Lead author Dr. Victor Henderson, professor of health research and policy, and of neurology and neurological sciences, at Stanford University, said the findings from the 2.5-year study in middle-aged and older women was larger and longer than any previous trials on soy use.
"There were no large effects on overall cognition one way or another," Henderson said in a statement.
Henderson and colleagues conducted the National Institutes of Health-sponsored Women's Isoflavone Soy Health Trial from 2004 to 2008 to determine the effect of soy isoflavones on cognition.
During the study, 350 healthy women ages 45-92 were randomized to receive daily 25 grams of isoflavone-rich soy protein -- a dose comparable to that of traditional Asian diets -- or a placebo. A battery of neuropsychological tests was given to the participants at the start of the study and again 2.5 years later.
The study, published in the journal Neurology, found no significant differences in overall mental abilities.
The work is not meant discourage women who consume soy for other purposes, Henderson said.
"If a woman enjoys eating soy and if there may be other health benefits, she should keep doing what she's doing," Henderson said.