Short-term soybean intake and its effect on steroid sex hormones and cognitive abilities

ObjectiveTo observe the effects of short-term soybean consumption on cognitive spatial abilities and changes in sex endocrine net in both genders.DesignShort-term prospective intervention study.SettingAcademic medical center.Patient(s)Fifty-four healthy females and 32 healthy males (18 – 25 y of age).Intervention(s)Volunteers were asked to eat 2 g/kg per day of soybeans during 1 week. Saliva and plasma samples were taken, and psychometric tests were performed on the 1st (before soybean intake), 7th (after soybean intake), and 14th days (after washout period) of the study.Main Outcome Measure(s)Salivary T and plasma E2 were measured. Mental rotation (MR) and spatial visualization (SV) tests were performed on the days of sampling.Result(s)Soybean intake did not change salivary T and plasma E2 levels in men. During the washout period, both parameters have shown a tendency to rise. The effect of soybean intake on hormonal parameters in men was, however, dependent on the basal T levels. In women, salivary T as well as plasma E2 levels showed a tendency toward a decline after soybean intake (the decrease in E2 was statistically significant) and to increase back toward basal levels during the washout period. Both males and females statistically significantly improved in MR and SV after soybean intake. During the washout period, both genders further improved their results in MR but not in SV.Conclusion(s)Short-term soybean consumption alters the concentrations of salivary T and plasma E2 in both men and women. Spatial abilities appear to be improved by short-term soybean intake, but the exact mechanisms require further study.