Isoflavones act like the female hormone estrogen in the body, and have been studied closely to determine if they may help treat estrogen deficiency-related conditions such as breast cancer, prostate cancer and osteoporosis.
Huang and colleagues at the Hong Kong Polytechnic University performed a study on soy milk last year to determine the effect of heat on three isoflavones: genistein, daidzein and glycitein. When soy milk undergoes in-bottle sterilization, it is heated at around 250 degrees Fahrenheit for five minutes. This process destroys "about 87 percent of daidzein, 72 percent of glycitein and 17 percent of genistein,” the researchers said.
They added that when soy milk is pasteurized, or heated to 203 degrees Fahrenheit for one hour, daidzein degrades 77 percent and glycitein degrades 66 percent, but genistein surprisingly increases by 33 percent.
Currently, China's soy milk industry -- which produced around 300,000 tons of milk last year -- tends to focus on protein and vitamin content over isoflavones. However, soy milk industry expert Tu Shunming, of China's National Research Institute of Food and Fermentation Industries, does not think soy milk sales will suffer because isoflavones are a secondary concern.
"China has long practiced heating soy milk to temperatures ranging from 95 to 110 degrees Celsius (203 to 230 degrees Fahrenheit) to asepticize it," Tu said. "And Chinese women are still healthier than Western women, a phenomenon that led the West to conduct research into soy."
"This research demonstrates yet again how heat processing destroys many of the nutritional benefits in natural foods," said Mike Adams, a consumer health advocate and holistic nutritionist. "It's also why raw foods and living foods provide such an abundance of natural medicine and high-density nutrition. I switched from soy milk to raw almond milk over a year ago for this very reason, and I now make my own raw almond milk using a Vitamix blender."