|Pueraria mirifica is a common ingredient in many such products. The plant-based estrogen mimics human female hormones and can at least theoretically stimulate the development of secondary female sex characteristics like the breast.
Medical studies, however, have not documented this outcome with use of these products, most likely because the phytoestrogens are very weak and present in low concentration. While any perceived breast improvement is probably more of a placebo effect than real, the risks of stimulating cancer or interfering with normal hormone interactions remain unknown.
The Singapore Health Sciences Authority cautions the public not to risk adverse health effects and serious complications by purchasing food items carrying dubious health claims.
APSG Comment: If the young Singaporeans who use these products appear naive on first reading, they shouldn't. Thousands of unproven and untested "nutritional supplements" and food products are available for sale over-the-counter in the United States and other countries.
If the packaging on a product states in small print that the FDA has not evaluated any health claims, the manufacturer is essentially off the hook. An important key word in labeling is "promote" as opposed to "cure" or "improves." As long as an item is noted to "promote heart health," "promote anti-aging," or "promote breast health," it's legal to imply a wide variety of equally unlikely health benefits.
Don't be shocked to find these same breast enhancement cookies on the shelf at your local health food store.