In this application, the investigators propose to systematically assess the effects of two diets enriched in either saturated or unsaturated fatty acids and determine the cellular and molecular mechanisms of the apparent increase in insulin sensitivity. The investigators hypothesize that individuals will 'adapt' to the different diets and the investigators will be able to generate predictive alterations in gene expression and metabolites that underlie the alterations in metabolism. In parallel, the investigators will test the ability of these different diets to affect the release of gastrointestinal hormones that may be critical to modulation of appetite.