Associations between dietary index for gut microbiota and bone health outcomes

Adults who consumed more foods or nutrients that support healthy gut bacteria had fewer fractures, less osteoporosis, and slightly higher bone density. This study suggests that gut-friendly eating habits may be linked to better bone health and should be explored further.

Gut microbiota has been implicated in bone health and may be modulated by habitual diet. However, associations between dietary components influencing gut microbiota composition and/or function-as captured by the dietary index for gut microbiota (DI-GM)-and bone health outcomes have not been previously investigated. The present cross-sectional study was performed to investigate the associations between DI-GM and fracture (primary outcome), as well as osteoporosis and bone mineral density (BMD) at the femoral neck and lumbar spine (secondary outcomes).

Data from 9385 adults aged ≥ 20 years in the National Health and Nutrition Examination Survey (NHANES) 2009-2020 were analyzed. DI-GM scores (range: 0-13) were calculated from two 24-h dietary recalls based on the intake of microbiota-relevant dietary components, including beneficial foods such as fiber-rich plants and fermented dairy products, and unfavorable components such as red and processed meats, refined grains, and high-fat diets. Higher scores reflected more microbiota-supportive diets. Fracture history and osteoporosis status were self-reported, with osteoporosis additionally identified using femoral neck BMD. BMD was measured at the femoral neck and lumbar spine using dual-energy X-ray absorptiometry. Multivariable regression models assessed associations between DI-GM and each bone health outcome, adjusting for relevant covariates.

Each 1-unit increase in DI-GM was associated with lower odds of fracture (OR = 0.90; 95% CI: 0.87-0.93) and osteoporosis (OR = 0.94; 95% CI: 0.92-0.96), with consistent associations across fracture sites and sexes. DI-GM was positively associated with femoral neck BMD (β for each 1-unit increase = 0.003 g/cm²; 95% CI: 0.001-0.005), particularly among men. No association was observed with lumbar spine BMD in the overall (β for each 1-unit increase = -0.001; 95% CI: -0.004 to 0.001) or sex-stratified analyses.

In this nationally representative sample of U.S. adults, greater adherence to a dietary pattern characterized by microbiota-relevant components, as reflected by higher DI-GM scores, was associated with lower prevalence of fracture and osteoporosis, and modestly higher femoral neck BMD. These findings suggest a potential link between diet-microbiota interactions and skeletal health, which warrants further investigations in longitudinal studies.