Dietary and metabolic effects on rhesus social behavior: protein and protein-calorie malnutrition.

Forty-seven monkeys were fed 1 of 8 diets between the ages of 1 and 7 months containing full-, half-, or quarter-strength protein or protein and calories using either casein or soy protein. While on the diet, malnourished infants were inactive both socially and nonsocially. When returned to a normal diet, previously malnourished subjects were more agonistic towards familiar peers but more friendly and less agonistic when later paired with unfamiliar monkeys. The data suggest that short periods of early severe malnutrition may protect the individual against adverse social conditions (e.g., isolation) and delay the development of normal social skills.