Increased aggressive behavior and decreased affiliative behavior in adult male monkeys after long-term consumption of diets rich in soy protein and isoflavones

• Published in: Hormones and behavior 2004-04, Vol.45 (4), p.278-284
• Main Authors: Simon, Neal G, Kaplan, Jay R, Hu, Shan, Register, Thomas C, Adams, Michael R
• Format: Article
• Language: English
• Subjects: Aggression; Aggression - drug effects; Androgen; Animal ethology; Animal Feed; Animal Nutritional Physiological Phenomena; Animals; Behavioral psychophysiology; Biological and medical sciences; Estrogen; Estrogen Antagonists - administration & dosage; Fundamental and applied biological sciences. Psychology; Hormones and behavior; Isoflavones - administration & dosage; Macaca fascicularis; Macaca fascicularis - physiology; Macaca fascicularis - psychology; Male; Mammalia; Monkeys; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Social Behavior; Soy isoflavones; Soy protein; Soybean Proteins - administration & dosage; Time Factors; Vertebrata
• ISSN: 0018-506X; 1095-6867
• DOI: 10.1016/j.yhbeh.2003.12.005

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.