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Soy and Senility

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New research suggests eating tofu may make your brain age faster, leading to serious problems with memory and learning in later years.


Even if you never eat tofu -- a custard-like food made from pureed soybeans -- you are still not in the clear. Soy or soybean oil is in everything from salad dressings, mayonnaise, and margarine to breakfast cereals and energy bars, making it the most widely used oil. About 60 percent of all processed foods contain soy protein. And since it is added to cattle and other livestock feed, you may consume it indirectly just by eating your usual steak or hamburger.

Researchers in Hawaii concluded that soy might contribute to brain aging after examining the diets of more than 8,000 men for over 30 years. The more tofu the subjects ate, the more learning and memory problems they suffered in later life. Loss of mental function occurred in 4 percent of the men who ate the least amount of tofu compared with 19 percent of the men who ate the greatest amount of tofu.

These are shocking results for a food touted for its health benefits and recently given FDA approval to make health claims on package labels. Out of 26 foods studied, only tofu was significantly related to brain function. Men who had a high intake of tofu not only scored lower on tests of mental ability, but their brains were more likely to show signs of advanced age and shrinkage.

Although the study was done on men, researchers also interviewed and tested 502 wives of the men in the study -- and came up with similar findings.

The study has created a stir because it contradicts previous research that found soy to be beneficial. Earlier studies have shown soy may fight cancer and heart disease, prevent osteoporosis, and relieve menopause symptoms.

The reason, many experts believe, for the decrease in mental ability, is that soy's isoflavones interfere with enzymes and amino acids in the brain. One of soy's main isoflavones, genistein, limits the enzyme tyrosine kinase in the hippocampus -- the brain's memory center. By interfering with the activity of this enzyme, genistein blocks a process called "long-term potentiation" that is central to learning and memory.

The Hawaiian study was a long-term, well-designed, controlled study, but it was just one study. The results are strong enough to make you sit up and take notice, but only more research can confirm them. If you eat soy, you may want to err on the side of caution. Be sure you know the amount of soy isoflavones you consume each day.

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