Although soyfoods are widely recognise for their nutritional qualities, interest in soyfoods has risen recently because scientists have discovered that a soy component called isoflavones appears to reduce the risk of cancer.
More research needs to be done to determine exactly how isoflavones work, but it appears that as little as one serving of soyfoods a day may be enough to obtain the benefits of this anticancer phytochemical.
Scientists have compiled a database that gives values for the major isoflavones in 128 soyfoods and ingredients. It is important, though, to understand the entire nutritional value of specific soyfoods so that dietetic decisions can be made. For instance, soy protein has been found to be effective in reducing cholesterol, in treating kidney disease, and may cause calcium to be better utilised, helping to ward off osteoporosis. Some soyfoods such as miso contain high amounts of sodium, and should be avoided by people who need to minimise their sodium intake. A single serving of tempeh contains twice as much fibre as the average American eats in a day.
Isoflavones: you have read any health and nutrition columns in consumer magazines, newspapers or the internet, you are aware of the terms isoflavone, phytoestrogen and phytochemical. At times it may seem a little confusing.
Besides, aren't the nutrients we've known about for years adequate for our health and well-being? No one questions the importance of protein, carbohydrates, fat, vitamins and minerals to our health; however, new frontiers in the field of nutrition will be explored as we learn more about specific phytochemicals such as isoflavones. Phytochemicals are non-nutritive, meaning they are neither vitamins nor minerals. There are many hundreds of these bioactive plant chemicals found in dietary sources of fruits, vegetables, legumes, whole grains, nuts, seeds, herbs and spices. Isoflavones have received a great deal of research, especially for possible cancer and heart disease-preventive properties.
To date, most of the research has been done in animals, cell culture and in vitro studies. Isoflavones are a type of phytoestrogen, compounds that have weak estrogenic activity. There are many types of phytoestrogens and not all are in edible plants. Isoflavones are found in chick peas and legumes. The legume, soy, has the most concentrated amount.
The following questions are commonly asked by consumers trying to learn more about isoflavones.
Q. Where are isoflavones found in the soybean?
A. The isoflavones seem to be concentrated in the soybean hypocotyl (the part of the seedling below the seed leaves) with low to moderate amounts in the cotyledon (first layer of leaves formed on seedling).
Q. Are there factors which make a difference in the amount and forms of isoflavones in the soybean?
A. Soybeans contain three types of isoflavones in four chemical structures. Exact chemical analysis done on a wide variety of soyfoods and ingredients has shown a great difference in amounts of the isoflavones as well as their chemical forms. The variety of soybean grown, growing conditions, location and crop year, can all make a difference in the amount of isoflavones in soybeans.
Q. What soyfoods have the greatest amount of isoflavones?
A. All the soyfoods in the following list are excellent sources of isoflavones, providing a range of 30 - 50 milligrams per serving.
Roasted soy nuts (1 ounce)
Soy flour (1/2 cup)
Soy grits (1/4 cup)
Textured soy protein (1/2 cup, cooked)
Yellow, green vegetable or black soybeans (1/2 cup, cooked)
Regular soymilk (1 cup)
Tempeh (1/2 cup)
Tofu (1/2 cup)
Q. Don't other soyfoods or soy ingredients contain isoflavones?
A. Yes, most do, just in significantly smaller quantities. For example, miso is a good source, but who eats a 1/2 cup of miso, since it is used as an ingredient? Soy hot dogs, soy burgers, soy cheeses, soy yogurts and soy isolate powder do contain isoflavones, but competition with other ingredients and processing all affect amounts of isoflavones. The best way to know is to call the consumer line on the package of food and ask them if they have analysed for isoflavones. Soy oil doesn't contain isoflavones.
Q. Are isoflavones destroyed in the cooking process?
A. Isoflavones are fairly stable, so under normal home or institutional cooking methods they are not destroyed.
Q. How much isoflavones should one eat a day?
A. Optimal isoflavone intake to prevent or treat specific diseases is not known. At this time, overall health benefits of isoflavones as well as other phytochemicals are best met by eating a varied diet from all food groups, built upon a foundation of one serving of soyfood with plenty of whole grains, fruits, vegetables and other legumes each day.
PHYTOESTROGENS
THE STORY OF ISOFLAVONES AND SOY
Plants are super foods; orange plants are loaded with Vitamin A, the cruciferous family is rich in anti-oxidents, leafy greens contain high amounts of calcium, iron and vitamin C. In addition, plants have hormones; called phytoestrogens, from the Greek "phyto" for plant. And among the family of plant estrogens, isoflavones are potent cancer fighting agents.
In pre-menopausal women, estrogens are an integral part of the regulatory mechanism of the menstrual cycle; help the development of breast tissue; and contribute towards the secondary sexual differences between women and men. Estrogen production declines in post-menopausal women by up to 70 per cent, contributing to the uncomfortable symptoms of menopause, to weaker bones, as well as an increase in risk for breast cancer (the number two cancer killer of women). Prostate cancer is the number two cancer killer in men. The male hormone testosterone has a tendency to hasten the growth of prostate tumors. Phytoestrogens appear to slow down or inhibit cancerous cell growth in both men and women.
Isoflavones are found in the greatest concentration in soybeans and soy products . The main isoflavones are daidzein, genistein and genistin. They provide the essential benefits of estrogen to women without the threat of cancer. While an optimal daily amount of isoflavones is currently unknown, numerous experiments (see below) with soy products indicate that substituting a single serving of daily protein with a soy based food may provide this beneficial protection.
How? One suggested mechanism is that isoflavones compete with estrogen by mimicking estrogen's role in the body. For example, look-alike phytoestrogen "genistein" occupies the place in breast tissue cells of the real estrogen, thus preventing the more potent natural estrogen from converting normal cells into cancer cells. Another idea is based on the differences in menstrual cycle lengths between Japanese women living in Japan and in the U.S. Soy based foods are a staple in the Japanese diet. Japanese women have as much as 15 to 20 times as high a concentration of isoflavones in their blood as American women. Their menstrual cycle is on the average three to four days longer than American women, thus exposing them to fewer hormonal surges.
Evidence indicates that soy products may help relieve such menopausal symptoms as hot flashes and night sweats. In an 18 week study, researchers from the Bowman Gray School of Medicine in North Carolina examined the effects of soy on 43 women ages 45-55 experiencing these symptoms. For six weeks the women added 20 grams (under 1 oz, approximately 2 teaspooms) of powdered soy protein to their daily breakfast. For another six weeks, they added the same amount of soy protein to their diets, but split into two 10-gram doses. For a third six-week period, they added a look-alike powdered carbohydrate placebo. Significantly less severe hot flashes and night sweats were reported by those taking the soy. In addition, total cholesterol levels dropped an average of 10%. In the U.S., prostate cancer strikes one in 11 men, causing 38,000 deaths per year; but in Asia, where soy and other phytoestrogen containing foods are eaten more frequently, men fall victim to prostate cancer later in life and often die from other causes before their tumors become lethal.
How much? While there are no recommended daily allowances for Isoflavones, one daily serving of a soy food may assisst in the prevention of certain cancers, reduce menopausal symptoms, and provide a healthfull alternative to meat. Still not convinced? Take a look at a complete nutritional profile for various forms of soy, and browse through our introduction to the large variety of soy based foods .
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