Systemic inflammation index mediated the associations between dietary intake for gut microbiota and muscle mass: a cross-sectional study.

OBJECTIVE: The associations between a diet that associated with maintaining a healthy gut microbiota and muscle mass, as well as the role of inflammation in these associations, remain unclear. This study aimed to examine the associations between the dietary index for gut microbiota (DI-GM) and muscle mass, and to explore whether the systemic inflammation index (SII) mediates these associations. METHODS: A total of 6,908 participants, aged 20 to 59 years, from the 2010-2018 cycles of the National Health and Nutrition Examination Survey, were included in this cross-sectional study. The DI-GM was calculated based on the dietary intake of 13 foods or nutrients, with a higher score indicating a diet associated with a healthier gut microbiota. Muscle mass was assessed using the skeletal muscle mass index (SMI), which was calculated by dividing the appendicular lean mass by the square of height. The SII was calculated by multiplying the platelet count and neutrophil count, and then dividing by the lymphocyte count. Weighted multivariable linear regression models were used to examine the associations between DI-GM and SMI. Mediation analysis was performed to investigate the role of SII in mediating the association between DI-GM and SMI. RESULTS: Each 1-point increase in DI-GM was associated with a 0.03 (95% CI: 0.01 to 0.04) increase in SMI. The stratified analyses revealed that, with the exception of alcohol consumption, age, gender, race, marital status, education level, income level, smoking status, physical activity, BMI categories, and the history of hypertension, diabetes, cardiovascular disease, or cancer did not modify the association between DI-GM and SMI (P values for all interaction terms >0.05). The positive association between DI-GM and SMI were more pronounced among non-drinkers when comparing the highest quintile to the lowest quintile (β: 0.29; 95% CI: 0.14 to 0.43). SII partially mediated the associations between DI-GM and SMI, with a mediation proportion of 11.6%. CONCLUSION: DI-GM was positively associated SMI, with SII partially mediating this association. These findings suggested that a diet associated with maintaining a healthy gut microbiota may help prevent muscle mass loss by reducing systemic inflammation.