Phytoestrogens that disrupt endocrine function and are potent antithyroid agents are present in vast quantities in soy, including the potentially devastating isoflavone Genistein. Infants exclusively fed soy-based formula have 13,000 to 22,000 times more estrogen compounds in their blood than babies fed milk-based formula, the estrogenic equivalent of at least five birth control pills per day.”
FoodRenegade.com claims:
“An infant taking the recommended amount of soy formula is consuming a hormone load equivalent of 4 birth control pills a day!”
Finally WestonAPrice.org claims:
“A recent study found that babies fed soy-based formula had 13,000 to 22,0000 times more isoflavones in their blood than babies fed milk-based formula.”
Which, if any, of these differing claims is true? While none of these websites cite sources, I was able to track down the original source of this claim published in The Lancet journal in 1997:
“Circulating concentrations of isoflavones in the seven infants fed soy-based formula were 13000-22000 times higher than plasma oestradiol concentrations in early life, and may be sufficient to exert biological effects, whereas the contribution of isoflavones from breast-milk and cow-milk is negligible.” Link
Note that this is not 13,000-22,000 times more isoflavones than non-milk fed infants or 13,000-22,000 times more estrogen compounds. This is stating that circulating isoflavone concentrations are 13,000-22,000 times higher than plasma oestradiol concentrations. Without some way to compare isoflavone concentrations to plasma oestradiol concentrations this is as meaningful as stating that saturated fat intake is thousands of times higher than vitamin B12 intake. How do isoflavones compare to estradiol?
Comparisons between isoflavones and estrogens are extremely complex. All isoflavones bond to human estrogen receptors extremely weakly. Of isoflavones, genistein binds most strongly, but it is still very weak relative to most estrogens. All isoflavones bond better to beta type estrogen receptors than alpha type receptors. For beta type receptors genistein binds almost as strongly as estradiol; although estradiol is about 10,000 times more potent at inducing transcription from this receptor.
“Even if genistein bound as efficiently as 17 beta -estradiol, the structural transformation of hER[human estrogen receptor] beta induced by genistein would not be sufficient to facilitate the binding of a coactivator. The induction of transcription by ERs[estrogen receptors] requires a coactivator.”
This study can be found here
Infants using soy formula generally take in about 4mg/kg/day in isoflavones. This includes both genistein and weaker isoflavones like daidzein. For an infant weighing 5kg, this would mean 20mg of isoflavones are taken in every day. How does this compare to birth control pills? Birth control uses both estrogen and progesterone to achieve its effects. Comparing to only estrogen is leaving out an important ingredient in the pill; however, pills vary from about 20mcg (.02mg) to about 50mcg (.05mg) of estrogen in the pills. Even if we assume that all of the isoflavones ingested by infants are the more strongly acting genistein, that genistein binds to beta receptors as strongly as estradiol, and that alpha receptors can be ignored entirely, the isoflavones ingested would still only be 1/10th to 1/25th of the equivalent of just the estrogen in a birth control pill, and all of these estimates are overly generous.
While the claims made by these anti-soy websites are either incredibly misleading or downright false, this says nothing about the actual safety of phytoestrogens. What impacts have phytoestrogens been found to have on human bodies?
From 1965 to 1975 the University of Iowa ran a controlled feeding study in which 248 infants were fed soy formula and 563 were fed dairy formula. Between March and August 1999 the now adults who had participated in this study were tracked down and asked to report on time of pubertal maturation, menstrual and reproductive history, height and usual weight, and current health.
“No statistically significant differences were observed between groups in either women or men for more than 30 outcomes. However, women who had been fed soy formula reported slightly longer duration of menstrual bleeding (adjusted mean difference, 0.37 days; 95% confidence interval [CI], 0.06-0.68), with no difference in severity of menstrual flow.”
The study concluded,
“Exposure to soy formula does not appear to lead to different general health or reproductive outcomes than exposure to cow milk formula. Although the few positive findings should be explored in future studies, our findings are reassuring about the safety of infant soy formula.”
This study was published in the Journal of the American Medical Association in 2001 and can be found here
A review of the literature on soy based infant formulas was published in the Journal of Nutrition in 2004 and concluded,
“SBIF[Soy-based infant formula] is well recognized as a healthy alternative to human or cow’s milk. It has a long history of safe use and is a high-quality, plant-based protein alternative for infant formula. Recent in-depth reviews of the safety of dietary isoflavones in soy have found that there is no conclusive evidence from animal or human adult or infant populations that indicates that dietary isoflavones may adversely affect human health development or reproduction. Comprehensive literature reviews and clinical studies of infants fed SBIFs have resolved questions or raise no clinical concerns with respect to nutritional adequacy, sexual development, neurobehavioral development, immune development, or thyroid disease. SBIFs provide complete nutrition that adequately supports normal infant growth and development.”
The entirety of this article can be found here
Currently, the Arkansas Children's Nutrition Center is conducting a longitudinal study comparing growth, development, and health of breastfed children with soy formula-fed and dairy formula-fed children from birth through age 6 y. “After 5 y of study, children in all 3 groups (n > 300) are growing and developing within normal limits, and there are no indications of adverse effects in the soy-fed children.” This study, published in the American Journal of Clinical Nutrition, can be found here
Most of the research on isoflavone use later in life has to do with breast cancer risk in postmenopausal women. Most research tends to conclude there is a reduced risk since the isoflavone genistein is antiangiogenic (blocks the formation of new arteries); although, for certain types of estrogen dependent breast cancers, slightly higher risks have been associated with higher isoflavone intake. Other cancers such as prostate and cervical cancer are less frequent with higher isoflavone intake, likely due to the antiangiogenic effects of the isoflavones. Isoflavones also tend to act as antioxidants, preventing free-radicals from causing damage to cells.
While a great deal of research can still be done to work out the details, soy and other phytoestrogen containing foods have and continue to be used in differing quantities throughout the world, and no evidence exists to suggest these phytoestrogens pose significant health risks to healthy adult or developing humans. Next time you hear clearly misquoted claims proclaiming the severe health risks of a common food on a poorly sourced website, remember to be skeptical!
Check out the new post on the dangers of phytates.
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