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QUESTION: I am concerned about soy and brain aging. I respect your educated experience, follow the A diet, and would extremely appreciate your comments.
ANSWER: Probably the most prominent research that's evoking these suspicions was the published work of Lon White at the Pacific Health Research Institute in Honolulu. Dr. White's ongoing study of 3,734 Hawaiian men over more than thirty years suggests that regular consumption of tofu over many years during their middle age was associated with early dementia or what Dr. White terms "accelerated brain aging." (1)
White's study was a long-range study charting the eating habits of the men since 1965. Final assessments were made of their cognitive functioning (e.g. thinking, learning, memory) along with tests for measuring brain atrophy or shrinkage. The stunning conclusion was that the men who ate two or more servings per week of tofu had steeper declines in brain functioning resulting in dementia.
Yet, despite the dramatic results of his work White recently told an interviewer, "I would be violating a cardinal rule if I said my data says you shouldn't eat tofu [or other soy foods]." While White believes his research is solid, the results, he says, "can't be turned into sweeping conclusions and the findings must be considered only preliminary." In addition this same study concluded that the men who ate tofu had a 65 percent lower incidence of prostate cancer than their anti-soy counterparts.
However, this has not stopped the soy bashers from having a field day.
Dr. White's study was of an observational nature in which the participants chose their lifestyles. He says his findings demand further investigation through more randomized trials. For example, study subjects (humans or animals) would be randomly divided and one group would be fed tofu and the other would not. The incidence of dementia in the two groups would then be measured and compared. A progression of such studies would either confirm or refute Dr. White's findings. He believes it will take at least ten years for a conclusion.
One could argue that if a causal effect existed between soy and Alzheimer's or increased brain aging, a greater incidence of Alzheimer's should exist in Japan and China, where tofu is eaten regularly. Also White's findings have not been duplicated in animal models. Though in general I am not fond of extrapolating conclusions from animal to humans, but in this case it may be well worth noting that since White concluded that the effects of soy isoflavone was on the synthesis of new DNA in the brain, its effects should be more marked in animals, who actually have more brain DNA synthesis active for a longer percentage of their lifespan than humans.
Finally, some researchers are questioning whether the link between tofu and brain aging may actually be another link between aluminum and brain atrophy, since although soy is low in aluminum, it does absorb quite a bit of it when cooked in aluminum cookware. The results of this preliminary investigation suggest that the aluminum concentration in soy products is increased slightly by cooking, particularly in an aluminum pot, and strongly (as much as 15-fold) by some methods of tofu production.
Conclusion: Given the current evidence, soy products should occupy an important place in the blood group A anti-cancer strategy plan.
Many of these concerns prompted the FDA to reject assertions from opponents of soy products attempting to block recommendations for the use of soy to control cholesterol, as was reported in the FDA Register:
"...d. Other. (Comment 20). ….FDA finds that this abstract does not provide a sufficient basis to evaluate the merits and weaknesses of this study. As such, it is not useful in evaluating the safety concerns at issue. Moreover, the report does not provide information on total soy intake or what variables were controlled in the analysis. If tofu or soy were implicated in Alzheimer's disease, its prevalence would be expected to be higher in Japan than in Hawaii, but White et al. (Ref. 115) found the prevalence of Alzheimer's disease was higher in Hawaii than in Japan. Therefore, FDA is not persuaded by the comment raising concerns about potential adverse effects of soy protein in dementia and brain atrophy in older persons.
1. White LR, Petrovitch H, Ross GW, Masaki K, Hardman J, Nelson J, Davis D, Markesbery W. Brain aging and midlife tofu consumption. J Am Coll Nutr. 2000 Apr;19(2):242-55.