The Associations between Diet Quality, Total and Regional Adiposity, and Metabolic Risk in Hispanic and Non-Hispanic Adolescent Girls

Abstract

Nutrient deprived diets are major contributors to the development of childhood obesity and metabolic diseases. Total and site-specific adiposity, such as visceral and skeletal muscle fat, have been associated with an increased risk of metabolic syndrome, insulin resistance, and other cardiometabolic risk factors in youths. C-reactive protein (CRP), a circulating inflammatory biomarker, is an established risk factor for cardiovascular disease and is associated with adiposity even at a young age. Diet quality indexes have been developed for use in adolescents and have evaluated the relationships between diet quality and selected health outcomes. Studies that assess relationships between diet quality, adiposity measured using direct methods, and metabolic risk are lacking in youth, particularly Hispanic Americans. Therefore, the objective of this dissertation was to evaluate the relationships between diet quality, assessed by the Youth Healthy Eating Index (YHEI), measures of total and site-specific adiposity, by dual-energy x-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT), and inflammation, assessed by high-sensitivity CRP (hs-CRP) in a cross-sectional study at baseline of 576 healthy Hispanic American and non-Hispanic girls aged 8-13 years. Diet was assessed using the validated semi-quantitative Harvard Youth/Adolescent Food Frequency Questionnaire (YAQ). Diet quality was assessed from the YHEI, developed based on the YAQ. Muscle density (mg/cm³), a surrogate for fat infiltration, was measured at tibial and femoral sites using pQCT. Total body and android fat (surrogate for visceral fat) were measured by DXA. Serum hs-CRP concentrations were measured by nephelometry. Multiple linear and logistic regression analyses were employed to assess these relationships. Total YHEI score was inversely associated with total body fat percent (p= 0.01) and android percent fat (p= 0.02), but not body mass index (BMI) or muscle density. Lower "margarine and butter use" and higher "meat ratio" were associated with higher leg muscle density. Higher "meat ratio" was inversely associated with BMI and greater "multivitamin use" was inversely associated with visceral adiposity. In a subsample of 113 Hispanic girls, over 50% of study participants demonstrated non-detectable serum hs-CRP levels. In adjusted models, there was no significant relationship between overall YHEI score and hs-CRP in this sample of adolescent girls. For every 1-unit increase in "whole grains" score there was a 44% increase in odds of being in the "high" category compared to the "undetectable" category of hs-CRP, after adjusting for maturity offset, PYPAQ score, total energy intake, total body fat, and all other individual YHEI components (OR: 1.44, 95% CI: 1.06, 1.97). The odds of being in the "high" category of hs-CRP were 38% higher compared to those with "non-detectable" hs-CRP for every 1-kg/m² increase in BMI (OR: 1.33, 95% CI 1.16, 1.53, p<0.0001). The odds of being in the "high" hs-CRP category increased with every 5 percent unit increase in total body percent fat (OR: 2.38, 95% CI 1.58, 3.58, p<0.0001) and android percent fat (OR: 1.89, 95% CI 1.39, 2.57, p<0.0001), compared to those with "non-detectable" concentrations. Calf muscle density was associated with lower odds of elevated hs-CRP compared to the "non-detectable" group (OR: 0.58, 95% CI 0.35, 0.75, p<0.001). The findings suggest that higher diet quality scores are associated with lower total and visceral body fat in adolescent girls. While greater total and regional adiposity are associated with increased inflammation, independent of biological and lifestyle factors, diet quality is not significantly associated with inflammation, as assessed by concentrations of hs-CRP, in Hispanic American girls.