What's the latest on Soy?
Kenneth Setchell, Professor of Pediatrics at the Children’s Hospital Medical Center and University of Cincinnati, USA, is credited with the discovery of the first mammalian dietary oestrogens and the proposal that they convey health benefits. He is recognised as one of the foremost authorities on phytoestrogens in the world.
Professor Setchell is also co-author of Eat to Live—A phytoprotection plan for life. This easy-to-read, easy-to-understand book explains the “why to” and “how to” of adding more phytoestrogen-rich foods to your diet for a long-term health benefit. Here’s what he told Sanitarium’s Nutrition Service in a recent interview.
We know that soy foods are nutritious, but what is it about soy that makes it so important in our diets?
Well, soy contains an extremely high quality protein. In fact, it matches up very well, if not better, to animal protein, in terms of its overall quality.
I feel that this is not generally recognised by the public, who tend to perceive soy protein as being an inferior protein.
As a vegetable protein, soy is important for a number of reasons:
It has no cholesterol—and that is an important factor in terms of treating people who have high cholesterol levels, which is a large proportion of the adult population.
As a food, it is low in saturated fat, which is beneficial in maintaining healthy cholesterol levels and therefore helping to reduce the risk of heart disease.
Soy is high in fibre and carbohydrates. In fact, there is new research to suggest the favourable carbohydrate profile may be useful in the treatment of diabetes.
Soy contains a large number of other important micronutrients. Some of these are what we generally refer to as phytoprotectants. The one class that interests me most is the group of natural plant oestrogens (phytoestrogens) called isoflavones, which are proving to have important effects in the body.
What are the main health benefits of consuming soy?
Probably one of the most accepted health effects of soy consumption is the benefit of soy protein to reduce the risk for heart disease by lowering blood cholesterol.
In addition, a number of studies are now showing that the isoflavones in soy appear to have some very beneficial effects on blood vessels. The isoflavones appear to improve the flexibility of blood vessels so that they respond more easily to changes in pressure, which is likely to reduce the risk for stroke and heart disease.
I think there is good evidence that consuming soy protein is likely to be beneficial in the long term in preventing bone loss, because it tends to reduce calcium loss from bone.
In the area of menopause, soy has been touted as a possible alternative to hormone replacement therapy (HRT). The data is somewhat mixed but overall the evidence suggests that there is a benefit to women who are suffering hot flushes, particularly for those who have a more severe incidence of hot flushes. Not all women will experience relief from hot flushes, possibly because of how people metabolise the phytoestrogens in soy. And soy will not have the equivalent effect of reducing or alleviating the symptoms of menopause that HRT will give, but then it doesn’t have the side effects of HRT.
The other big area of interest is the use of soy in reducing the risk of cancer. At present, there is a lot of very strong data from animal models of cancer and test-tube studies of human cancer cells showing that soy isoflavones stop the growth of tumour cells, and prevent or slow the progression of tumour growth. However, at this point in time we really don’t have any solid data from long-term clinical studies of using soy for cancer prevention in humans. There is some evidence that soy may be beneficial to men in reducing the risk of prostate cancer, more so than for reducing the risk of breast cancer in women.
What we do know is that the incidence rates for cancer in countries that consume soy on a daily basis is extremely low compared to the Western world. Now, whether that means that soy is protective or not, or whether there are some other lifestyle factors associated with people who consume soy, we really don’t know.
There is, however, no evidence to suggest that healthy people who consume soy regularly are at increased risk of cancer. By contrast, there is certainly evidence that there is a decreased risk of cancer and this may be particularly the case the earlier in life one begins to eat soy foods regularly.
So, how much soy should we eat to gain some health benefit, and how do you suggest we do this?
Well, I could base my recommendation on the health claims in America and Britain. These claims are based on the principle that if you consume 25 grams of soy protein a day, there will be the health benefits of reducing your risk of heart disease.
However, I do not believe this amount to be necessary, as the reality is that the Japanese do not consume 25 grams of soy protein per day. Their average consumption is nearer to six-to-eight grams of soy protein, and that is consumed lifelong, almost on a daily basis.
In fact, if you look at both China and Japan, on average, their adults have relatively low blood cholesterol levels compared to Western countries. Interestingly, the studies out of Japan show that the more soy they consume, the lower their cholesterol.
Based on this information, my personal recommendation is that it should be adequate for us to consume 6-8 grams of soy protein per day to confer some long-term benefits in terms of helping to improve your cholesterol levels and for general health benefits. This would probably be about one to two servings of soy food each day. The advantage is that if you consume these soy foods, you will probably also be replacing other less healthy foods that we eat too much of in the Western world.
What would you recommend to women who may be looking for help to manage menopausal symptoms?
Well, that is a difficult question to answer. I don’t think there is any strong evidence to help us know how much soy you should eat to help relieve menopausal symptoms. I would say one to two servings may be beneficial. It is very difficult to know because with that population group it is the isoflavones that are likely helpful and the amount in soy foods vary greatly.
If people don’t like the taste of soy foods, can they take a supplement to get the same benefits?
This is a difficult question to answer, as first, a supplement is not going to give you significant amounts of soy protein. We need to keep in mind that many of the studies showing cholesterol-lowering benefits and reduced risk of heart disease were based on consuming 25 grams of soy protein per day.
However, a supplement is going to give you an extract of soy that contains many of the micronutrients, including isoflavones, and most supplements will deliver amounts of isoflavones that you would typically get in a soy meal—and maybe even higher amounts.
We do not yet know whether it is important that the isoflavones are present naturally in the soy food to maximise their effect, but I would not denigrate supplements because they may show benefits in some people.
The concern with supplements is that you really have no control over the quantity people will consume. As isoflavones in supplements are bioactive substances, if taken in large quantities there is always the possibility of negative effects. Over-consumption of isoflavones would be difficult when eating soy foods.
Overall, you are unlikely to get the complete benefits of a soy food from a soy supplement because, in addition to the micronutrients, there are the other components in soy that equally contribute to the overall healthfulness of the food.
What are the new areas of soy research that we will likely hear
about in the future?
There is so much research on soy going on worldwide, particularly on the isoflavones but also other components of soy such as the fatty acid composition and the proteins. If I had to predict some areas that are likely to emerge, I would say:
We are likely to see new data on the effects of soy on the brain. Hopefully this will reinforce some of the small studies that have shown that consuming soy protein/foods seems to have a beneficial effect on cognition, on improving learning skills and also on anxiety.
A second area that we can look out for in the next year or so will be the use of soy in trying to manage diabetes and obesity.
Bone will continue to be something of interest, in terms of the benefit of soy and isoflavones in preventing osteoporosis. Our own recently published study showed that consuming as little as two glasses of soymilk per day over a two-year period, prevented bone loss in a group of postmenopausal women.
Research into soy and cancer will also continue. There is still considerable concern about the issue of breast cancer, particularly for women who are in the high-risk group. In the next few years I think we will see studies that might address the issue of whether such women should eat soy protein because there are many recommendations being made by doctors, that these women should not consume soy protein. However there is no clinical evidence to support these recommendations. They are based on the known increased risk that oestrogens have for breast cancer and the association of soy foods with phytoestrogens. However, there really is no clinical evidence that soy is detrimental to women who have breast cancer. I don’t believe soy to be detrimental for women who have breast cancer, but there needs to be more research to prove that. I think that we may also start to see some data emerge on the beneficial effects of soy and isoflavones in soy on reducing the risk for prostate cancer.
The other area that I think is new, is the area of skin. We know oestrogens are very beneficial to the skin. There is a lot of interest in whether soy, and the isoflavones, can be helpful in improving the quality of skin as people age or preventing the deterioration in skin, particularly the loss of collagen that causes wrinkling.
Soy infant formulas is another area that continues to be studied. Whether soy infant formulas are good or not, surprisingly continues to be a contentious issue and it is one that will ultimately be difficult to resolve because it will require extremely long-term and expensive studies. Therefore, we may start to see more short-term studies on soy infant formula. I would think they would be likely to show that soy infant formula, rather than being negative in the long term for infants, is likely to be beneficial.
| This is an extract from July 2005
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