CD163 is a membrane bound receptor primary expressed in monocytes and macrophages. A soluble variant of CD163 (sCD163) is present in plasma and is elevated in pathological condition activating the monocyte-macrophage system. Recently sCD163 is associated with various inflammatory conditions, ex. adipose tissue inflammation and very recently to be a rather strong predictor of the development of type 2-diabetes. Only a subset of obese individuals develops insulin resistance, type 2-diabetes and related diseases. These healthy obese subjects are characterized of less adipose tissue inflammation and less insulin resistance as compared to unhealthy obese individuals. Consequently it would be of great importance to develop markers that could discriminate between healthy and unhealthy obese subjects. Aim: To investigate whether macrophage CD163 is involved in adipose tissue inflammation in obesity and thereby to the metabolic complications of metabolic syndrome. To investigate how sCD163 is regulated by metabolic factors such as obesity, fat distribution, weight loss and diet. Methods: Intervention study. 45 morbidly obese subject approved to gastric by-pass. Blood samples, MR-spectroscopy, DXA, weight control and fat biopsy are taken before and 12 month after surgery. Correlations studies: to investigate the influence of diet and weight loss on CD163 and sCD163. Perspective: To study the role of macrophages infiltration and activation for adipose tissue inflammation and to determine whether the macrophage marker, s-CD163, together with other markers will be able better to identify obese individuals who are at increased risk for developing complications such as diabetes