The association between a newly proposed gut microbiota dietary index and obesity among U.S. adults: a cross-sectional analysis based on NHANES 1999–2020

Abstract Objective Obesity is linked to gut microbiota dysbiosis, and diet is a key determinant influencing the gut microbiome. This study examined the association between a newly proposed Dietary Index for Gut Microbiota (DI-GM) and obesity in the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2020. Methods A total of 41,159 adults aged ≥ 20 years were included, with 15,327 individuals classified as obese (BMI ≥ 30 kg/m²) and 25,832 as living without obesity. DI-GM comprises 13 components deemed either beneficial or unfavorable to the gut microbiome, yielding a total score ranging from 0 to 13. Weighted logistic regression assessed the relationship between DI-GM (continuous and categorical) and obesity, adjusting for demographic and lifestyle factors plus comorbidities. Restricted cubic spline, stratified analyses, multiple imputation, and propensity score matching were also performed. Results Participants with obesity had a significantly lower mean DI-GM score than those without obesity (4.32 vs. 4.65, P < 0.001). Each 1-point increase in DI-GM was associated with 13% lower obesity odds (OR = 0.87, 95% CI: 0.85–0.88) in the crude model, remaining robust (OR = 0.88, 95% CI: 0.87–0.90, P < 0.001) after full adjustment. Higher DI-GM scores were linearly linked to lower odds of obesity, supported by multiple imputation and propensity score matching (P < 0.001). Conclusion In this nationally representative U.S. population, a more microbiota-oriented diet, as proxied by higher DI-GM scores, was independently associated with lower odds of obesity. Prospective and randomized trials are warranted to verify causality and investigate underlying mechanisms.