Association between a novel obesity indicator and chronic kidney disease as well as depression: A cross-sectional study based on NHANES 2009 to 2014

As a novel, simple, and accessible obesity index, Relative Fat Mass (RFM) provides a more precise estimate of body fat percentage. Current research on the associations of RFM with prevalent chronic kidney disease (CKD) and depression in individuals with CKD remains limited, particularly in representative United States populations. This study included participants from the National Health and Nutrition Examination Survey 2009 to 2014. RFM was calculated using the formula: 64 - (20 × height/waist circumference) + (12 × gender), where gender was coded as 1 (female) and 0 (male). Multivariable-adjusted logistic regression and restricted cubic spline analyses were performed to evaluate the associations of RFM with CKD and with depression in CKD patients. A mediation analysis was conducted to determine whether the association between RFM and CKD was mediated by hypertension and diabetes. Among 12,450 National Health and Nutrition Examination Survey participants, 1285 were diagnosed with CKD. In the fully adjusted logistic regression model, RFM was positively associated with CKD (adjusted odds ratio = 1.02, 95% confidence interval: 1.00-1.04, P = .015). Fully adjusted restricted cubic spline analysis showed a linear relationship between RFM and CKD (P for non-linear = 0.23), with an optimal cutoff value of 29.6. In addition, hypertension and diabetes mediated 30.34% (P < .001) and 21.08% (P = .002) of the association between RFM and CKD, respectively. Further fully adjusted logistic regression analysis revealed a positive association between RFM and depression in CKD patients (adjusted odds ratio = 1.05, 95% confidence interval: 1.01-1.08, P = .011). In the United States population, elevated RFM is associated with an increased risk of prevalent CKD, and it is also closely linked to a higher risk of depression in individuals with CKD.