Tofu 'may raise risk of dementia'
Eating high levels of some soy products - including tofu - may raise the risk of memory loss, research suggests.
The study focused on 719 elderly Indonesians living in urban and rural regions of Java.
The researchers found high tofu consumption - at least once a day - was associated with worse memory, particularly among the over-68s.
The Loughborough University-led study features in the journal Dementias and Geriatric Cognitive Disorders.
Soy products are a major alternative protein source to meat for many people in the developing world.
But soy consumption is also on the increase in the west, where it is often promoted as a "superfood".
Soy products are rich in micronutrients called phytoestrogens, which mimic the impact of the female sex hormone oestrogen.
There is some evidence that they may protect the brains of younger and middle-aged people from damage - but their effect on the ageing brain is less clear.
The latest study suggests phytoestrogens - in high quantity - may actually heighten the risk of dementia.
Lead researcher Professor Eef Hogervorst said previous research had linked oestrogen therapy to a doubling of dementia risk in the over-65s. She said oestrogens - and probably phytoestrogens - tended to promote growth among cells, not necessarily a good thing in the ageing brain.
Alternatively, high doses of oestrogens might promote the damage caused to cells by particles known as free radicals.
A third theory is that damage is caused not by the tofu, but by formaldehyde, which is sometimes used in Indonesia as a preservative.
The researchers admit that more research is required to ascertain whether the same effects are found in other ethnic groups.
However, previous research has also linked high tofu consumption to an increased risk of dementia in older Japanese American men.
Fermented product
Professor David Smith, of the University of Oxford, said tofu was a complex food with many ingredients which might have an impact.
However, he said: "There seems to be something happening in the brain as we age which makes it react to oestrogens in the opposite way to what we would expect."
The latest study also found that eating tempe, a fermented soy product made from the whole soy bean, was associated with better memory.
Professor Hogervorst said the beneficial effect of tempe might be related to the fact that it contains high levels of the vitamin folate, which is known to reduce dementia risk.
"It may be that that the interaction between high levels of both folate and phytoestrogens protects against cognitive impairment."
She also stressed that there was no suggestion that eating tofu in moderation posed a problem.
Rebecca Wood, of the Alzheimer's Research Trust, which funded the study, said more research was needed to pin down the potential risks and benefits of so-called superfoods.
However, she said: "This kind of research into the causes of Alzheimer's could lead scientists to new ways of preventing this devastating disease.
"As over half a million people have Alzheimer's in the UK today, there is a desperate need to find a new prevention or cure."
Story from BBC News 4 April 2008.
Commentary
This is one of the worst articles I have ever read on the subject.
Phytooestrogens are not oestrogens. The term Phytooestrogen is from phyto, meaning plant and oestrogen (or estrogen in North America) meaning oestrogen like in action. However phytooestrogens are different to human oestrogens or xeno-oestrogens (environmental oestrogens often from the breakdown of petro-chemicals etc).
Naturally occurring oestrogens in the human body can function in both a positive and negative way. On the one hand certain types of oestrogen can increase the risk of some cancers, yet others may be cardio protective. The following blanket claims in the article are perplexing:
She said oestrogens - and probably phytooestrogens - tended to promote growth among cells, not necessarily a good thing in the ageing brain.
Alternatively, high doses of oestrogens might promote the damage caused to cells by particles known as free radicals.
Firstly the researcher is applying the “all oestrogens are the same rule” to phytooestrogens which is largely conjecture and not born out by rigorous research. Secondly while high doses of human or xenooestrogens may in some cases cause free radical damage this has not been proven of phytooestrogens.
While phytooestrogens may weakly influence oestrogen activity in the body, most of the negative press that they get comes from scientists extrapolating that if an oestrogen is capable of a negative function in the body than anything with oestrogen in the name will do the same. However phytooestrogens, in their natural state, are present in almost every “health food” including most nuts, seeds, grains and legumes. Perhaps where tofu (and soy milk) differs is that the refining process removes all the fibre from the plant that may alter the way these naturally occurring chemicals are metabolized. Yet the article makes no distinction between the food product (tofu) and phytooestrogens - a diverse group of plant constituents, in the claims that is makes.
Despite the endline "that there was no suggestion that eating tofu in moderation posed a problem", this report went to press with a blaring headline that implied that tofu causes dementia. Furthermore, many of the questions raised in the actual text of the report, that may disprove the inferred negative effects of phytooestrogens, are left hanging. Significantly, there is the issue of possible formaldehyde (a know carcinogen) contamination in the Javanese tofu. The production of this product significantly differs from the tofu available in countries like Australia. Formaldehyde is a rogue chemical with a proven track record of doing damage to the human body. Also buried in the story is news of the benefits of another soy product - tempe (tempeh). This phytooestrogen containing food appears to have the opposite effect on the brain. The same story could have legitimately carried the tagline that “Phytooestrogens reduce the risk of dementia”.
While the report mentions that a deficiency in folic acid (folate) may promote dementia and that tempeh contains folate, there is a lot more that could be said on this subject. Folic acid is primarily derived from plant foods. A deficiency in this nutrient has been shown to triple the risk of dementia in the elderly.
The majority of people in the Western world who suffer from dementia have never eaten tofu or been regular tofu consumers. The growing risk appears to be a lack of folate (possibly due to its relationship with homocysteine), which is from plant foods that coincidentally mostly contain phytooestrogens.
But should we eat huge slabs of tofu every day? I don’t think so – just as I wouldn’t recommend a large daily intake of dairy, meat, eggs or any processed food. When a diet is rich in animal products or refined foods it is usually eaten at the expense of fruits and vegetables. Traditionally tofu is eaten in small amounts; think of the little cubes of bean curd in a bowl of Japanese miso soup. Tofu (and soymilk) differs from soybeans and tempeh due to being refined. Processed foods can never be the cornerstone of a health promoting diet.
More on the soy controversy in this Health Trip article.
No comments:
Post a Comment