Breast cancer. Eating a high-soy diet is linked to a slightly reduced risk of developing breast cancer. Researchers think early exposure to soy may be key. Asian women who eat a traditional diet high in soy seem to be less likely to develop breast cancer. This benefit continues even when Asian women move to western cultures, where soy is less likely to be a regular part of the diet. This suggests that exposure to soy early in life (i.e., before menopause) provides the most protection against breast cancer.
Diabetes. Most evidence suggests that taking soy products reduces blood sugar levels in people with diabetes. One study suggests that eating a whole soy diet, not just the protein from soy, reduces blood sugar in people with and without diabetes. However, there is also some evidence that suggests that soy and soy protein don’t affects blood sugar in people with diabetes.
Kidney disease in people with diabetes. Soy isoflavones might help prevent or treat kidney disease in people with diabetes.
Diarrhea. Feeding infants formula supplemented with soy fiber, alone or together with rehydration solution, seems to reduce the duration of diarrhea compared to cow’s milk formula or rehydration solution alone. However, in some studies formula supplemented with soy was no more beneficial than cow’s milk formula. In adults, early evidence suggests that taking soy fiber does not decrease the incidence of diarrhea.
Trouble digesting the sugar galactose (galactosemia). Feeding a soy-based formula to infants who have galactosemia seems to be helpful.
Trouble digesting the sugar lactose (hereditary lactase deficiency). Feeding a soy-based formula to infants who have hereditary lactase deficiency seems to be helpful.
Trouble digesting the sugar lactose (lactose intolerance). Feeding a soy-based formula to infants who have lactose intolerance seems to be helpful.
High cholesterol. Eating soy protein in place of other dietary protein or using soy fiber products seems to slightly reduce total cholesterol and “bad cholesterol” (low-density lipoprotein (LDL) cholesterol levels). However, not all evidence is positive. Some studies have shown no significant benefit of soy protein on cholesterol levels.
Kidney disease. Taking soy protein by mouth seems to reduce protein in the urine in people with kidney disease.
Menopausal symptoms. Eating soy protein seems to help hot flashes caused by menopause. However, it does not reduce other symptoms of menopause, such as vaginal dryness or itching. Also, soy does not seem to help hot flashes in women with breast cancer.
Osteoporosis. Most evidence suggests that soy protein can increase bone mineral density (BMD) or slow BMD loss in women near or beyond menopause. Soy might also reduce the risk of fractures in some women. Soy does not seem to affect BMD in younger women.