This study compares the effect of insulin given as a nasal spray with a placebo. Insulin is a chemical messenger (hormone) in the body that controls fat (triglyceride) levels in the blood by controlling the amount of fat made by the liver and gut. Recent research suggests that insulin may work through the brain. The investigators hypothesize that preferential delivery of insulin into the brain, through nasal spray of the hormone, may affect the amount of fats made by the liver and gut.