I wonder if you could answer an important question for me: My wife and I practically live on Soy and Tofu. We have tofu at least three times a week, and drink soy milk every day. Lately at least five friends have said to me that there seems to be evidence that soy products can contribute to dementia. Since I have minor memory problems, and my wife seems to be having them too (though breastfeeding a two-year-old most of the night can definitely contribute!) we began to wonder if there is any truth to these rumors. I am sure you have looked into them and can give me your opinion, or tell me where to get to find out more. Would much appreciate it.
Thanks for your question. The health benefits of soy products have been well established. But your friends, and now you, have felt the reverberations from a surprising study that was published in April 2000, in the Journal of the American College of Nutrition.
The study, conducted in Hawaii by Lon White, M.D., and his associates, was part of the Honolulu Heart Study. Looking at the diets and the risk of dementia of Japanese men residing in Hawaii, the study found that men who ate the most tofu during their mid-40s to mid-60s were more likely to have dementia and Alzheimer’s as they grew older.
The correlation between tofu and cognitive decline was strong, and could not be explained by confounding factors like age, education, and obesity. In this study, men who had eaten two or more servings of tofu per week in midlife were 2.4 times as likely as men who rarely or never ate tofu to become senile or forgetful by old age. Even the wives of men who ate tofu showed more signs of dementia. White and the other researchers said the brains of the tofu-eaters seemed to have aged more rapidly. By the time the men reached their 80s and 90s, the tofu-eater’s brains seemed to be the equivalent of non-tofu eater’s brains that were five years older.
Scary stuff for soy eaters. And if that’s all you knew, it would look pretty bad for people like you (and me) who have been eating lots of soy for some time.
But that’s not all we know. We know, for example, that dementia rates are lower in Asian countries (where soy intake is high) than in western countries. We know that the Japanese lifestyle (with its high soy intake) has long been associated with longer life span and better cognition in old age. And we know that Seventh Day Adventists, many of whom consume soyfoods their whole lives, have less dementia in old age than the general population.
The Honolulu Heart Study is far indeed from conclusive. It measured intake of only 27 foods, and there are many lifestyle factors for which it did not control. Researchers acknowledged that tofu consumption might be a marker for some other factor that affects cognitive function. And this would make tofu an innocent bystander. Results of other studies, say soy researchers Mark and Virginia Messina, “would suggest this is true.”
A number of clinical studies have shown that soy and isoflavones from soy are actually beneficial for cognition. In one study, published in the journal Psychopharmacology in 2001, young adult men and women who ate a high-soy diet experienced substantial improvements in short-term and long-term memory and in mental flexibility. Other studies have found that isoflavone supplements from soy improve cognitive function in postmenopausal women.
It is important to bear in mind that the Honolulu Heart Study is the only study that has suggested a link between tofu consumption and dementia in old age. Having studied the literature, soy researchers Mark and Virginia Messina conclude that “there is no reason to believe that eating soyfoods is harmful to brain aging.”
I agree, which is why members of my household happily eat tofu two or three times a week, soy milk daily, and tempeh once or twice a week.
Is there anything else you can do to protect your brain functioning as you age? Absolutely.
- Regular exercise and having an active mental life are both associated with better cognitive aging.
- If you are addicted to alcohol, tobacco, and/or drugs, you now have yet another reason to overcome this problem, because over time these vices take a dramatic toll on the brain.
- Minimize your exposure to toxic chemicals, including heavy metals like lead, aluminum and mercury.
- Don’t take prescription drugs unnecessarily. Serious memory problems have been associated with cholesterol-lowering statin drugs.
- And don’t take over-the-counter drugs lightly, either. Even seemingly harmless medications, such as antihistamines and decongestants, can pose unexpected risks.
Can supplements help? Taken selectively, yes. The B-vitamins have been shown to be particularly useful, especially for older people. Elderly people are more likely to have B-vitamin deficiencies than younger people, due to greater use of prescription drugs, and lower vitamin bioavailability due to declining levels of the enzymes involved in vitamin metabolism. Of the B-vitamins, choline is specifically critical for the preservation of memory. As well, blood-flow enhancers like quercetin and d-phenylalinine, and herbals such as Huperzine, Rhodiola rosea, and gingko have been shown to improve memory and focus in older people.
But most important of all is the food you eat.
Eating a diet high in antioxidants is essential. Antioxidants protect against free radical damage, and free radical damage is deeply implicated in the development of cognitive dysfunction and dementia.
The extent to which free radicals can damage our brains is dependent on whether we get enough antioxidant shields to protect ourselves from them. Vegetarians have an advantage here, because plant foods contain more antioxidants, and animal-based foods tend to activate free radical production and cell damage.
As I mentioned, there is only a single study that suggests soy might be a problem. On the other hand, there are a great many studies that demonstrate the benefit of a plant-based diet high in antioxidants for brain function.
I’ll briefly mention just a few of these.
- A study published in the American Journal of Epidemiology found high vitamin E and vitamin C levels to each be associated with less memory loss in the elderly.
- A study published in 1997 in the American Journal of Clinical Nutrition examined dietary intake and cognitive function in a large group of people aged 65 to 90 years. Researchers concluded that “a diet with less fat, saturated fat, and cholesterol, and more carbohydrate, fiber, vitamins (especially folate, vitamins C and E, and beta-carotenes), and minerals (iron and zinc)…(was shown) not only to improve the general health of the elderly but also to improve cognitive function.”
- A study published in 1997 in the Journal of the American Geriatric Society found that scores on mental tests were higher among older people who consumed the most vitamin C and beta-carotene.
- Other studies published in the British Medical Journal and the Journal of the American Medical Association have found that low levels of vitamin C in the blood are linked to poorer cognitive performance in old age, while B vitamins and beta-carotene are linked to better cognitive function.
While only one study has suggested a link between soy consumption and cognitive dysfunction, many studies have found distinct correlations between dietary antioxidants and improved cognition. This is quite important. And by the way, I know of no study that suggests that consuming more dietary antioxidants impairs mental functioning or increases memory loss.
The best sources of dietary antioxidants are fresh vegetables and fruits, whole grains and legumes. It is clear that a diet rich in these foods provides significant protection against cognitive decline.
A whole foods plant-based diet based on fresh vegetables and fruits, whole grains and legumes is good for brain function because it is rich in antioxidants, but there’s another reason, too. The health of your arteries and vessels that transport blood to and from your brain is dependent on how well you eat. Diets high in saturated fats and trans-fats reduce the flow of oxygen and nutrients to your brain, and pave the way for strokes to occur. On the other hand, diets that maintain healthy cholesterol levels and a healthy cardiovascular system ensure proper blood flow to the brain, supplying the necessary raw ingredients for it to function optimally.
Many studies speak to us about the relationship between diet and the most serious forms of dementia, such as strokes (vascular dementia) and Alzheimer’s. Here are a few:
- Studies published in the Journal of Alzheimer’s disease and the Journal of the American Medical Association compared Alzheimer’s rates to dietary variables in 11 different countries, and found the highest rates of the disease among people with a high fat intake and low intake of whole grains.
- In a publication from the famous Framingham study, researchers concluded that for every three additional servings of fruits and vegetables a day, the risk of stroke is reduced by 22 percent. And three servings, as defined by this study, are not very much. In this study, 1/2 cup of peaches, of 1/4 cup of tomato sauce, or 1/2 cup of broccoli, or one potato were each considered one serving. By this standard, the men in the study who consumed the most fruits and vegetables consumed as many as 19 servings a day.
- In yet another study, scientists analyzed food intake and cognitive performance for over 5,000 older people. Publishing their results in 1997 in the Annals of Neurology, they found that people who consumed the most fat and saturated fat had the highest risk of dementia due to vascular problems.
- A large study published in the Archives of Neurology in 2003 found that older people can reduce their risk of developing Alzheimer’s disease by eating fish, consuming fish oil, or taking DHA supplements. Participants in the study who consumed fish once a week had a 60% lower risk of developing the disease than did those who rarely or never ate fish. Participants whose daily intake of DHA was about 100 mg/day had an incidence of Alzheimer’s which was 70% lower than those with an intake of 30 mg/day or less.
- Another study on Alzheimer’s disease found that the risk of getting the disease was 3.3 times greater among people whose blood folic acid levels were in the lowest one-third range, and 4.5 times greater when blood homocysteine levels were in the highest one-third. The study found it desirable to maintain low blood homocysteine levels and high blood folic acid levels, a situation most easily achieved on a whole foods plant-based diet with ample vitamin B-12. (Because adequate B-12 is necessary to regulate homocysteine levels, people whose B-12 levels are low may risk higher homocysteine.) The best source of folic acid is green leafy vegetables. Homocysteine is an amino acid that is derived primarily from animal protein.
In our society, we come to take for granted that aging will bring restricted short term memory and diminished mental faculties. A visit to most nursing homes demonstrates how commonly and how markedly people in our society experience cognitive decline as they age. As one comedian described it, “First you forget names, then you forget faces, then you forget to pull your zipper up, then you forget to pull your zipper down.”
But there is good science to show that we can experience clear thinking well into our later years. It is not soy consumption, but the standard American high-saturated fat diet, low in vegetables and fruits and whole grains and thus low in brain-preserving antioxidants, that is primarily responsible for the unhealthy outcomes we see so often in our elderly.
By the way, you mentioned that your wife is now breast-feeding a two-year-old. Congratulations to you both on your new child, and doubly congratulations to your wife for breastfeeding for so long. The health benefits for breastfeeding are dramatic.
Keep on laughing, keep on taking care of yourself, and you won’t be one of the people who ends up lamenting, “If I knew I was going to live this long, I would have taken better care of myself.”
With joy in the adventure of life,