Differential Relationship Between Thigh and Calf Intramuscular Adipose Tissue Depots and Indices of Metabolic Health in Older Overweight and Obese Adults

Abstract

IntroductionAccumulation of intramuscular adipose tissue (IMAT) is associated with insulin resistance, but there are limited data comparing the predictive ability of different IMAT stores with markers of metabolic health.PurposeThe purpose of this secondary analysis study was to investigate associations among thigh and calf IMAT stores and indices of metabolic health in older overweight and obese adults.MethodsSeventy‐three subjects (25 men, 48 women, age: 58 ± 11 y, BMI: 29.9 ± 4.9 kg/m2, mean ± SD) completed dietary interventions with (n=48) or without (n=25) energy restriction‐induced weight loss and thigh and calf compositions were assessed via magnetic resonance imaging. IMAT, IMAT volume to total tissue volume (TT) ratio, and IMAT to muscle tissue volume (MT) ratio were regressed separately against fasting serum glucose, insulin, homeostatic model assessment‐insulin resistance (HOMA‐IR), and lipid‐lipoprotein profile parameters. A multiple linear regression modeling procedure was performed on baseline (adjusted for age and sex) and change values (adjusted for age, sex, baseline dependent variable) and adjusted regression coefficients (β*) are reported. Significance level was set at p<0.05 and all β* values herein meet significance.ResultsThigh IMAT is predictive of metabolic health parameters, while calf IMAT is not. Conversely, changes in calf IMAT from dietary intervention predict improvement of metabolic health indices, whereas thigh IMAT does not. Baseline thigh IMAT was associated with fasting serum insulin, HOMA‐IR, and serum triacylglycerol (TG). Baseline thigh IMAT:TT was associated with fasting serum glucose, insulin, HOMA‐IR, TG, total cholesterol (TC), and inversely associated with TC:HDL, while baseline thigh IMAT:MT was associated with TC and TG. There were no associations between baseline calf IMAT variables and metabolic health indices. No associations were detected between changes (Δ) in thigh IMAT and Δs in metabolic health indices. However, calf ΔIMAT was associated with Δ insulin, ΔHOMA‐IR, ΔTG, ΔTC and inversely associated with ΔTC:ΔHDL. Calf ΔIMAT:ΔMT was associated with Δ insulin, ΔHOMA‐IR, and ΔTC.ConclusionsThese data support the consensus that IMAT is associated with insulin resistance, and implicate IMAT to impact lipid‐lipoprotein profile. Further, improvement in metabolic health indices may be better predicted by changes in calf IMAT than by changes in thigh IMAT in older overweight and obese adults participating in weight loss and weight stability dietary interventions.Support or Funding InformationPurdue Center for Aging and Life Course; American Egg Board‐Egg Nutrition Center; National Dairy Council; NIH UL1TR001108; Purdue Ingestive Behavior Research Center