Male mice carrying the mutation for hypertrophic cardiomyopathy or HCM, were severely affected by the soy diet, showing enlarged heart muscles and eventual heart failure, according to the University of Colorado at Boulder study published in the Journal of Clinical Investigation.

HCM is the leading cause of death in young athletes and affects about one in 500 people. Eighteen genes associated with the disease have been identified, according to University of Colorado professor Leslie Leinwand.

Soy foods and diet supplements are perceived to be a huge health benefit to humans. Consumers spent an estimated US$4.7 billion on them in 2005.

"We were shocked by the results," said Leinwand, noting that when the mice in the study were switched to a diet of a milk protein their condition improved markedly.

Female mice carrying the mutation for HCM were relatively unaffected by the soy diet, according to the study.

That led the Colorado research team to believe that heart deterioration in male mice was due at least in part to plant-based estrogens in the soy food diet.

"To our knowledge this is the first report of significant differences in cardiac muscle adaptation due to dietary manipulation," researchers wrote.

Leinwand said: "I don't think normal, healthy people should be alarmed by the results of this study.

"But we are seeing more cautionary reactions from the medical community in recent years regarding the ingestion of huge quantities of dietary supplements, including soy phytoestrogens." -- Reuters