Brown Adipose Tissue as Nutrient Buffer Through Diet Induced Thermogenesis

In this prospective interventional study healthy individuals will be screened for presence of active BAT: Maximal BAT activity will be achieved by a mild cold stimulus over 2 hous and quantified by 18F-FDG-PET/CT 30 min after injection of 75 MBq of 18F-FDG. Individuals with FDG-PET positive BAT will be included as BAT-positive subjects (n=15) and individuals with absence of FDG-positive BAT will be included as BAT-negative subjects (n=15) and then take part in three study visits in random order. During the study visits participants will consume a standardized isocaloric liquid meal consisting of A) glucose (OGTT) B) fat and C) protein. Energy expenditure will be measured by indirect calorimetry before as well as hourly after the meal for 5 hours. Blood samples will be taken before and at 30 minute intervals after the meal for 5 hours for analysis of blood glucose, triglycerides, FAAs, representative amino acids, insulin and noradrenaline. Subjects will undergo ultrasound-guided biopsy of the supraclavicular fat depot in the fasting state and after one of the test meals so that biopsies from 5 individuals in each group after each test meal will be obtained.