Certain changes in the composition of gut bacteria may be predictive of the development of obesity and metabolic diseases—and could differ based on sex, according to findings that will be presented by Aranaz et al at the upcoming European Congress of Obesity 2024 in May. Previous studies have demonstrated that gut dysbiosis may influence metabolic health and the risk of certain types of diseases; however, which bacteria may be responsible for the onset of obesity is still unclear. Researchers used the Spanish Obekit study to analyze the fecal metabolome as well as the metagenomic and metabolomic data of 361 participants—65 of whom were a normal weight, 110 of whom had overweight, and 186 of whom had obesity. Two hundred and fifty-one of the participants were women and 110 were men. Researchers categorized the participants into two groups based on their obesity index: low, encompassing participants with a BMI of ≤ 30 kg/m² and women and men with a fat mass percentage of ≤ 25% and ≤ 32% and a waist circumference of ≤ 88 cm and ≤ 102 cm, respectively; and high, encompassing participants with a BMI of > 30 kg/m² and women and men with a fat mass percentage of > 25% and > 32% and a waist circumference of > 88 cm and > 102 cm, respectively. After conducting genetic microbiota profiling, participants in the high obesity index group had lower levels of Christensenella minuta. In men, a higher level of Parabacteroides helcogenes and Campylobacter canadensis signified a higher BMI, fat mass percentage, and waist circumference; in women, Prevotella micans, Prevotella brevis, and Prevotella sacharolitica were correlated with these same characteristics. Additionally, participants in the high obesity index group had variation in the abundance of phospholipids, sphingolipids, and metabolites such as bioactive lipids that contribute to the development of metabolic diseases, diabetes, and vascular complications. The researchers hope their new findings can lead to the development of novel strategies to modify the presence of specific bacteria strains and target obesity. “Our findings reveal how an imbalance in distinct bacterial groups are likely to play an important role in the onset and development of obesity. [T]he species that influence the risk of … obesity appear to be different between the sexes, and interventions to help prevent an obesity-favorable microbiome may need to be different in men and women,” concluded lead study author Paula Aranaz, PhD, of the Centre for Nutrition Research at the University of Navarra in Spain.