July 6, 2004 -- With thousands of studies having been done, soy protein has emerged as one of the most researched foods in science. Even with this much information, studies still show conflicting results on the effects of this much ballyhooed protein.
From tempering menopausal symptoms to reducing the risk of several health problems that plague women following it, some women still turn to soy as an alternative to traditional estrogen therapy.
And yet in the latest study, researchers from the Netherlands find that daily soy supplements did not help preserve a women's thinking ability or bone density. The study also showed no evidence that the supplement provided heart protection by improving women's cholesterol levels following menopause.
Why the sudden departure from previous findings that have supported a beneficial effect from soy, the plant-derived estrogen-like compound? Perhaps because the women studied were between ages 60 and 75 when they started taking soy proteins -- when they may have been too old to reap its reported benefits.
Don't Wait too Long
"Timing is certainly a reasonable explanation as to why we didn't find an effect from soy in the women studied," researcher Sanne Kreijkamp-Kaspers, MD, PhD, tells WebMD.
"We know that immediately after menopause, there's a huge decline in bone loss and that's when [bad] cholesterol levels tend to increase," she says. "It could be that if you give soy before a woman reaches menopause, it is effective at preventing this."
If supplementation begins a decade of so after menopause, it may be too late, she explains.
In her study, published in this week's Journal of the American Medical Association, 200 women received either 25 grams of soy protein each day via a powder that could be mixed with food or beverages or a phony powder package. Each daily dose of soy contained 99 milligrams of isoflavones, such as genisten and diadzein, the most common form of phytoestrogen.
None of the women had ever consumed soy supplements prior to the study, according to Kreijkamp-Kaspers, an epidemiologist at University Medical Center in Utrecht. "Soy is not as popular in the Netherlands as it is in the U.S.," she explains.
No Change After 1 Year
The women were tested at the beginning of the study, and again one year later, on various aspects of their thinking, memory, and reasoning abilities; bone mineral density and cholesterol levels were also tested. These are health issues that worsen following menopause.
During the study period, test scores on health-related issues were virtually identical in both groups of women. This indicated that in this group of women a soy-supplemented diet had no beneficial health effects.
These findings come as no surprise to Mark Messina, PhD, a nationally known soy expert and adjunct associate professor of nutrition at Loma Linda University who is currently revising a book on the health impact of soy protein, which has estrogen-like properties and mimics some of the benefits of hormone replacement therapy, but without some of its risks.
"By the time you reach 60, so much of that estrogen-related bone loss has already occurred that I'm not convinced you can get it back -- with soy or anything else," Messina tells WebMD. "The effect soy might have on cognitive function [such as thinking and memory] is questionable anyway, so I wouldn't expect to see much there. And despite some early studies, more recent research shows that soy's benefit on cholesterol is modest, and it usually seen mostly in those with high cholesterol."
Like Kreijkamp-Kaspers, Messina, who writes a soy newsletter distributed to 70,000 dieticians, suggests that timing could play a role in how much benefit women get from soy-rich foods or supplementation.
"Giving the preliminary data that is encouraging but certainly not definitive, I have no problem telling women that when they hit menopause, they should definitely consider adding some soy or other sources of isoflavones in their diet -- especially if they're concerned about their bones," he says.
What We Know About Soy
Past studies show that regular consumption of soy can reduce hot flushes by as much as 50%. And following menopause, daily soy consumption in the 25-gram per day range has been shown to improve cholesterol levels by about 8%, enough to prompt both the FDA and American Heart Association to tout soy as being heart-healthy. In one study last year, regular soy consumption benefited people with high cholesterol as well as aided their prescription cholesterol-lowering statin drugs. But many critics have said that these studies included only a small number of people and their findings cannot be generalized to the population. Others have said that these studies are of poor quality.
Meanwhile, other studies show that soy supplements at similar amounts in Kreijkamp-Kaspers' study, can keep bones strong -- even after menopause -- and one study even showed that a soy-rich diet could halve a woman's risk of breast cancer following menopause, when it typically skyrockets.
However, Kreijkamp-Kaspers tells WebMD that many of those studies also included premenopausal women, as well as men, or tracked postmenopausal women who may have started taking soy before they reached menopause. "There is very little data that looks at starting soy supplementation only on women after they have already gone through menopause," she says.
But despite her findings, even she isn't suggesting that women shelve the notion that soy can help them. "I certainly wouldn't recommend that women begin taking soy postmenopause," she says. "But if they have started it before menopause and seem to get some benefit from it, there certainly can continue because soy poses no harm that we know of. However, as it relates to preventing several aspects related to aging, the timing of when you start taking soy does seem to play a role."