Background: The gut microbiota plays an important role in human metabolism; previous studies suggest that the imbalance can cause a metabolic endotoxemia that may be linked to weight gain and insulin resistance. The purpose of this study was to investigate the relationship between the gut microbiota composition, the lipopolysaccharide levels and the metabolic profile in obese and normal-weight young subjects. Methods: We studied 32 obese (BMI >= 30 kg/m(2)) and 32 normal-weight subjects (BMI = 18.5-24.9 kg/m(2)), aged 18-25 years. Quantification of intestinal bacteria was performed by real-time PCR. Endotoxin units were determined with the test QCL-1000, and biochemical profile was performed under a standard protocol of Spinreact. Results: Obese individuals had a BMI of 34.5 (32.9-36.45) kg/m(2), increased triglycerides (123 vs. 70 mg/dl), total cholesterol (168 vs. 142 mg/dl), and LDL-cholesterol (114 vs. 96.5 mg/dl). In obese subjects body temperature was higher than in normal-weight subjects. We found a greater number of Clostridum leptum and Lactobacillus (p < 0.001) and lower numbers of Prevotella and Escherichia coli (p < 0.001) in the obese group. A decrease of E. coli was associated with an increased risk of lipopolysaccharide levels ranging from 1 to 1.3 EU/ml. A positive correlation was found between serum lipopolysaccharides and BMI (r = 0.46, p = 0.008), triglyceride levels (r = 0.44, p = 0.011) as well as waist circumference (r = 0.34, p = 0.040), being more evident in young obese females. Conclusion: Subclinical metabolic endotoxemia determined by serum concentration of lipopolysaccharides was related to the smallest amount of E. coli, high triglyceride levels, and central adiposity in obese young persons. (C) 2016 S. Karger GmbH, Freiburg