Regulation of FGF21 by Nutritional Challenges

The purpose of this study is to examine how acute nutritional challenges affect levels of several proteins involved in metabolism. These proteins will be measured in blood and fat tissue. This study will have several aims. One aim is to examine the effect of 72 hours of fasting on fibroblast growth factor-21 (FGF-21) levels. Participants will spend 3 days and nights in the Clinical Research Center at the Beth Israel Deaconess Medical Center in Boston, MA. Daily blood samples will be taken. Two fat samples will be taken prior to and at the end of the fast. A subset of participants will also have two MRIs, one prior to and one at the end of the fast. We will study healthy adults and obese adults with liver-biopsy-diagnosed non-alcoholic fatty liver disease (NAFLD). THIS STUDY ARM IS CURRENTLY NOT RECRUITING Another aim is to examine the effect of low-calorie diet on FGF-21 levels. Subjects will follow a hypocaloric diet that will be designed to achieve 3-5% weight loss. We will enroll participants with liver-biopsy-diagnosed non-alcoholic fatty liver disease. Participants will report weekly to the Clinical Research Center at Beth Israel Deaconess Medical Center for weight measurements. Blood will be drawn before and after the weight loss. Participants will also have an MRI before and after the weight loss. THIS ARM IS CURRENTLY NOT RECRUITING Another aim of the study is to examine the effect of acute ingestion of glucose, fructose, and other sugars on serum FGF21 levels. Subjects in this study will be lean volunteers and individuals with metabolic syndrome. THIS ARM IS CURRENTLY RECRUITING

Participation in this study involves fasting overnight, drinking a sweet beverage, and several blood draws through an IV line. Each subject may drink up to 5 different sweet beverages, separated by 2 weeks.