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.
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