Objective: To determine if obesity measures are related to measures of low-density lipoprotein (LDL) size and LDL subfractions in a population of Mexican-Americans with high prevalence of obesity.
Methods: LDL size phenotypes, based on nondenaturing gradient gel electrophoresis and staining for cholesterol (using Sudan black B), were determined for 313 unrelated Mexican-American participants in the San Antonio Family Heart Study. LDL size measures included predominant particle diameter, median diameter (particle diameter, where half the LDL absorbance is on larger and half on smaller LDLs) and cholesterol level in various LDL subfractions. Adiposity traits included two measures of general body fatness (body-mass index (BMI) and fat mass determined with bioimpedance) and three measures of regional fat deposition (waist-to-hip ratio (WHR), waist circumference and subscapular-triceps skinfold ratio (STR)).
Results: Gender and diabetes were significantly associated with most LDL size measures. In addition, BMI, WHR, waist circumference and STR were significantly (P<0.05) associated with several LDL size measures. Stepwise regression analysis (including adjustment for age, gender and diabetes status) showed that in every case, the strongest adiposity correlate of LDL size, was WHR, which reflects deposition of visceral fat. If triglyceride (TG) concentration was also included in the models, no fat measure was independently correlated with LDL size, suggesting that elevation of TG, associated with increased adiposity, was more directly correlated with LDL size. Supporting this interpretation, we found that WHR was also the strongest correlate of TG among adiposity measures. Regression analysis of the LDL particle size cholesterol profile expressed in 0.1 nm increments revealed a positive correlation of WHR and LDLs in the interval 25.9-26.3 nm (P < 0.05) and a negative correlation of BMI with LDLs in the interval 27.3-28.1 nm (P < 0.05).
Conclusion: These results suggest that different adiposity measures, reflecting different aspects of fat deposition, are related to specific LDL size intervals. We speculate that increased deposition of fat, particularly visceral fat, is associated with increased TG, which in turn is associated with decreases in LDL particle size.