The U.S. Food and Drug Administration has approved only one health claim for soy: “reducing the risk of cardiovascular disease in individuals who consume a low-fat diet and include exercise in their health regimen.”
But researchers, with mixed results, have been eager to test whether plant estrogens in soy, called isoflavins, may help alleviate some of the symptoms of menopause as well.
Six researchers from The University of California Davis School of Medicine, Davis, Calif., the University of Massachusetts Medical School, Worcester, Mass., and the University of California Los Angeles David Geffen School of Medicine, Los Angeles, published their paper earlier this year after sampling 1,651 women in various geographic locations in the United States.
In “Phytoestrogen and fiber intakes in relation to incident vasomotor symptoms: Results from the Study of Women’s Health Across the Nation,” the researchers found neither soy nor fiber consumption had preventive effects on hot flashes and night sweats.
Focusing on soy, the study did not prescribe a set intake for the subjects to consume each day. Instead, it relied on subjects’ self-reporting of what they ate. Study participants generally consumed small amounts of soy, begging the question of what the study outcome might have been if the women had ingested much larger daily amounts of soy?
Mark Messina, a Ph.D. nutritionist at Loma Linda University in Loma Linda, Calif., directs the Soy Nutrition Institute and freely admits to “a conflict of interest” regarding soy, said he doubts the efficacy of the study because of the small amounts of soy the women consumed. Because this was an epidemiological study rather than a clinical trial, the researchers reported the amount of soy consumed by the study participants. And they consumed almost no soy, Dr. Messina said.
“They ate 0.5 milligram per day on average and there are 25 milligrams in a cup of soy milk,” which is one serving, he said. “How could a study based on a pattern of miniscule soy consumption produce a viable outcome?” he said.
He also questioned the whole premise of the study, which focused on prevention rather than alleviation of ongoing symptoms.
“How many women would consume soy for several years until they reached menopause on the chance it would prevent hot flashes?” he said. It made more sense to see if soy helped reduce the number of hot flashes in women already suffering them, Dr. Messina said.
As it happens, he worked on a meta-analysis of 17 studies evaluating clinical trials where women took soy supplements or placebos to see if their existing hot flashes improved on a soy regimen. The results showed women ingesting soy supplements had a 21% greater reduction in hot flashes compared with women given a placebo.
The lead author of the prevention study, Ellen Gold, Ph.D., responded to an email request from Food Business News asking for her response to Dr. Messina’s critique. She said he was “probably right” that the daily amount was very small, because intake from food in Western diets is usually less than intake from supplements. She had nothing to say about whether small amounts of isoflavins had any ability to affect outcomes. Instead, she emphasized there haven’t been any previous studies that took exactly the same tack as the one she worked on.
“Our intent was to look at whether phytoestrogen intake prevented onset of hot flashes in women who were not yet menopausal,” she said, noting this approach had not been studied before.
There are likely to be more studies looking at possible health effects of soy. The medical community switched a few years ago from being advocates for hormone replacement therapy using medications containing female hormones to being cautious in recommending it because of health risks. Since then, clinicians have examined hypotheses that soy foods, because they contain plant estrogens, may be a natural alternative to manufactured estrogen in the treatment of menopausal symptoms.
The headlines have indicated the roller-coaster nature of this line of inquiry. In August 2011, the Huffington Post declared “Soy doesn’t stop bone loss or ease menopause symptoms: study.” In August 2012, Reuters Health wrote: “Does soy help cool hot flashes after all?” And the New York Times summed the Gold study with this headline in November 2012, “Doubt on soy and fiber as menopause aid.”