ABSTRACT The reinforcing value of food, or how hard someone will work to gain access to a specific food,1 is one potential mechanism for weight gain and obesity in children and adults. The reinforcing value of food is cross-sectionally related to obesity in infants,2 children3 and adults,4 and prospectively related to weight gain in children,5 adolescents6 and adults.7 While food reinforcement predicts weight gain, not everyone high in food reinforcement gains weight. One potential protective factor against weight gain is a strong reinforcing value for alternatives to food.4 Lean children find alternatives to food more reinforcing than food, while obese children find food more reinforcing than alternatives.3 Environments in which children grow up differ in terms of access to a variety of alternative reinforcers, such as reading8 and musical instruments.9 The lack of access to alternatives to food reinforcers may be a particular concern for children who grow up in families with low socioeconomic status (SES), who are at increased risk for becoming obese.10-12 We have shown in adults that the relative reinforcing value of food mediates the relationship between educational level or income level and BMI in adults.13 The overall goal of this grant is to study individual differences in food and alternatives to food reinforcement in the home environment as risk and protective factors for child weight gain. We will study 230 6- 9 year-old children who vary in food reinforcement, parental education and alternatives to food reinforcement, and carefully assess the home environment and leisure time activities. Specific aims are to test the hypotheses that the independent effects of food reinforcement and alternative reinforcers, and the relative balance of food reinforcement to alternative reinforcers, predicts weight gain (Specific Aim 1), that a home environment with opportunities for participation in, enjoyment of and access to a variety of leisure and physical activities is related to high reinforcing value of alternatives to food (Specific Aim 2), that a home environment with greater availability of unhealthy foods is related to high reinforcing value of food (Specific Aim 3), that the relative reinforcing value of food mediates the relationship between low parental education and increased risk of obesity in children (Specific Aim 4), and that parental relative reinforcing value of food predicts child relative reinforcing value of food (Specific Aim 5).