Too much tofu
induces brain aging,
A Hawaii research team saysBy Helen Altonn
high consumption of the soy product
by a group of men lowered
Tofu is touted for its health benefits, but also may pose health risks, says a Hawaii scientist.
A Hawaii study shows a significant statistical relationship between two or more servings of tofu a week and "accelerated brain aging" and even an association with Alzheimer's disease, says Dr. Lon White.
The Pacific Health Research Institute researcher urged caution at a recent conference in Washington as scientists from around the world discussed the role of soy products in the prevention and treatment of disease.
The symposium was sponsored by giant soybean growing and processing firms such as Archer Daniels Midland and DuPont.
The largely unregulated food supplements industry is preparing to step up sales, claiming that isoflavones, plant chemicals found in high concentrations in soybeans, offer "natural" cures for breast cancer, osteoporosis, prostate cancer, heart disease, menopausal "hot flashes" and other chronic conditions.
Negative conclusionsBut, White said in an interview, "The majority of scientists said the data they were talking about for beneficial effects on health is very weak" and doesn't really support health claims for soy foods.
White and his associates have been studying diseases and aging in a group of Japanese-American men who volunteered for medical research in 1965. The Honolulu Heart Program began with 8,006 men born from 1900 through 1919. They were identified through World War II Selective Service registration records.
In comparing the dietary habits and health of the Japanese-American men in the study group between 1965 and 1993, White said the scientists found "a significant link between tofu consumption during midlife and loss of mental ability and even loss of brain weight."
The men were questioned about 27 foods and drinks, with data showing that those who ate more tofu were apt to have impaired mental ability, White said. Tofu was the only consistent link among the men, he said. The rate of brain impairment, which normally increases with age, also went up faster in the men who ate the most tofu, he said.
"The test results were about equivalent to what they would have been if they were five years older," he said. "Guys who ate none, their test scores were as though they were five years younger."
The brains of 300 men who died also were examined in a unique autopsy study conducted as part of the Honolulu aging project, White said. The 300 men didn't appear to have had any more strokes than the average person, and their blood vessels didn't look different.
"But what I did see was (that) the simple weight of the brain was lower," he said. Shrinkage occurs naturally with age, but atrophy progressed more rapidly in those men who had consumed more tofu, White said.
He said the wives of about 500 men also provided information about what they ate, and the findings correlated with what their husbands said.
Stark contrastSo the scientists obtained four independent indicators of an adverse effect from frequent eating of tofu and changes in the brain with aging, White said.
Those who ate a lot of tofu, by the time they were 75 or 80 looked five years older, he said.
"Why in the world would that happen?" he said. "Everyone knows protein in tofu and soy is wonderfully nutritious. Everyone knows fats are wonderfully nutritious.
"But more and more and more over the last five to 10 years, people have been claiming the health benefits of soy foods are less related to its nutrient composition, proteins and fat, and more related to other molecules that occur in tofu made by soy plants and act as pharmacological agents."
Isoflavones, the most talked about, "are molecules that the soy plant makes while it's germinating to help it fend off mold and other things that attack the plant in the ground," White said.
They're plant molecules that look like estrogens but they're not natural estrogens, he said. "When they get into cells, they actually affect the metabolism of cells. They inhabit certain kinds of enzymes and alter (the) metabolism of cells.
"The bottom line," stressed White, "is these are not nutrients. They are drugs. They will have some benefits and some negative things."
Groundbreaking workWhite said his study, to his knowledge, is the only one to show strong evidence of serious adverse effects from a soy product. His group is seeking a new National Institutes of Health grant to continue research on the effects of tofu.
It may be beneficial for heart disease and bones, White said. "We don't know. All we know, in our study, is there appears to be an adverse relationship."
Among those at the conference was Finnish scientist Herman Adlercreutz, who became interested in soy after observing that breast cancer and colon cancer were less common in Japan than in Finland. His studies 20 years ago led to a scientific explosion of interest in soy and its components.
Adlercreutz believes more dietary soy, a staple of Asian diets, would improve the health of Americans and people of other Western countries. But he said at the conference, "I am myself frightened a little bit by all of this. There is so much we don't know."
Mark Messina, a soy foods expert and former researcher with the Diet and Cancer Branch of the National Cancer Institute, told the scientists, "It's simply not possible as yet to draw any conclusions about soy consumption and cancer prevention, but further research is certainly warranted."
Companies that make money from soy products are pushing hard to have people think of them as "perfect food," White said
"But if we're talking about soy foods containing substances that have effects on health that aren't nutrients, that are not vitamins, or fat, but change how cells operate, they're acting as drugs act. And the way we think of them should be how we think about drugs."