Research continues to accumulate showing that a diet rich in soy may have a dramatic impact on reducing breast and other cancer risk-as well as confer additional benefits on health. However, a number of new studies appear to debunk the body of anecdotal evidence that soy products may alleviate hot flashes in breast cancer survivors.
The evidence that diet can play a role in the development of breast cancer initially came from population and migration studies of Japanese immigrants to North America. Demographic evidence showed that second- and third-generation immigrant women had a higher incidence of breast cancer than their counterparts back in Japan.
Breast cancer rates of North American-born Japanese women and later-generation Japanese immigrants were almost identical to the higher rates for Caucasian North Americans. Conversely, the most recent immigrants had an incidence rate that fell between that of their predecessors and that of Japanese women residing in Japan. Such findings support the theory that environmental factors can play an important role in the origins of breast cancer.
Another study found a significant relationship between a lowered risk of breast cancer in Japanese women and the consumption of miso, a soybean paste soup. In a similar study of Singaporean women, a diet high in soy products was found to confer a lower risk of breast cancer in pre-menopausal women, although there was no effect observed in post-menopausal women.
Such research further reinforces the recommended inclusion of at least one serving of soy protein per day in an otherwise diverse diet that has a high content of fruit, vegetables and grains. Such a diet appears to have multiple positive health benefits-even beyond reduced breast cancer risk. These include a decreased risk of endometrial cancer, reduced incidence of heart disease and osteoporosis, and even lower cholesterol levels.
A University of Southern California Medical School study on the anti-cancer effects of soy concluded that one specific component of soy-genistein-may inhibit the growth of cancer cells.
"Soy products contain high levels of genistein, a phytoestrogen that is a potent inhibitor of cell proliferation," the study said. It noted that genistein has been found to inhibit both the growth of carcinogen-induced cancers in rats and human leukemia cells transplanted into mice.
The researchers found that genistein suppresses the production of harmful stress proteins in cells; these stress proteins, which include heat-shock proteins (HSPs) and glucose-regulated proteins (GRPs), normally help cancer cells survive destruction by the immune system.
"Genistein used either intravenously ... or orally ... offers an alternative, pharmacologic approach for the suppression of the mammalian stress response," according to the study, which was published in the Journal of the National Cancer Institute.
Genistein is one of several isoflavones found in soy, and some scientists have attributed many of the soybean's positive health effects to its high concentration of isoflavones. For example, a study by the Cancer Research Center of Hawaii found that isoflavones in soy, including genistein and daidzein, may reduce the risk of uterine cancer. Other studies have also found that soy may help prevent heart disease, osteoporosis, bone disease and other forms of cancer, including breast and kidney cancer.
The University of Southern California study also compared Asian diets, which are high in soy intake, with the diets of Americans, which are low in soy intake. "The much lower risk of breast, colon and prostate cancers in Asians who consume 20 to 30 times more soy per capita than Americans raises the question of whether compounds in the soy diet may be acting as natural chemopreventive agents," said lead author Dr. Amy Lee.
"Soy products such as tofu contain high levels of several isoflavonoids, including genistein, which has been identified as a potent inhibitor of cell proliferation ... with antioxidant properties," she added.
And yet, the exact role that soy-based compounds play in minimizing cancer risk is not without controversy.
At the recent annual meeting of the American Association of Cancer Research, Dr. Andreas Constantinou of the University of Illinois presented findings that soybean protein mixes without isoflavones may be more effective in deterring mammary tumor growth than soy proteins which are enriched with isoflavones.
Constantinou's team gave various soy-based dietary supplements to groups of laboratory rats and then induced breast cancer tumors. They found that all of the soy-containing compounds resulted in a reduced incidence of mammary tumors, but the rats receiving the isoflavone-depleted mix had a much more significant reduction in the number of tumors compared with the other groups.
Although the results are preliminary and based solely on laboratory experiments, Constantinou suggested that isoflavones might not be the primary soy component involved in suppressing mammary tumor growth.
Furthermore, despite anecdotal claims to the contrary, a new study has added to the growing body of evidence that soy may not have a benefit in relieving hot flashes experienced by cancer survivors.
Writing in the Journal of Clinical Oncology, a team of researchers led by Dr. Charles Loprinzi of the Mayo Clinic in Rochester, Minnesota, gave two groups of breast cancer survivors either soy-based phytoestrogens or a placebo to see if their symptoms of hot flashes were alleviated.
Hot flashes are a common problem for cancer survivors. Women with breast cancer are particularly susceptible, as some chemotherapy drugs can cause premature menopause. Tamoxifen can also contribute to hot flashes.
Many cancer patients have tried a variety of complementary therapies to reduce their discomfort from hot flashes, in particular soy-based products. Soy contains phytoestrogens, which are plant-derived nonsteroidal compounds that share some biological properties with natural estrogens. This has led some researchers to believe that soy may have estrogen-like effects and thus alleviate hot flashes.
To test this theory, Loprinzi's team gave 177 breast cancer patients a soy-based product and 155 patients a placebo. Over a four-week period, the women recorded hot flash frequency and intensity as well as other side effects.
At the end of the period, 33 percent of the patients expressed a preference for the soy preparation, but fully 37 percent preferred the placebo and thirty-one percent did not have a preference. The researchers concluded that there was no basis to suggest that the soy product was more effective in reducing hot flashes than a placebo. In fact, there was a mild trend for the placebo group to do better than the soy group.
Much more research is needed to clarify the exact role that soy-based products can play in minimizing cancer risk. While demographic evidence is apparently strong, the exact compounds in soy-based foods that confer this benefit remains unclear. Nonetheless, dozens of clinical trials are now underway to further understand the exact role that soy-based products and other dietary factors can play in the prevention of breast and other cancers.
SOURCES:
Journal of the National Cancer Institute, 1998; 90:381-388
The Journal of Clinical Oncology, March 2000; 18:1068-1074
American Journal of Clinical Nutrition, Sept. 1999; 70(3 Suppl):439S-450S
Abstracts from the 91st meeting of the American Association for Cancer Research (www.aacr.org)
Hopkins post script: Johns Hopkins will be conducting 2 research studies using soy to further aid in providing answers to the questions raised in this article.
Soy, Not Isoflavones, Fights Breast Cancer
Soy consumption has been shown to inhibit breast cancer, but isoflavones-a soy component assumed to provide those anti-cancer benefits-may not be that important, a new study has concluded.
The study casts doubt on the benefits of using purified soy isoflavones to cut the risk of breast cancer.
Researchers at the University of Illinois at Chicago (UIC) tested purified isoflavones against soy protein mixes with and without isoflavones in female rats to determine their effectiveness in reducing the incidence and the number of mammary gland tumors.
"There are well-established studies showing that soy is effective in helping prevent tumors. The assumption was that isoflavones would be the active ingredient, but we found a lot of surprises," Dr. Andreas Constantinou, a surgical oncologist at UIC's College of Medicine, said at an American Association of Cancer Research meeting.
Although all the compounds studied reduced the incidence of tumors, the soy protein mix without isoflavones was the most effective in decreasing the number of tumors, he said.
Constantinou suggested that the anti-tumor ingredient in the soy mixture works by increasing the production of two detoxification enzymes that shield cells from harmful substances called free radicals.
Other components of soy that could be responsible are dietary fiber, phytic acid or lignans, the researcher said.
Purified isoflavones have become commercially available as women at risk for breast cancer seek preventive measures against the disease.
Studies have shown an inverse relationship between the consumption of soybean products and breast cancer risk in premenopausal women.
In addition, the incidence of the disease is lower in Japan and regions of China-where a large percentage of daily caloric intake is from soybeans-than in Western industrialized countries where little or no soy is included in the diet.
"Based on these findings, I recommend against using purified soy isoflavones," Constantinou said.
Source: CNN/Reuters
Doubts Cast on Benefits of Shark Cartilage
Actually, sharks do get cancer. That discovery challenges a small industry based on the belief that shark cartilage contains some beneficial cancer-fighting substances.
Dozens of brands of shark cartilage supplements are sold in drugstores, promoted as treatments for cancer, arthritis and aging. The stuff is even put in dog biscuits.
One of the chief arguments behind this is the idea that sharks don't get cancer.
``That idea is wrong. Sharks do get cancer,'' said John C. Harshbarger of George Washington University.
Harshbarger, who heads the federally sponsored Registry of Tumors in Lower Animals, described 40 cases of tumors that have been found in sharks and their close cousins, the skates, rays and chimerids.
Harshbarger presented the data at a meeting in San Francisco of the American Association for Cancer Research. He said that most of the cases have long been known to scientists, although he added two new ones-kidney cancer in a dogfish shark and lymphoma blood cancer in a sandbar shark.
``This is good science that shows us that sharks can get cancer,'' commented biologist John Coffey of Johns Hopkins University. ``I don't think there is any benefit to buying shark cartilage and eating it, any more than I think that eating a rabbit will make me run faster.''
Shark cartilage proponents dismissed the latest work as nothing new.
``It's true that some sharks get cancer. I said this in my book,'' said William Lane, author of the 1992 book ``Sharks Don't Get Cancer.'' ``My publisher thought it would be bad to call it, `Almost No Sharks Get Cancer.'''
Still, Lane said, cancer is far less common in sharks that in other ocean creatures.
Harshbarger questions that assertion, too. He said that all of the shark cases reported so far are anecdotal discoveries made mostly by sharp-eyed biologists. No one has ever done a systematic survey of sharks to see how often they get cancer or whether they are less prone to the disease than other fish.
In theory, shark cartilage might stop cancer by blocking the growth of new blood vessels, a necessary step in tumor spread. However, biologist Gary K. Ostrander of Johns Hopkins said there is no animal or human research to support its anticancer properties.
A study published in November 1998 concluded that shark cartilage pills were ineffective in 47 patients with advanced breast, colon, lung, and prostate cancer.
A much larger study will begin later this year at the Mayo Clinic to test shark cartilage on 600 terminally ill patients with breast and colon cancer.
The study will be sponsored by the National Institutes of Health and Lane Labs, a company founded by Lane's son Andrew, that sells shark cartilage.
Harshbarger said that 23 of the 40 tumors in the registry are in sharks, while the rest are in their close relatives. The bodies of all these creatures contain cartilage but no bone.
Source: Associated Press
White Tea May Help Fight Cancer
White tea appears to have more potent anticancer qualities than green tea, according to studies performed at the Linus Pauling Institute of Oregon State University.
The researchers tested the tea to determine whether it could help prevent genetic mutations in bacteria, and colon and rectal cancer in cancer-prone rats.
The rats were offered white tea-at a strength equivalent to steeping a tea bag in a cup for five minutes-instead of water for eight weeks.
In both experiments, white tea was shown to have a strong protective effect, said Dr. Gilberto Santana-Rios. By some measures, white tea offered twice the protection of water alone, and significantly more protection than green tea, he said.
Although all teas are made from the same type of plant, they differ in which parts of the plant are collected and how they are processed.
The most common tea in North America and much of Europe, black tea, is also the most heavily processed. For black tea the leaves are withered, rolled, roasted and dried, and when steeped they produce a characteristic dark beverage.
For white tea, the leaves and white-colored buds of the plant are merely steamed and dried, leaving a mixture that looks like dried basil flecked with small white buds. When steeped in hot water, the result is a pale liquid with a taste reminiscent of green tea.
Source: Reuters Health
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