Prader-Willi Syndrome Macronutrient Study

The overall objective is to explore the mechanisms by which macronutrients regulate food intake and weight gain in Prader Willi Syndrome (PWS). Previous studies from the investigators' labs suggest that the increased appetite of PWS may be triggered or maintained by an increase in the levels of ghrelin, an appetite-stimulating hormone produced primarily by the stomach. This study will compare the effects of low carbohydrate diet versus low fat diet on levels of ghrelin, appetite suppressing hormones and markers of insulin sensitivity in patients with PWS. The investigators hypothesize that the low carbohydrate diet will suppress plasma active ghrelin and increase appetite-suppressing hormones to a greater degree and for longer duration than the low fat diet and will thereby reduce hyperphagia and increase satiety. The investigators also hypothesize that the low carb diet will improve hormonal and metabolic markers (fatty acids, amino acids and organic acids) of insulin sensitivity and inflammatory cytokine profiles of children with PWS.