Gut microbiota composition correlates with changes in body fat content due to weight loss.

Genetics, lifestyle, and dietary habits contribute to metabolic syndrome, but also an altered gut microbiota has been identified. Based on this knowledge it is suggested that host bacterial composition tends to change in response to dietary factors and weight loss. The aim of this study was to identify bacteria affecting host metabolism in obesity during weight loss and to correlate them with changes of the body composition obtained from bioelectrical impedance analysis (BIA). We recruited obese individuals receiving a dietary intervention according DACH (German, Austrian, and Swiss Society of Nutrition) reference values and guidelines for 'prevention and therapy of obesity' of DAG e.V., DDG, DGE e.V., and DGEM e.V. over three months. Faecal microbiota and BIA measurements were conducted at three time points, before, during, and after the intervention. Gut microbiota was analysed on the basis of 16S rDNA with quantitative real time PCR. Additionally, a food frequency questionnaire with questions to nutritional behaviour, lifestyle, and physical activity was administered before intervention. After weight reduction, obese individuals showed a significant increase of total bacterial abundance. The ratio of Firmicutes/Bacteroidetes significantly decreased during intervention. Lactobacilli significantly increased between the first and the second time point. These differences also correlated with differences in weight percentage. During the intervention period Clostridium cluster IV increased significantly between the second and the third time point. In contrast Clostridium cluster XIVa showed a decreased abundance. The dominant butyrate producer, Faecalibacterium prausnitzii, significantly increased as did the abundance of the butyryl-CoA: acetate CoA-transferase gene. Archaea and Akkermansia were significantly more prevalent after weight reduction. Our results show a clear difference in the gut bacterial composition before and after dietary intervention with a rapid change in gut microbial composition after a few weeks, but also indicate that a major shift requires long term dietary treatment.