Study co-author Melissa Melby, a medical anthropology professor at the University of Delaware, reviewed 19 previous studies that examined more than 1,200 women.
The effectiveness of soy in alleviating hot flashes has been inconclusive -- some studies suggested soy to be beneficial and others suggested is was not -- but much of the discrepancy was due to small sample sizes and inconsistent methodology, Melby said.
"When you combine them all, we've found the overall effect is still positive," Melby said in a statement.
The study published in Menopause: The Journal of the North American Menopause Association found ingesting at least 54 milligrams of soy isoflavones daily -- about two glasses (16 ounce) of soy milk or 7 ounces of tofu -- for six weeks to a year reduces menopause hot flash frequency by 20.6 percent and severity by 26 percent, compared to a placebo,
The total reduction in frequency and severity might be even greater due to the placebo effect, Melby said.
In longer duration studies of 12 weeks or more, the decrease in hot flash frequency was approximately threefold greater than in shorter-duration trials, Melby added.