Missing evidence for the effect one-week phytoestrogen-rich diet on mental rotation in two dimensions.

INTRODUCTION: It is well known that men outperform women in tests of spatial cognition, such as mental rotation, and that performance in these tasks is influenced by sexual hormones. Phytoestrogens are plant substances chemically similar to estradiol, capable of binding estrogen receptors. In a previous study, one-week phytoestrogen-rich diet improved performance in mental rotation in women, but it remained unclear whether this was due to direct binding of phytoestrogens to estrogen receptors or by modulating testosterone blood levels.

OBJECTIVES: We investigated whether one week consumption of phytoestrogens will equally affect performance in mental rotation in women and men. We expected improved performance in women, but unchanged skill in men, if the effects were mediated by changes of testosterone level. On the other hand, direct modulation of estrogen receptors should yield comparable improvement in both genders.

METHODS: Thirty-six healthy adult young volunteers (16 females) were divided into the control and soy groups. During 7 consecutive days, in addition to their usual diet, subjects in the soy group consumed a daily dose of 2 g of soybeans per kilogram body weight (about 170 mg/kg of isoflavones). The control group members stayed on their usual diet. The subjects were tested on mental rotation of letters and digits at the baseline and after 7 days of soy consumption.

RESULTS: Consumption of soy had no influence on performance in the mental rotation task. For the intermediate stimulus rotation angle (60 deg), irrespective of soy intake, improvement of response latencies was greater in women than in men.

CONCLUSION: The results indicate that soy phytoestrogens have little impact on mental rotation skill. The findings also suggest that women, in contrast to men, more readily engage memory mechanisms to solve the mental rotation task.