Body Mass Index and Caloric Value of Rewards as Parameters That Modulate Delay-Discounting Rates

In this study, the contribution of the caloric value of primary rewards in conjunction with the body mass index (BMI) of 124 adolescents on delay-discounting rates was examined. Participants were divided into 4 groups according to their BMI: low weight, normal weight, overweight, and obesity. Subsequently, they estimated the subjective value of the following rewards: fruit, fast food, water, soda, and money, with an adjusting-amount procedure with the following delays: 1 day, 1 week, 1 month, 6 months, 1 year, 3 years, and 5 years. Globally, it was found that fast food and soda showed lower discounting rates than fruit, water, and money. It was also found that while the BMI of the participants increased, the discounting rates of fast food and soda decreased, the rates of water increased, and the rates of money decreased and then increased again. Although in previous research it has been found that primary rewards are discounted at a higher rate than conditioned rewards, like money, the results of this study suggest that both caloric level of primary rewards and BMI of the participants are parameters that modulate the delay-discounting rates. In addition, the findings of this study suggest the existence of a continuous process of discounting that runs with BMI, which is a continuous health index. The form of the relation between these continua depends on variables such as the type of reward tested.