By John MacArthur
"Tofu Shrinks Brain!" No science fiction scenario, this sobering soybean revelation is for real. But how did the "poster bean" of the ’90s go wrong? Apparently, in many ways--none of which bode well for the brain.
In a major ongoing study involving 3,734 elderly Japanese-American
men, those who ate the most tofu during midlife had up to 2.4 times the risk of later developing Alzheimer’s disease. As part of the three-decade long Honolulu-Asia Aging Study, 27 foods and drinks were correlated with participants’ health. Men who consumed tofu at least twice weekly had more cognitive impairment than those who rarely or never ate the soybean curd.1, 2
"The test results were about equivalent to what they would have been if they were five years older," said lead researcher Dr. Lon R. White from the Hawaii Center for Health Research. For the guys who ate no tofu, however, they tested as though they were five years younger.
What’s more, higher midlife tofu consumption was also associated with low brain weight. Brain atrophy was assessed in 574 men using MRI results and in 290 men using autopsy information. Shrinkage occurs naturally with age, but for the men who had consumed more tofu, White said "their brains seemed to be showing an exaggeration of the usual patterns we see in aging."
Phytoestrogens--Soy Self Defense
Tofu and other soybean foods contain isoflavones, three-ringed molecules bearing a structural resemblance to mammalian steroidal hormones. White and his fellow researchers speculate that soy’s estrogen-like compounds (phytoestrogens) might compete with the body’s natural estrogens for estrogen receptors in brain cells.
Plants have evolved many different strategies to protect themselves from predators. Some have thorns or spines, while others smell bad, taste bad, or poison animals that eat them. Some plants took a different route, using birth control as a way to counter the critters who were wont to munch.
Plants such as soy are making oral contraceptives to defend themselves, says Claude Hughes, Ph.D., a neuroendocrinologist at Cedars-Sinai Medical Center. They evolved compounds that mimic natural estrogen. These phytoestrogens can interfere with the mammalian hormones involved in reproduction and growth--a strategy to reduce the number and size of predators.
Toxicologists Concerned About Soy’s Health Risks
The soy industry says that White’s study only shows an association between tofu consumption and brain aging, but does not prove cause and effect. On the other hand, soy experts at the National Center for Toxicological Research, Daniel Sheehan, Ph.D., and Daniel Doerge, Ph.D., consider this tofu study very important. "It is one of the more robust, well-designed prospective epidemiological studies generally available. . . We rarely have such power in human studies, as well as a potential mechanism."
In a 1999 letter to the FDA (and on the ABC News program 20/20), the two toxicologists expressed their opposition to the agency’s health claims for soy, saying the Honolulu study "provides evidence that soy (tofu) phytoestrogens cause vascular dementia. Given that estrogens are important for maintenance of brain function in women; that the male brain contains aromatase, the enzyme that converts testosterone to estradiol; and that isoflavones inhibit this enzymatic activity, there is a mechanistic basis for the human findings." 3
Although estrogen’s role in the central nervous system is not well understood, White notes that "a growing body of information suggests that estrogens may be needed for optimal repair and replacement of neural structures eroded with aging."
One link to the puzzle may involve calcium-binding proteins, which are associated with protection against neurodegenerative diseases. In recent animal studies at Brigham Young University’s Neuroscience Center, researchers found that consumption of phytoestrogens via a soy diet for a relatively short interval can significantly elevate phytoestrogen levels in the brain and decrease brain calcium-binding proteins.4
Concerns About Giving Soy to Infants
The most serious problem with soy may be its use in infant formulas. "The amount of phytoestrogens that are in a day’s worth of soy infant formula equals 5 birth control pills," says Mike Fitzpatrick, a New Zealand toxicologist. Fitzpatrick and other scientists believe that infant exposure to high amounts of phytoestrogens is associated with early puberty in girls and retarded physical maturation in boys.5
A study reported in The Lancet found that the "daily exposure of infants to isoflavones in soy infant-formulas is 6-11 fold higher on a bodyweight basis than the dose that has hormonal effects in adults consuming soy foods." (This dose, equivalent to two glasses of soy milk per day, was enough to change menstrual patterns in women.6 In the blood of infants tested, concentrations of isoflavones were 13,000-22,000 times higher than natural estrogen concentrations in early life.7 )
From Matt Rosenberg,
much more on soy and it’s affects at this link
http://www.westonaprice.org/soy/soyandbrain.html
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