MONDAY, Aug. 20, 2001 (HealthDayNews) -- Eat tofu before heart surgery and you may have fewer complications afterwards. New animal studies find the estrogen-like properties in soy may reduce the risk of some common complications following open-heart surgery.
"We have already shown in previous studies that estrogen can protect the heart during open heart surgery. Now we have shown the same positive effects can result from phytoestrogens that are found in soy," says study co-author David Gross, professor of physiology and head of veterinary biosciences at the University of Illinois College of Veterinary Medicine.
Phytoestrogens are plant substances that act like a very weak natural estrogen in humans.
Gross says the goal of the research is to figure out how these substances protect the heart so that drugs can be developed to promote estrogen's positive effects without its harmful effects on other parts of the body. Estrogens are linked to an increase in breast and uterine cancer.
"The problem with soy, as with any natural substance, is it is hard to control the exact effects you are going to get, whereas a medication can be developed to produce consistent results that are targeted at a certain area," says Gross.
Cardiologists say the research is promising but wonder if the animal results will apply to humans.
"I think it's valuable research that is on the right track, but unfortunately, there are factors in the study which apply to animals but don't necessarily apply to open-heart surgery in humans. So right now, there is just a little too big a leap of faith to say eating soy is going to protect your heart during surgery," says Dr. Edmund Herrold, associate professor of medicine at Weill Medical College of Cornell University.
The study involved five groups of female rats, all with their ovaries removed to shut down estrogen production. Beginning three months before heart surgery, the first group of rats was fed a diet high in soy protein and isoflavone, a phytoestrogenic component of soy similar to human estrogen. The second group was fed the same diet but was given a drug to block the effects of estrogen. The third group ate a diet high in soy but low in phytoestrogens. The fourth group ate a diet free of all phytoestrogens, while the fifth group ate a normal rodent diet containing no soy and no phytoestrogens.
After three months, a procedure mimicking open-heart surgery in humans was performed on the rats: The hearts were removed, blood flow was halted for 30 minutes, followed by an infusion of a blood substitute. The hearts were then restarted and allowed to function for two hours.
Rats who ate soy high in phytoestrogens fared the best, with a much reduced rate of post-operative complications, including swelling of heart tissue. They also had healthier levels of overall coronary blood flow.
The other four groups suffered specific damage to the heart similar to humans who undergo open-heart surgery, says Gross.
"It was clear that the rats, which had the protection of the high-phytoestrogens-soy diet did better, which reinforces our earlier studies showing estrogen's protective effects on the heart during and after surgery," says Gross.
The research will be published in the upcoming issue of the American Journal of Physiology: Heart and Circulatory Physiology.
Herrold points out that at least some of the criteria used in the study don't carry over from rodent to man.
"During open-heart surgery on humans, the heart is likely to be stopped for a lot longer than 30 minutes, and when the heart is restarted, it is not with a blood substitute, but with blood, usually the patients own blood, if possible," says Herrold.
In addition, he says the two hours that the rats' hearts were studied post operatively is not enough to document any lasting results.
"We don't know if they would revert to the same problems as the other rats in the group after the two hours or develop even worse problems. There's no way of knowing right now," says Herrold.
However, he says, "Even if the soy/estrogen therapy offered a slight boost in recovery in the hours directly following surgery, it would be well worth the dietary efforts."
Gross and his team say they plan to expand their studies to answer questions that Herrold poses, and, they say they are confident the answers eventually will translate into saving human lives.
What To Do
Researchers say it's still too early to tell if a diet high in soy-rich phytoestrogens can make a difference in your life. However, experts agree that more soy in your diet can help on many levels, and that, right now, there's little evidence of any potential for harm.
For more information on phytoestrogens, including links between soy and estrogen, visit The American Family Physician.
To learn more about foods high in phytoestrogens other than soy, visit Healthcare Reality Check.
Curious to see how much phytoestrogen is in your food? Check this U.S. Department of Agriculture site. And if you're thinking about putting more soy in your diet, check the SoyFoods Directory.
