No clinical trials have investigated the efficacy of soy -- or any other botanical product -- to increase breast size, according to Mayo Clinic physician Sandhya Pruthi. Nevertheless, soy-based foods and supplements may help to increase breast growth in women with fewer side effects and lower costs than cosmetic surgery or prescription drugs. Medline Plus, a service of the U.S. National Institutes of Health, notes soy's possible use as a breast enhancer. However, until scientists have conducted further clinical trials, the NIH regards this use as theoretical.
According to the NIH, soy protein contains natural compounds that are chemically similar to estrogen. These "phytoestrogens" include medicinal isoflavones like genistein, which have an estrogen-like effect on the human body. Because estrogen plays a role in the development of breast tissue, soy may provide the hormonal boost necessary for improving the size and shape of breasts.
A diet rich in soy can be surprisingly affordable. Minimally processed soy foods like tempeh, tofu and soy milk contain large quantities of isoflavones but cost little more than their meat- or dairy-based counterparts. High-soy diets may be a viable alternative to cosmetic surgery.
Unlike hormone-affecting drugs and cosmetic surgery, a diet rich in soy protein does not require a prescription. However, caution is advised for certain individuals. While the NIH considers dietary soy to be safe for those taking anticoagulant drugs like warfarin, soy isoflavone supplements may theoretically increase the risk of an adverse reaction. Isoflavones in soy can also alter the way the liver metabolizes certain drugs, according to the NIH. People with medical conditions should consult a qualified physician or dietitian before pursuing a high-soy diet.
Unlike pharmaceutical and surgical breast enhancement protocols, soy protein does not cause breast tenderness. In fact, NIH reports that soy may prevent cyclical breast pain associated with menstruation.