Individuals have a significant capacity to adapt to different environments by changing their core metabolic pathways. This adaptation is especially important in regards to diet. Epidemiological research over the last several decades have shown that diets high in saturated fats have a greater ability to cause insulin resistance and the 'metabolic syndrome' while diets low in saturated fats (or a so called 'Mediterranean Diet), reduces the risk for cardiovascular disease. In humans, experimental diets high in unsaturated fats, as compared to high carbohydrate or high saturated fat diets, result in increased insulin sensitivity and improved lipid profiles.

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.

Inclusion Criteria:

• Premenopausal females with BMI range of 25-32 kg/m2

Exclusion Criteria:

• Evidence of metabolic or cardiovascular disease, Fasting plasma glucose concentration > 125mg/dl, Abnormal EKG, Hyperlipidemia (plasma triglyceride concentration > 150mg/dl), Pregnancy, Hematocrit <34%