A nurse is assessing a 9-month-old infant who has shown minimal weight gain. The parent reports the baby eats less than usual and tires easily during play. Both parents are of average height. Which factor is most likely affecting the infant's growth?

A. Psychosocial environment is incorrect because while a stimulating and supportive environment can influence growth indirectly, the primary concern for minimal weight gain and fatigue in an infant is related to intake and nutritional status rather than parental interaction or emotional factors alone. B. Genetics is incorrect because both parents are of average height, suggesting that hereditary factors are unlikely to explain poor weight gain in this infant. Genetic potential affects height and weight trends but would not typically cause sudden minimal weight gain and fatigue. C. Daycare setting is incorrect because while meal patterns and activity level at daycare could influence intake, the report of decreased appetite and fatigue suggests a direct nutritional or health issue rather than environmental influence alone. D. Nutrition is correct because insufficient caloric or nutrient intake is the most likely cause of poor weight gain, low energy, and fatigue in a 9-month-old. At this age, infants rely on adequate nutrition from breast milk, formula, or complementary foods to support rapid growth and development.