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Eating Well
Tofu and Brain Aging

Men who ate the most tofu during their mid-40s to mid-60s showed the most signs of mental deterioration in their mid-70s to early 90s. The consumption of tofu two or more times per week was detrimental to brain function, according to a study published in the April issue of the Journal of the American College of Nutrition.

This finding will send up a red flag for American men who are eating tofu and taking soy supplements for the sake of their prostates. Fresh evidence is coming out of US laboratories to show that soy isoflavones have potent effects and "may inhibit prostate tumor growth via direct activation of intracellular signaling cascades leading to apoptosis."

The new tofu study finds that poor cognitive test performance, and two measures of brain atrophy or shrinkage were associated with higher midlife tofu consumption among men. The cognitive tests measure attention, concentration, memory, judgement and several other indicators of brain function.

This analysis is part of the Honolulu Heart Program which began tracking the health of 8,000 Japanese-American men in 1965. Tests of cognitive function were administered to 3734 men; brain images were obtained from 574 and autopsy results were available for 290 to evaluate brain atrophy. In addition, test scores of 502 wives of participants were also analyzed.

The more tofu eaten, the greater the likelihood of mental decline according to Lon White, MD, of the Hawaii Center for Health Research and lead author of the study. Dr. White said that both men and women eating the most tofu were up to twice as likely to show some signs of impaired mental function later in life than those who rarely ate tofu.

The proposed link between tofu consumption and decline of brain function is the isoflavones now being touted for prevention of prostate cancer and breast cancer. These chemicals which have a mild estrogenic effect also affect an enzyme in the body, tyrosine kinase, which may block changes in the brain related to learning. Hundreds of laboratory studies have found that isoflavones directly inhibit the growth of different types of cancer cells.

Recently, soybean isoflavones were found to markedly inhibit prostate tumors in mice implanted with prostate cancer cells. Other research indicates isoflavones are concentrated in prostate tissue, providing further support for the notion that soyfoods may reduce prostate cancer risk.

 In an editorial accompanying the research article, Dr. Francine Grodstein of Harvard Medical School wrote that this first demonstration of a relationship between tofu consumption and decline in brain function should be the catalyst for more research. Grodstein and colleagues pointed out several limitations of measuring diet and brain function and structure, all of which change over time. Because we know so little about a possible connection between diet and cognitive decline, this type of research should be given high priority since the elderly portion of the population is expanding rapidly.

Men commonly report that hormonal therapy for prostate cancer has a negative impact on cognition and memory. If eating tofu, or taking genistein pills, against prostate cancer or its recurrence gradually fogs the brain, it becomes less attractive as a "natural" remedy and more like a drug with specific positive effects and some unfortunate negative side effects.

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Two findings about potent effect of soy for prostate cancer were presented at poster sessions at the American Association for Cancer Research Conference in San Francisco April 2-4:

"The involvement of caspase-3, bcl-2, and bax in soy isoflavone (genistein)-induced apoptosis in human prostate cancer cells. Yanping Guo, Steven K Clinton, The Ohio State Univ Coll of Medicine and Public Health, Columbus, OH. and Identification of Genes Differentially Regulated by Genistein in Human Prostate Cancer LNCaP Cells Using cDNA Microarray Screening V. G. Samedi, L. Rice, T. A Medrano, K. T Shiverick, Univ of Florida, Gainesville, FL.