 Eating a diet high in fat contributes to the development of atherosclerosis hardening of the arteries. Acute fat consumption increases levels of fat in the blood and temporarily reduces the ability of blood vessel to dilate open up to carry additional blood. A similar response is observed during infusion of Intra-Lipid a fat emulsion used for intravenous nutrition. The present study is designed to help us understand the effects of a fat load on blood vessel function. We will measure arterial dilation using non-invasive techniques before and at the end of a 5-hour infusion of Intra-Lipid in healthy subjects. Subjects will then take the approved drug metformin for two weeks and return for repeat studies of endothelial function with Intra-Lipid infusion. We expect that metformin will help preserve the normal function of blood vessels during a fat load. This study will help us understand how fat affects blood vessels and therefore will advance our knowledge of the development of atherosclerosis and potentially lead to improved methods to prevent and treat heart disease. 