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. 
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." 
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. 
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.  Furthermore, age-related tissue zinc deficiency
may contribute to brain cell death in Alzheimer's dementia. 
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
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
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