Background The gut microbiome impacts human health through various mechanisms and is involved in the development of a range of non-communicable diseases. Diet is a well-known factor influencing microbe-host interaction in health and disease. However, very few findings are based on large-scale analysis using population-based studies. Our aim was to investigate the cross-sectional relationship between habitual dietary intake and gut microbiota structure in the Cooperative Health Research in the Region of Augsburg (KORA) FF4 study. Results Fecal microbiota was analyzed using 16S rRNA gene amplicon sequencing. Latent Dirichlet allocation (LDA) was applied to samples from 1992 participants to identify 20 microbial subgroups within the study population. Each participant’s gut microbiota was subsequently described by a unique composition of these 20 subgroups. Associations between habitual dietary intake, assessed via repeated 24-h food lists and a Food Frequency Questionnaire, and the 20 subgroups, as well as between prevalence of metabolic diseases/risk factors and the subgroups, were assessed with multivariate-adjusted Dirichlet regression models. After adjustment for multiple testing, eight of 20 microbial subgroups were significantly associated with habitual diet, while nine of 20 microbial subgroups were associated with the prevalence of one or more metabolic diseases/risk factors. Subgroups 5 (Faecalibacterium, Lachnospiracea incertae sedis, Gemmiger, Roseburia) and 14 (Coprococcus, Bacteroides, Faecalibacterium, Ruminococcus) were particularly strongly associated with diet. For example, participants with a high probability for subgroup 5 were characterized by a higher Alternate Healthy Eating Index and Mediterranean Diet Score and a higher intake of food items such as fruits, vegetables, legumes, and whole grains, while participants with prevalent type 2 diabetes mellitus were characterized by a lower probability for subgroup 5. Conclusions The associations between habitual diet, metabolic diseases, and microbial subgroups identified in this analysis not only expand upon current knowledge of diet-microbiota-disease relationships, but also indicate the possibility of certain microbial groups to be modulated by dietary intervention, with the potential of impacting human health. Additionally, LDA appears to be a powerful tool for interpreting latent structures of the human gut microbiota. However, the subgroups and associations observed in this analysis need to be replicated in further studies.

Objective: To pool and analyse, according to standardized criteria and using harmonized variables, the existing databases of surveys on childhood overweight and obesity carried out from 1995 to 2005 in different European countries by research groups participating in the IDEFICS project. Methods: Detailed information from seven surveys in five European countries was collected. A common database was built after harmonization of the single studies regarding sample size and age distribution. Variables were critically reviewed and harmonized according to a common protocol. On the pooled database, descriptive comparative analyses on the prevalence of overweight/obesity and association analyses of these conditions with perinatal, parental and environmental factors were performed. Results: Starting from total number of 74 871 children, data of 18 626 children were included in the common database (Belgium, n ¼ 1766; Cyprus, n ¼ 5540; Estonia, n ¼ 583; Italy, n ¼ 4480 and Sweden, n ¼ 6257). After the exclusion of children outside the defined age ranges (4-5 and 9-11 years), the analysis was conducted on 1738 younger and 12 923 older children. Relevant differences in the prevalence of overweight/obesity were observed between countries in both age groups, the highest values being observed in Italy. Age-and gender-related associations between the risk of obesity/overweight and perinatal, parental and environmental factors were observed. An increased risk of high blood pressure in overweight/obese children was consistently observed. Conclusions: The results of this collaborative work of European research centres, although providing potentially useful findings, confirmed that the validity of comparisons between communities depends critically on the comparability of the survey methods. To monitor the current epidemic of childhood obesity and develop appropriate prevention strategies, a coordinated European approach is needed to collect homogeneous sets of epidemiological data.