In Reply

We thank our correspondents for their interest in our article (1) and for their valuable additional points. We did not explain possible causes for the development of obesity in our article. Whereas the body height of a person is 80–90% genetically determined, this rate is 70% for obesity. About 30% are the result of epigenetic influences and environmental factors (diet, lifestyle, medical interventions) and can therefore be changed by means of targeted interventions (2). The microbiome, as mentioned by Dr Alexopoulos, is a particularly interesting piece of the mosaic in obesity development, because it is affected by external influences, such as diet or obesity, on the one hand, and it is determined by an individual‘s genetic background, on the other hand (2).

In our article we described the fundamental mechanisms of action of obesity surgery. We aimed to explain that the long-term effect mostly does not depend on restriction or malabsorption. By mentioning the bile acid metabolism, Dr Alexopoulos pointed out another element of postbariatric changes. Only in recent years has it become clear that the receptors he described also have a steering function in the glucose and lipid metabolism and energy regulation (3). The presumed large impact that the bile acid metabolism has in postbariatric metabolic changes was shown in a mouse model, in which a direct diversion of bile into the ileum triggered a similar metabolic effect as a Roux-en-Y gastric bypass (4).

Protein deficiency is the most common macro nutrient deficiency after obesity surgery. Also in our experience, reaching the required protein volume is difficult especially in the early postoperative period. Therefore, the suggestion by Prof Weck, Dr Ott, and Dr Becker—to supplement protein using protein powder is practical and helpful, and our center handles things exactly in this way. The recommendations of the German guidelines on protein supplementation are based on the recommendations of US guidelines. These recommend 60 g/day or up to1.5 g/kg of ideal body weight after obesity surgery (5). Greater volumes of supplementation of up to 2.1 g/kg should be adjusted individually. The grade of this recommendation is low, as mostly no evidence is available (5).

Because of bone density loss, patients after obesity surgery have a 1.2 times increased risk of fractures than patients in the control group with obesity without surgical intervention (5). Prof Weck, Dr Ott, and Dr Becker are completely right to point out the required monitoring of parathormone. According to the German S3 guideline, this should be checked after three, six, and 12 months, and at yearly intervals after. Bone density measurement after two years is recommended as optional in the German as well as in the US guideline because of low-level evidence (5).