Gut microbiota alterations associated with obesity and impact of a weight-loss intervention based on a hypocaloric balanced diet

In the present study, the gut microbiota (GM) from overweight/obese patients (OB) of Sardinian origin, was characterized and compared to normal-weight controls from the same geographical area (NW), matched for sex, age and smoking status. Fecal samples were analyzed by Illumina MiSeq sequencing of the 16S rRNA gene. The gut microbial community of OB patients exhibited a significant decrease in the relative abundance of several Bacteroidetes taxa (i.e. Flavobacteriaceae, Porphyromonadaceae, Sphingobacteriaceae, Flavobacterium, Bacteroides spp.) when compared to NW; instead several Firmicutes taxa were significantly increased in the same subjects (Lachnospiraceae, Gemellaceae, Streptococcaceae, Gemella, Megamonas, Mitsuokella, Streptococcus, Eubacterium spp., Ruminococcus spp., Megamonas spp., Megasphaera spp. and Veillonella spp.). Correlation analysis indicated that body fatness and waist circumference negatively correlated with Bacteroidetes taxa, while Firmicutes taxa positively correlated with body fat and negatively correlated with muscle mass and/or physical activity level. Furthermore, the relative abundance of several bacterial taxa belonging to Enterobacteriaceae family, known to exhibit endotoxic activity, was increased in the OB group compared to NW. A secondary aim of the study was to evaluate the impact of a moderately hypocaloric Mediterranean diet, lasted three months, on the GM of OB patients. After nutritional intervention, patients presented a reduction in body weight and fat mass, along with changes in the relative abundance of many microbial patterns. In fact, an increase in the abundance of several Bacteroidetes taxa (i.e., Sphingobacteriaceae, Sphingobacterium, Bacteroides spp.) and a depletion of many Firmicutes taxa (i.e., Lachnospiraceae members, Ruminococcaceae, Veillonellaceae, Megamonas, Ruminococcus) were observed. In addition, the genus Sutterella, within Proteobacteria, decreased after the intervention. The present study extends our knowledge of the GM profiles in OB, highlighting the potential benefit of moderate caloric restriction in counteracting the gut dysbiosis.