Answers to the Myths of the Dangers of Soy

BY Laura H. Hatton, M.S., C.C.N., C.P.T., ACHS Instructor

Recently there has been a lot of information being published purporting the evils of soy. I have been very concerned about this information and responded to a specific set of myths that were published on a popular website. The following is a summary of that research.

Myth #1―High levels of phytic acid in soy reduce the assimilation of calcium, magnesium, copper, iron, and zinc. Phytic acid is not neutralized by ordinary preparation methods such as soaking, sprouting and long, slow cooking. High phytate diets cause growth problems in children.

First off, all beans and grains have phytates. We understand this and are instructed to cook our beans and grains well and never eat raw. Second, assimilation is only potentially compromised in zinc and iron, as well as some calcium and magnesium. It has never been shown to interfere with copper absorption. However, though the possibility of this occurring is seen to interfere with the growth and mineral status of animals, it has never been seen in humans. In several studies done on humans there was no evidence of compromised absorption of any of these metals.

Sprouting has been shown to reduce phytate levels and fermentation is very helpful in this. Tempeh has ½-⅔ the phytate content of regular soybeans.[1] Also, cooking, germination, fermentation, soaking, and autolysis have been shown to decrease the inhibitory effect of phytic acid on mineral absorption.[2] Another important study noted that prebiotics and probiotics promote degradation of phytates in the gut.[3] Thus, it is very important to have very healthy gut flora to improve digestion of soy.

Myth #2―Trypsin inhibitors in soy interfere with protein digestion and may cause pancreatic disorders. In test animals soy containing trypsin inhibitors caused stunted growth.

Although studies have shown these adverse effects in rats, other studies showed no effect on mice or hamsters. Trypsin inhibitors are sensitive to heat. Therefore, most of their activity is lost when raw soybeans are exposed to heat.

As Liener explains, “Most commercially available soybean products intended for human consumption, such as tofu, soy milk, soy-based infant formula, soy protein isolates and concentrates, and textured meat analogs, have received sufficient heat treatment to cause inactivation of at least 80% of the trypsin inhibitor activity present in raw soybeans. This level of trypsin inhibitor destruction is well above the threshold level of 50-60% inactivation found to be necessary for eliminating significant growth inhibition and pancreatic hypertrophy."[4]

In addition, “All antinutritional factors such as phytic acid, tannin, trypsin inhibitor.. are decreased during soaking in 0.5% sodium bicarbonate.” In other words, soaking beans in a little baking soda will help reduce these things. “Human trypsin is more resistant to inhibition than is the trypsin of other mammalian species. The effect on human trypsin of soybean trypsin inhibition in soy protein does not appear to be a potential hazard to man.”

>> For information about more soy myths, download the full-length article in the March edition of the ACHS holistic health eNewsletter, the ACHS Reporter: http://www.achs.edu/newsletter.aspx?id=7

References:
[1] Liener IE. (1994). Implications of Antinutritional Components in Soybean Foods. Crit Rev Food Sci Nutr, 34(1):31-67.
[2] Urbano G. (2000). Lopez-Jurado M, et al. The Role of Phytic Acid in Legumes: antinutrient or beneficial function. J Physiol Biochem, 56(3):283-94.
[3] Scholz-Ahrens KE; Ade P; et al. (2007). Prebiotics, probiotics, and synbiotics affect mineral absorption, bone mineral content, and bone structure. J Nutr, 137(3 Suppl 2):838S-46S.
[4] Liener IE. (1994). Implications of Antinutritional Components in Soybean Foods. Crit Rev Food Sci Nutr, 34(1):31-67.

Image (c) http://upload.wikimedia.org/wikipedia/commons/8/82/Soybean.USDA.jpg