New research published today reveals that consuming soy could have a "severe" impact on a genetic heart condition that affects one in 500 people, though the authors caution that the effect has so far only been observed in male mice.
The study, which appears in today's issue of the Journal of Clinical Investigation, is the first of its kind amidst a body of evidence linking soy to a number of health benefits.
According to scientists at the University of Colorado, male mice carrying the mutation for hypertrophic cardiomyopathy, or HCM, were severely affected by a soy diet, exhibiting progressively enlarged heart muscles and eventual heart failure.
But when the mice were switched to a diet of milk protein casein, their condition "improved markedly," said the researchers.
HCM, primarily a genetic condition, is the leading cause of death in young athletes, and often remains undiagnosed in its milder forms.
The new findings are likely to cause a stir in the food industry, as manufacturers are increasingly using soy in their formulations on the back of the positive science surrounding the product.
Indeed, according to market researcher The Freedonia Group, new research and the approval of health claims will contribute to 5.1 percent annual growth in demand for soy in the US over the next five years, with overall demand for soy products set to reach $8.65 billion by the end of the decade, compared to $6.75 billion in 2004.
According to lead author of the new study, Professor Leslie Leinwand, the research shows that "at least in mice, diet can have a more profound effect on heart disease than any drug that we could imagine."
"We have no information about how this work might translate into humans," she told FoodNavigator-USA, adding that there is also no evidence that healthy animals could be affected.
"We only see the negative effects on a specific genetic heart disease model and only in males," she said.
Female mice carrying the mutation for HCM apparently remained "relatively unaffected" by the soy diet due to the fact that they are constantly exposed to naturally circulating levels of estrogen compounds and are therefore less sensitive than males to the change in estrogen level as a result of the soy diet.
Leinwand also added that "the concentration of soy protein in the mouse diet is likely much higher than in a person eating tofu and edamame on a regular basis, however the addition of high concentrations of plant estrogens in the form of dietary supplements for humans can be very high."
According to the American Soybean Association (ASA), more research is still needed before claiming that soy could have a negative heart health impact.
"You need several studies to really see a trend. This is just one message, linked to mice and not humans, and affecting only a very niche sector that carries the genetic disease. It is a limited message and does not undermine all the positive messages so far available about soy," said ASA technical marketing consultant Ignace Debruyne.
And according to Lisa Salberg, president of the nation's Hypertrophic Cardiomyopathy Association, the new study "goes against everything I have ever heard about soy diets and heart disease."
"But if they have found a food to alter the progression of the disease, whether positive or negative, it is extremely meaningful as it gives us more roads to look down," she added.
Until now, most scientific studies have focused on the health benefits of soy, and there is a growing awareness amongst consumers that the product is high in fiber, protein and minerals yet low in saturated fat and free of cholesterol.
In 1999 the FDA approved an unqualified health claim linking consumption of soy foods to a reduced risk of coronary heart disease. According to a 2000 report in FDA Consumer, consumption of soy foods increased 20 percent per year since 1995 and the approval of this claim led to surging interest.
The link between soy and heart health was also recently reinforced when a study published in November revealed that soy protein containing isoflavones could help reduce two strong indicators for coronary heart disease in postmenopausal women.
Other studies have also indicated that components found in soy could help reduce cholesterol, prevent high blood pressure, alleviate menopause symptoms and maintain bone density.
On the down side, a medical study published in June in the UK claimed the soy component genistein may damage human sperm.