DESCRIPTION (taken from the application) The long-term aim of the investigator is to further better understanding of the role-of insulin resistance in body weight maintenance both in the obese and in the non-obese individual, ethnic differences and how its effects could be remedied. Obesity is wide spread in the U.S. and is known to be associated with many chronic diseases including diabetes. Hyperinsulinemia and insulin resistance normally precedes diabetes. The relationship between insulin resistance and body weight maintenance in the obese state is controversial. Insulin resistance is proposed to be an adaptive mechanism against further weight gain. However, 25 percent of non-obese individuals are insulin resistant, and could be considered predisposed to diabetes. To be both diabetic and insulin resistant would significantly increase one's risk to chronic diseases. This study will investigate whether non-obese individuals, with insulin resistance, are protected against obesity. The specific aims are: (a) to determine whether 24 hour-total and -dietary fat oxidation after consuming low and high fat maintenance meals, are higher in non-obese insulin resistant subjects compared to non-obese insulin sensitive subjects; (b) to determine the effect of 25 percent overfeeding on total and dietary fat oxidation in the two groups. Whole-body indirect calorimetry and 13C stable isotope ratio mass spectrometry will be used in this study. The topic of this study is important because it impacts a significant proportion of the U.S. population. The investigator does not have a major grant and the awarding of this grant will help him to generate the necessary data to allow him to apply for such a grant. This will be a significant burst to his career development.