Activation of Brain Centers by Short-term Walnut Consumption in Obesity

The purposes of the study are: * Study Aim 1. To assess the mechanisms underlying the biological effects of short-term walnut consumption on appetite with functional magnetic resonance imaging (fMRI) and assessing neurocognitive function/memory * Study Aim 2. To investigate the effects of walnut consumption (48g per day over 5 days) on appetite and satiety by analyzing molecules which regulate energy homeostasis such as adipokines, as well as resting metabolic rate which measures energy expenditure. * Study Aim 3. To investigate the effects of walnuts (48g per day over 5 days) on insulin resistance, lipids, and inflammatory markers in obesity as well as the effect of walnuts when consumed as part of a mixed meal, on glucose excursions, insulin secretion and the excretion of gut peptides and free fatty acids.