Apparently the negative effects are offset with fermentation and consumption together with meat or fish:
" Soybeans are also high in phytic acid or phytates. This is an organic acid, present in the bran or hulls of all seeds, which blocks the uptake of essential minerals-calcium, magnesium, iron and especially zinc-in the intestinal tract. Although not a household word, phytates have been extensively studied. Scientists are in general agreement that grain and legume based diets high in phytates contribute to widespread mineral deficiencies in third world countries.5 Analysis shows that calcium, magnesium, iron and zinc are present in the plant foods eaten in these areas, but the high phytate content of soy and rice based diets prevents their absorption. The soybean has a higher phytate content than any other grain or legume that has been studied.6 Furthermore, it seems to be highly resistant to many phytate reducing techniques such as long, slow cooking.7 Only a long period of fermentation will significantly reduce the phytate content of soybeans. Thus fermented products such as tempeh and miso provide nourishment that is easily assimilated, but the nutritional value of tofu and bean curd, both high in phytates, is questionable.
When precipitated soy products are consumed with meat, the mineral blocking effects of the phytates are reduced.8 The Japanese traditionally eat tofu as part of a mineral-rich fish broth. Vegetarians who consume tofu and bean curd as a substitute for meat and dairy products risk severe mineral deficiencies. The results of calcium, magnesium and iron deficiency are well known, those of zinc are less so. Zinc is called the intelligence mineral because it is needed for optimal development and functioning of the brain and nervous system. It plays a role in protein synthesis and collagen formation; it is involved in the blood sugar control mechanism and thus protects against diabetes; it is needed for a healthy reproductive system. Zinc is a key component in numerous vital enzymes and plays a role in the immune system. Phytates found in soy products interfere with zinc absorption more completely than with other minerals.9 Literature extolling soy products tends to minimize the role of zinc in human physiology, and to gloss over the deleterious effect of diets high in phytic acid.
Milk drinking is given as the reason second generation Japanese in America grow taller than their native ancestors. Some investigators postulate that the reduced phytate content of the American diet"”whatever may be its other deficiencies-is the true explanation, pointing out that Asian and Oriental children who do not get enough meat and fish products to counteract the effects of a high phytate diet, frequently suffer rickets, stunting and other growth problems.10 The current climate of medical opinion in America has cast a cloud of disapproval on tallness. Parents would do well to ask their six-year-old boys whether they would prefer to be six-foot-one or five-foot-seven when they grow up, before substituting tofu for eggs, meat and dairy products. "
6. El Tiney, A.H., "Proximate Composition and Mineral and Phytate Contents of Legumes Grown in Sudan", Journal of Food Composition and Analysis, v. 2, 1989, pp. 67-78.
7. Ologhobo, A.D., et. al., "Distribution of phosphorus and phytate in some Nigerian varieties of legumes and some effects of processing", J-Food-Sci, v.49 (1), Jan/Feb 1984, pp. 199-201.
8. Sandstrom, B. et. al., "Effect of protein level and protein source on zinc absorption in humans", J-Nutr, v. 119 (1), Jan 1989, pp. 48-53; Tait, Susan, et. al., "The availability of minerals in food, with particular reference to iron", J-R-Soc-Health, v. 103 (2), April 1983, pp. 74-77.
9. Phytate reduction of zinc absorption has been demonstrated in numerous studies; results are summarized in Leviton, Op. Cit, pp. 14-15.
10. Mellanby, Edward, "Experimental rickets: The effect of cereals and their interaction with other factors of diet and environment in producing rickets:", Medical Research Council, v.93, Mar 1925, pp. 2-65; Wills, M.R., et. al., "Phytic Acid and Nutritional Rickets in Immigrants", The Lancet, April 8,1972, pp. 771-773.http://www.westonaprice.org/soy/ploy.html