Objective: The soybean has long been an important protein source for approximately 5000 years in Oriental countries. Therefore, soy protein has been widely investigated for its variety of function. However, the side effects had been reported for its close structure of the female hormone, estrogen. In this report, we prepare a new soy peptide derivative and focus on the potency, with special attention to the linkage of peripheral leukocytes in number, emotional hormone and brain blood flow.
Method: Dried powder of soybean-protein or peptide were administered orally at dosage 8g (dry weight) suspension, the blood sample was collected before and after one week at the same hour and served for assessment in order to avoid circadian rhythm.
Results: The cell numbers were up-regulated in the group that had a smaller number of leukocytes before the test, but in the larger number group before the test, they were down-regulated in the soybean-protein and peptide. Therefore, when the number of all subjects were totaled and make mean, indicating no difference. As for the leukocyte subsets, lymphocyte numbers of CD_11b⁺ cells, and CD₅₆⁺ cells significantly increased after ingestion of a single gradient in the soybean-peptide group. On the contrary, only CD₁₉⁺ cell counts were down regulated. In the soybean-peptide group, the adrenalin level in serum, which is regarded as one of the emotional hormones, was down regulated, and another emotional hormone, dopamine, was up regulated. There were no change of CD positive cells and emotional hormones in the soy protein and placebo group. In NIRS, a significant increase in amplitude of all the frequency bands was observed in the peptide group just after 5 min of administration by the sample, peptide.
Conclusion: These results indicate that the soybean peptides can regulate the leukocyte subsets and emotional hormones are also closely related with the change of the brain blood flow in healthy young volunteers.