Increased aggressive behavior and decreased affiliative behavior in adult male monkeys after long-term consumption of diets rich in soy protein and isoflavones.
Estrogen produced by aromatization of gonadal androgen has an important facilitative role in male-typical aggressive behavior that is mediated through its interaction with estrogen receptors (ER) in the brain. Isoflavones found in soybeans and soy-based dietary supplements bind ER and have dose- and tissue-dependent effects on estrogen-mediated responses. Yet, effects of isoflavone-rich diets on social and aggressive behavior have not been studied. We studied the effects of long-term (15 months) consumption of diets rich in soy isoflavones on spontaneous social behavior among adult male cynomolgus macaques (Macaca fascicularis) (n = 44) living in nine stable social groups. There were three experimental conditions which differed only by the source of dietary protein: casein and lactalbumin (no isoflavones), soy protein isolate containing 0.94 mg isoflavones/g protein, and soy protein isolate containing 1.88 mg isoflavones/g protein. In the monkeys fed the higher amount of isoflavones, frequencies of intense aggressive (67% higher) and submissive (203% higher) behavior were elevated relative to monkeys fed the control diet (P's < 0.05). In addition, the proportion of time spent by these monkeys in physical contact with other monkeys was reduced by 68%, time spent in proximity to other monkeys was reduced 50%, and time spent alone was increased 30% (P's < 0.02). There were no effects of treatment on serum testosterone or estradiol concentrations or the response of plasma testosterone to exogenous gonadotropin-releasing hormone (GnRH). The results indicate that long-term consumption of a diet rich in soy isoflavones can have marked influences on patterns of aggressive and social behavior.
Simon
Neal G
NG
Department of Biological Sciences, Lehigh University, Bethlehem, PA 18015, USA.
Kaplan
Jay R
JR
Hu
Shan
S
Register
Thomas C
TC
Adams
Michael R
MR
D000374:Aggression / Q000187:drug effects*; D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D004965:Estrogen Antagonists / Q000008:administration & dosage; D007529:Isoflavones / Q000008:administration & dosage*; D008252:Macaca fascicularis / Q000502:physiology* / Q000523:psychology; D008297:Male; D012919:Social Behavior; D030262:Soybean Proteins / Q000008:administration & dosage*; D013997:Time Factors
D004965:Estrogen Antagonists; D007529:Isoflavones; D030262:Soybean Proteins