Frequently Asked Questions
Is there a recommended soy food intake?
The FDA-approved health claim for soy protein reads "25 grams of soy protein a day as part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease." The soy protein content of soy foods varies from as little as 1-2 grams per serving to 18-20 grams per serving. On average, one can obtain 25 grams of soy protein by consuming four servings of soy foods that display the soy health claim on the front panel. Products that carry the health claim on the label contain at least 6.25 grams of soy protein per serving.
Is soy protein a complete protein?
Yes, soy protein is the only plant protein that is equivalent to animal protein. Soy foods contains all nine essential amino acids. The U.S. Department of Agriculture evaluates protein quality using the Protein Digestibility Corrected Amino Acids Score (PDCAAS). PDCAAS measures the amino acid pattern of proteins and factors in digestibility. Soy protein has a PDCAAS score of 1.0, equivalent to animal protein.
What are isoflavones?
Isoflavones are a form of phytoestrogens that have a chemical structure very similar to estrogen. Soy is uniquely rich in isoflavones, primarily genistein and daidzein. These isoflavones in soy foods thought to contribute to many of the protective effects that soy has shown in animal and in-vitro studies.
Is there a recommended daily isoflavone intake?
At this time, there is not enough research available for the FDA to make specific isoflavone intake recommendations. The FDA has approved a health claim stating that "25 grams of soy protein may help reduce the risk of heart disease." Twenty-five grams of soy protein contains approximately 50 milligrams of isoflavones. The isoflavone content of soy foods is available on the SANA soy food fact sheets or visit the isoflavone database on the USDA web site.
How does soymilk (soy milk) compare with cow’s milk?
Numerous fortified soymilks (soy milk) on the market today contain nutrients in level’s similar to cow’s milk and are good sources of calcium, vitamin A, riboflavin and phosphorus, as well as many other vitamins and minerals. Most soymilks are fortified with 300-400 milligrams of calcium, 120 IU of vitamin D, 500 mg vitamin A and 3 micrograms vitamin B12 per 8 ounces. Soymilk (soy milk) contains no cholesterol and is low in saturated fat.
Does the calcium absorption differ between soymilk (soy milk) and cow’s milk?
While the bioavailability of calcium in soymilk (soy milk) may be slightly less that cow’s milk, soymilk (soy milk) is still a significant source of calcium in the diet. In addition, studies have found that in comparison with animal protein, soy protein decreases calcium excretion, presumably due to the lower sulfur amino acid content of soy protein. Consequently, a soy-based diet is able to maintain calcium balance with a lower calcium intake.
Is soymilk (soy milk) appropriate for children?
Yes. Soymilks (soy milks) fortified with calcium and vitamin D can be part of a healthy diet for children over 12 months of age. The USDA’s 2000 Dietary Guidelines for Americans and Food Guide Pyramid for Young Children both identify fortified soymilk as a healthy food choice. Soy beverages are not a substitute for infant formula.
Is soy protein an allergen?
Soy protein is one of the eight major food allergens, along with proteins from milk, eggs, peanuts, tree nuts, fish, shellfish, and wheat. Although an individual could be allergic to any food, such as fruits, vegetables, and meats, the previously listed eight foods account for 90 percent of all food-allergic reactions. Individuals who experience allergies are advised by their physicians or nutritionists to avoid the foods that cause these reactions. Consumers allergic to soy protein can refer to the ingredient list on the product to identify what foods contain soy protein. The Food Allergy and Anaphylaxis Network is an excellent resource for people with food allergies. Contact www.foodallergy.org or 1-800-929-4040.
Do soy foods impact thyroid function?
There is no evidence that soy protein has an adverse effect on thyroid function in healthy humans who consume adequate amounts of iodine. Goiters are due to a deficiency of dietary iodine, not consumption of moderate amounts of soy protein as part of a healthy diet.
Do soy foods impact cognitive function?
Animal research suggests that soy, when taken in the diet, may be protective in the brain. One epidemiological study involving Japanese-American men found an association between increased tofu consumption and decreased cognitive abilities. However, additional clinical trials conducted, since the initial research was published, have found no negative effect of soy consumption on cognitive function. Additional studies have even found improved memory scores in people consuming soy foods.
Does soy impact breast cancer risk?
Early exposure to genistein provides lasting protection against breast cancer in the animal model. This finding has been supported by observational studies in humans, which have found that adolescent intake of soy was associated with reduced risk of developing breast cancer. Post-menopausal women at risk of breast cancer should discuss any diet changes or concerns with their health care provider.
What are protease inhibitors and do they have an adverse effect on growth?
Protease inhibitors are a class of proteins found in numerous plant foods, including rice, maize, and beans. Soybeans are particularly rich in protease inhibitors. There is no good evidence that soybean-derived protease inhibitors have an adverse effect on growth and human health. In fact, a growing body of data suggests that these compounds may in fact enhance human health through their cancer preventative effects.
Can people taking blood-thinning medication consume soy foods?
Yes, if you already consume soy foods as part of your diet, you will want to maintain that level of intake. If you are interested in adding soyfoods to your diet, please discuss this dietary change with your physician, so that your blood work can be monitored and medication adjusted if necessary. The dietary goal for individuals taking blood-thinning medication, such as warfarin, is to consume a consistent amount of vitamin K. The vitamin K content of soy products varies widely. Remember, you should discuss any dietary changes and vitamin/mineral supplement intake with your physician or pharmacist.
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