Soy Phytates Inhibit Zinc Absorption

Soybeans may affect brain function because of their phytic acid content. Phytic acid is an organic acid present in the outer portion of all seeds. Also known as phytates, they block the uptake of essential minerals in the intestinal tract: calcium, magnesium, iron, and especially zinc. According to research cited by the Weston A. Price Foundation, soybeans have very high levels of a form of phytic acid that is particularly difficult to neutralize and which interferes with zinc absorption more completely than with other minerals.

The soy industry acknowledges the problem, noting that: “one-half cup of cooked soybeans contains one mg of zinc. However, zinc is poorly absorbed from soyfoods.” As for iron, “both phytate and soy protein reduce iron absorption so that the iron in soyfoods is generally poorly absorbed.” [36]

Nutritionist Sally Fallon, author of Nourishing Traditions: The Cookbook that Challenges Politically Correct Nutrition and the Diet Dictocrats, says that as early as 1967, researchers testing soy formula found that it caused negative zinc balance in every infant to whom it was given. Even when the diets were additionally supplemented with zinc, there was a strong correlation between phytate content in formula and poor growth. She warns that "a reduced rate of growth is especially serious in the infant as it causes a delay in the accumulation of lipids in the myelin, and hence jeopardizes the development of the brain and nervous system."

Zinc and the Brain

Relatively high levels of zinc are found in the brain, especially the hippocampus. Zinc plays an important role in the transmission of the nerve impulse between brain cells. Deficiency of zinc during pregnancy and lactation has been shown to be related to many congenital abnormalities of the nervous system in offspring. In children, "insufficient levels of zinc have been associated with lowered learning ability, apathy, lethargy, and mental retardation." [37]

The USDA references a study of 372 Chinese school children with very low levels of zinc in their bodies. The children who received zinc supplements had the most improved performance - especially in perception, memory, reasoning, and psychomotor skills such as eye-hand coordination. Three earlier studies with adults also showed that changes in zinc intake affected cognitive function. [38]

New research has identified a specific contingent of neurons, called "zinc-containing" neurons, which are found almost exclusively in the forebrain, where in mammals they have evolved into a "complex and elaborate associational network that interconnects most of the cerebral cortices and limbic structures." This suggests the importance of zinc in the normal and pathological processes of the cerebral cortex. [39] Furthermore, age-related tissue zinc deficiency may contribute to brain cell death in Alzheimer's dementia. [40]

Safe Soy

To produce soy milk, the beans are first soaked in an alkaline solution, then heated to about 115 degrees C in order to remove as much of the trypsin inhibitors as possible. Fallon says this method destroys most, but not all of the anti-nutrients, however it has the "unhappy side effect of so denaturing the proteins that they become very difficult to digest and much reduced in effectiveness." Furthermore, phytates remain in soy milk to block the uptake of essential minerals.

Only a long period of fermentation will significantly reduce the phytate content of soybeans, as well as the trypsin inhibitors that interfere with enzymes and amino acids. Therefore, fermented soy products such as tempeh and miso (not tofu) provide nourishment that is easily assimilated.

Excerpt from “The Trouble With Tofu: Soy and the Brain” by John D. MacArthur. For further Information see Soy Online Service - Weston A. Price Foundation http://www.brain.com/about/article.cfm?id=13500&cat_id=37.

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