Modified cardiometabolic index outperforms conventional indices in discriminating relative muscle loss: a cross-sectional analysis of NHANES 2011-2018.

Higher MCMI was strongly associated with greater odds of relative muscle loss in survey-weighted analyses.

• Per 1-unit increase in MCMI: OR = 2.68, 95% CI 2.21–3.25
• Participants in the highest MCMI quartile had markedly higher odds than those in the lowest quartile: OR = 21.31, 95% CI 10.16–44.70
• All quartile-based associations and the overall trend remained statistically significant after Bonferroni correction for multiple comparisons
• Analysis was based on 3559 U.S. participants aged 20–59 years from NHANES 2011–2018 cycles

The association between MCMI and relative muscle loss was non-linear, with an inflection point at approximately MCMI 4.61.

• Below the threshold of MCMI 4.61, each 1-unit increase in MCMI was associated with substantially higher odds of relative muscle loss: OR = 3.52, 95% CI 2.78–4.45
• Above the threshold, the association appeared attenuated and statistically non-significant: OR = 1.10, 95% CI 0.67–1.82
• Non-linear trends were assessed using restricted cubic spline (RCS) models and threshold effect analyses

MCMI showed the highest discrimination for prevalent relative muscle loss compared to all other metabolic indices examined.

• MCMI AUC = 0.776
• Comparator AUCs: BMI = 0.727, CMI = 0.690, LAP = 0.708, TyG = 0.661, TyG-WC = 0.718
• Discrimination was assessed using receiver operating characteristic (ROC) curve analysis

A multivariable model incorporating MCMI with selected sociodemographic and clinical covariates achieved higher discrimination than MCMI alone.

• The multivariable model achieved an AUC of 0.828 in the training dataset
• This represented a modest improvement in statistical discrimination over MCMI alone (AUC 0.776)
• Key predictors were identified using LASSO regression with a 70/30 training-validation split
• Model performance was examined using ROC curves, calibration plots, and decision curve analysis (DCA)
• A nomogram was developed as an exploratory communication tool for visualizing cross-sectional probability estimates

The association between MCMI and relative muscle loss was generally consistent across subgroups but appeared stronger in men.

• P for interaction by sex = 0.002
• Subgroup analyses examined potential effect modification by age, sex, and other important covariates
• Associations were described as 'generally consistent across subgroups'

Relative muscle loss was defined using FNIH criteria based on appendicular lean mass adjusted by BMI.

• Relative muscle loss was defined as ALM/BMI < 0.512 for women and < 0.789 for men
• Definition was based on Foundation for the National Institutes of Health (FNIH) criteria
• ALM/BMI ratio was used as a proxy indicator for the low muscle mass dimension of sarcopenia-related phenotypes
• Study sample comprised 3559 U.S. participants aged 20–59 years from NHANES 2011–2018

The modified cardiometabolic index (MCMI) incorporates fasting plasma glucose in addition to the components of the conventional cardiometabolic index (CMI).

• Traditional CMI assesses central adiposity and lipid metabolism but does not directly reflect insulin resistance (IR)
• MCMI incorporates fasting plasma glucose and may better reflect IR-related metabolic dysfunction relevant to skeletal muscle health
• CMI is described as a conventional adiposity index