Soy Might Worsen Heart Condition

Male mice prone to hypertrophic cardiomyopathy did better on milk-protein diet, study finds

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By Janice Billingsley
HealthDay Reporter

WEDNESDAY, Jan. 4, 2006 (HealthDay News) -- In an animal study showing strong links between diet and a specific type of heart disease, researchers report that consuming soy might adversely affect the condition called hypertrophic cardiomyopathy.

University of Colorado scientists found that when male mice who carried a gene mutation associated with hypertrophic cardiomyopathy (HCM), a disease in which the heart muscle thickens abnormally, were taken off their normal soy diets, their heart function improved significantly compared to HCM male mice who stayed with soy. Female mice with HCM did not show the same significant change.

"I was struck by the massive impact that diet had on so many functions of the heart -- the all-encompassing effect of diet was so striking," said study co-author Leslie A. Leinwand, chairman of the Department of Molecular, Cellular and Developmental Biology at the university.

That said, Leinwand is not sounding the clarion call for those with heart disease to avoid soy.

"I would feel pretty uncomfortable making any kind of recommendation about what physicians should say to patients, as these are mice, not humans," she said.

HCM is a cardiovascular disease occurring in one of every 500 individuals, according to the American Heart Association. Usually caused by a genetic mutation, the disease creates abnormal thickening of the heart muscle, which interferes with the healthy function of the heart. Symptoms can include shortness of breath, chest discomfort and palpitations that may be a sign of life-threatening arrhythmias, Leinwand said.

Patients with hypertrophic cardiomyopathy are at higher risk for sudden death than the normal population, and can be affected at a young age. HCM is a well-known cause of sudden death in athletes, according to the National Institutes of Health.

The study findings appear in the Jan. 4 issue of the Journal of Clinical Investigation.

For the study, researchers compared the heart function of male and female mice with HCM when given either soy diets or milk-protein diets. They also compared the effects of a soy diet and a milk-protein diet on healthy male and female mice without HCM.

They found that the male mice with HCM had significantly improved healthy heart growth and function on the milk-protein diet compared to the HCM male mice on the soy diet, Leinwand said. The female HCM mice did not show the same difference.

Leinwand said that difference in responses between the female mice and the male mice might be related to the fact that the female mice already had high levels of estrogen, so the effect of the estrogens in their soy diet were not as strong as the effect in the male mice.

The reason why soy might adversely affect the HCM mice needs further study since the researchers don't know why it happened, Leinwand said.

Craig T. Basson, director of cardiovascular research in the department of medicine at Weill Medical College of Cornell University in New York City, who wrote a commentary that accompanied the study, said the finding was an important contribution to research looking at how environmental factors influence heart disease.

"We always speculate about how environmental factors influence cardiovascular disease, and this is the first time we've had clear data about the environment," he said. "It opens the door to some very exciting clinical interventions down the line."

Soybean products are often promoted by health advocates because they're a low-fat alternative source of protein, and they possibly reduce the risks of illnesses such as heart disease and cancer. However, many studies on soy are inconclusive and often contradictory.

"We're not trying to say that soy is bad, but that a soy diet can have a significant impact on certain organ systems, including the heart. For the normal, healthy mouse, a soy diet doesn't seem to be either harmful or beneficial, but in the context of this particular disease, soy has a detrimental effect on male mice," Leinwand said.

Interestingly, Leinwand noted, the original intent of their work was to look at how sex differences affect heart disease. As laboratory animals are routinely fed soy diets, and soy contains plant estrogens, the scientists took the mice off the soy and put them on milk-protein diets to better compensate for the differing male and female hormones.

Their discovery of the significant improvement in the heart function of those male mice with HCM who had been switched to the milk-protein diet prompted them to change the focus of their work.

"We were completely surprised," she said.

More information

The Mayo Clinic gives the lowdown on soy.

SOURCES: Leslie A. Leinwand, Ph.D., professor and chairwoman, Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder; Craig T. Basson, M.D., Ph.D., director, Cardiovascular Research, Greenberg Division of Cardiology, Department of Medicine, Weill Medical College of Cornell University, New York City; Jan. 4, 2006, Journal of Clinical Investigation

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