Soybeans are the most widely used, least expensive, and least caloric way to get large amounts of protein with very little fat and no cholesterol. You can eat soybeans in many forms, including tofu, the beans themselves (also known as edamame), soy milk, miso, and soy powder.
There are a lot of health-related phytochemicals in soy. Protein kinase inhibitors help keep cell growth and activity normal. Phytosterols and saponins help regulate cholesterol. Phenolic acid and phytates are antioxidants.
Then there are the isoflavones, which are weak phytoestrogens. Isoflavone levels vary in different types of tofu and soy milk products. Your body's estrogen is much, much stronger than the estrogen-like isoflavones in soy. So if the weak soy substance replaces the natural high-strength estrogen in cells, then maybe the soy will protect against cancers that would prefer a stronger estrogen signal.
Soy is often promoted as a healthy protein alternative for people who would rather not eat meat. Research about the effects of soy on cancer risk reduction has been mixed. Much of it has come from observing cultures such as the Japanese, who eat much more soy and begin eating it at a much younger age than people in Western countries.
In fact, the average woman living in East Asia eats about 10 times the quantity of soy foods as the average woman in the United States. Yet, East Asian women have lower rates of hormone-receptor-positive breast cancer than women in the United States.
The "soy story" and its possible connection to breast cancer is complicated by other factors. Most women living in Asia depend on soy as their main source of protein. They consume only small amounts of beef, chicken, and pork—which means less animal fat and other possibly unhealthy substances (such as growth hormones and antibiotics) in these animal protein sources. Also, compared to the average woman in the United States, the average Asian woman:
eats more fresh vegetables
is closer to her ideal body weight
is more physically active
is less likely to consume significant amounts of alcohol
All of these other factors add up to produce a healthier lifestyle and a lower overall risk of breast cancer in Asian women living in Asia.
It's not clear if soy isoflavones affect breast cancer, especially hormone-receptor-positive breast cancers. Isoflavones may affect hormonal therapy's ability to do its job if both of these molecules compete to get into the same estrogen receptors. If isoflavones deliver a weaker estrogen signal to the receptor compared to tamoxifen (and your body's estrogen), then the isoflavones might be able to decrease breast cell growth that's estrogen-dependent. But if the isoflavones give breast cells a stronger estrogen signal than tamoxifen, that's a problem.
Until the issue becomes clearer, many doctors recommend that women who take hormonal therapy or who have estrogen-receptor-positive breast cancer avoid soy supplements because they contain high concentrations of isoflavones. But in general, it's fine to eat moderate amounts of soy foods as part of a balanced diet. One to three servings of soy a day (a serving is about a half cup) is similar to an average Japanese woman's daily soy intake. If you are taking hormonal therapy to fight off a hormone-receptor-positive breast cancer, and you are concerned about any phytoestrogen effects, ask your doctor or registered dietitian about how much soy you can eat.
Nutrition and Cancer: Exciting Advances for 2002!
Gregory K. Ogilvie, DVM, Diplomate ACVIM (Internal Medicine, Oncology) Professor and Head of Medical Oncology, Animal Cancer Center, Colorado State UniversityFt. Collins, CO, USA
Cancer is one of the most common diseases in dogs and cats in the United States, Western Europe and Japan. Cancer cachexia is the most common paraneoplastic syndrome in veterinary medicine. This paraneoplastic syndrome of dogs and cats with a wide variety of malignancies results in profound alterations in carbohydrate, protein and lipid metabolism that subsequently results in anorexia, fatigue, impaired immune function, poor performance and weight loss in the face of adequate nutritional intake.1 These profound alterations in carbohydrate, protein and lipid metabolism have been documented in dogs and probably in cats with cancer, even before evidence of cancer cachexia was clinically apparent.1-11
The importance of cancer cachexia is underscored by the knowledge that animals and people with cancer cachexia have a decreased quality of life, poor response to treatment, and a shortened survival time when compared to those with neoplastic diseases but do not exhibit clinical or biochemical signs associated with this condition.1-8 Therefore, it is obvious that cancer and cancer cachexia are of tremendous importance to the practicing veterinarian.
Nutritional therapy is a key component for the treatment of cancer cachexia and for actually helping control malignant disease in some situations. Specific nutrients can be used as powerful tools to reduce toxicity associated with chemotherapy, radiation therapy, and is important to enhance healing subsequent to surgery. There is little question that nutritional intervention must begin early and must be followed through aggressively to gain maximum benefit.....long before the patient exhibits evidence of weight loss, debilitation, or anorexia begin which can in turn enhance response to therapy and improve quality of life.