Food intake is greatly influenced by economic factors. Consequently, neuroeconomics has been identified as a new and important area for understanding the interaction between genotypes and phenotypes related to food intake. A foundational element of economics is choice between alternatives. Changing food choices are a central element in the explanation of the increasing obesity rates in human populations. The purpose of this research is to incorporate the key element of choice into the investigation of food intake and weight-related phenotypes for mice in an operant chamber setting. Using normal mice, and mice with a mutation in the Tubby gene (Tub-Mut) which results in adult onset obesity, this research will investigate different behavioral responses among genotypes, as well as unexplored phenotype outcomes when mice are confronted with a falling price of a high fat food relative to a low fat food. Results for both genotypes indicate that as the price of the high fat food falls, consumption of that food increases, but consumption of the low fat food does not decrease in a compensatory fashion. For both genotypes, weight and body fat percentage increases with decreasing high fat food price, but ghrelin and leptin levels do not significantly change. The Tub-Mut shows a significant increase in the area under the glucose tolerance curve, suggestive of a diabetic state. These results show that accounting for choice in neuroeconomic studies is important to understanding the complex regulation of body weight and diabetes.