Women's Bodies, Women's Wisdom (157 page)

Dairy, nut, and wheat allergies are far more common than soy allergies.
Some people are unquestionably very sensitive to soy. (Soy does appear on the Food and Agriculture Organization’s list of the eight most prevalent food allergens. The list also includes milk, eggs, fish, crustaceans, wheat, peanuts, and tree nuts. Together, these foods account for about 90 percent of all food allergies.)

That said, in comparison with milk and nut proteins, soy is a relatively uncommon allergen—milk and peanut allergies are each five to six times more prevalent than soy allergies.
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In fact, the true incidence of soy allergy is quite low—it’s less than 1 percent of children and 0.1 percent of adults, according to double-blind, placebo-controlled studies.

Compared with other food allergies, soy reactions tend to be far milder. In a summary report of clinical food challenge studies, they were noted as minimal to mild 80 percent of the time, with the remaining 20 percent being moderate. No severe allergic reactions to soy were reported. In comparison, milk and peanut allergens produced minimal to mild symptoms in 50–70 percent of cases, moderate symptoms in 20–30 percent of cases, and severe symptoms in 10–15 percent of cases.

In my experience, the vast majority of people with food allergies are sensitive to wheat and dairy foods, not soy. And reactions to wheat and dairy often trigger crossover reactions to other foods.

Bloating and gas from soy don’t indicate an allergy.
Some people are sensitive to the nondigestible sugars and fiber in soy. These can cause the same abdominal bloating and gas that you’d experience from ingesting the sugars and fibers in beans—or even the lactose in milk.
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Whenever you add legumes of any kind to your diet, the bowel flora take a while to adjust. But you don’t have to suffer—take digestive enzymes and probiotics to keep the intestines in good form and reduce discomfort.

Phytates are part of a healthy diet.
If you’ve read any anti-soy literature, you’ve probably heard that soy is high in phytates, which can inhibit absorption of important nutrients from the gut. This is a half-truth. Plants store phosphorus (an essential nutrient for plants and animals) in their seeds to support the growth of young seedlings. This phosphorus is stored in the form of phytate (inositol hexam-etaphosphate). Plant phytates are considered by some to be antinutrients, because phytates consumed in the human diet can compete with essential minerals (for example, iron and zinc) and inhibit absorption in the gut.

However, phytates are also important food constituents that not only act as natural food-preserving antioxidants but also help to reduce risks of heart disease and cancer in those who consume whole grains, beans, seeds, and nuts.

Though soybeans contain significant amounts of phytate, so do whole grains, beans, and seeds. There’s robust scientific literature supporting the fact that these foods are important constituents of a healthy diet. So avoiding soybeans to avoid phytates doesn’t make sense. That said, isolated soy protein contains far less phytate than whole soybeans.

Both nonfermented and fermented soy products have their place.
Soy foods fall into two broad categories: nonfermented and fermented. Non-fermented soy foods include soy nuts, edamame (whole soybeans), soy milk, and tofu (bean curd). Fermented soy products include tamari, soy sauce, miso, tempeh, and natto.

Though opinions vary widely, tending to favor fermented soy over nonfermented, there is no scientific consensus on which is better. Here’s why:

Fermenting soy foods increases isoflavone bioavailability. However, fermenting a soybean also decreases the actual isoflavone content of the food. That’s why typical intakes of nonfermented soy foods result in a higher intake of isoflavones.

Fermented soy foods can be easier for some to digest, but taking digestive enzymes and probiotics, as mentioned earlier, can easily make nonfermented soy more digestible if this is a problem for you.

Fermented soy products have lower phytate levels than nonfer-mented soy. But as I said above, phytates aren’t necessarily bad for you. Mineral levels of people consuming a healthy mixed diet made up of soy and other phytate-containing foods have not been found to be adversely affected.

Fermented soy products can be quite high in sodium, a known risk factor for stomach cancer. A review of soy intake and stomach cancer indicated that risk did increase with intake of fermented soy foods (mainly miso) but decreased with intake of non-fermented soy foods (mainly tofu).

Soy has well-documented health benefits.
Many studies have strongly suggested that soy protein has benefits for the cardiovascular system, bones, and overall health, including conferring a decreased risk of some kinds of cancer, among them breast cancer. In a review of twenty-six animal studies of experimental carcinogenesis in which researchers used diets containing soy or soybean isoflavones, 65 percent reported protective effects, while none reported any increased risk of tumors. Soy protein has also helped many women find relief from menopausal symptoms.

Yet the hundreds of studies done on soy are hard to interpret and to use as a basis for specific recommendations because some used whole soy, some isolated isoflavones, and some fermented soy in foods such as miso and tempeh. It’s also fairly difficult to tell whether the health benefits associated with soy are a result of overall dietary improvement from decreasing animal protein in the diet and adding more vegetables or whether they’re strictly from soy. Here are some highlights:

Cancer/ breast cancer.
Consumption of nonfermented soy products, such as soy milk and tofu, tended to be either protective against both hormone- and non-hormone-related cancers or not at all associated with cancer risk. In large population studies, soy consumption has been associated with a decreased risk of prostate, breast, and colon cancers.
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Soy products contain five known classes of anticancer agents, including isoflavones (phytoestrogens, which are present in many foods, but uniquely high in soy), protease inhibitors, phytate, phytosterols, and saponins, as well as other potential anti-carcinogens such as phenolic acids, lecithin, and omega-3 fatty acids. Isoflavones are currently the most intensively researched soy phyto-chemical with respect to breast cancer, although a growing body of literature supports protease inhibitors as anticarcinogens. Also, the Bowman-Birk protease inhibitor (BBI), found in soy, has been shown to be nontoxic and prevent and suppress carcinogenesis in animal models. A concentrated form of BBI (referred to as BBIC) has been given investigational new drug status for use in human cancer prevention trials.

Soy contains two primary isoflavones, genistein and daidzein. Both appear to be cancer-protective. They are antioxidants that help to neutralize cellular inflammation within the body, a known precursor for cancer. Isoflavones are also estrogen modulators; dampening the potentially harmful impact of not only the more potent estrogens produced by the body but also environmental substances that have estrogen-mimicking properties (xenoestrogens).

Several epidemiological studies have specifically examined the association between soy consumption and the incidence of breast cancer. Many, but not all, have shown that soy intake can be protective. In a study involving 200 Singapore Chinese women with breast cancer and 420 matched controls, a decreased risk of breast cancer was associated with high intakes of soy products in premenopausal women.
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A more recent case-control study done at the University of Southern California interviewed 597 Asian American women with previous incidence of breast cancer and 966 controls.
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Risk of breast cancer decreased with increasing frequency of tofu consumption in both pre-and postmenopausal women. A 2003 study of 21,852 Japanese women ages forty to fifty-nine found that women with the highest intake of soy isoflavones reduced their risk of breast cancer by up to 54 percent compared with women with the lowest intake of soy isoflavones.
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Perhaps the breast cancer debate can be best summed up by the conclusions of an international group of nearly twenty researchers from around the world, sponsored by the Council for Responsible Nutrition, who met in Milan in 2009 to evaluate the research on isoflavones and their implication in cancer. The research presented overwhelmingly supported the idea that isoflavones do not have an effect on established markers for breast cancer risk. In fact, the data instead showed that soy may improve the prognosis of breast cancer patients.
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Cardiovascular disease.
Soy protein consumption has been linked to a small (3–5 percent) decrease in LDL (bad) cholesterol.
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Also, because of their antioxidant and estrogenic activities, soy isoflavones may benefit cardiovascular function. But the significance of all this has yet to be studied thoroughly.