Association between cardiorespiratory fitness level and insulin resistance in adolescents with various obesity categories

Abstract

BACKGROUND

An association between cardiorespiratory fitness (CRF) and insulin resistance in obese adolescents, especially in those with various obesity categories, has not been systematically studied. There is a lack of knowledge about the effects of CRF on insulin resistance in severely obese adolescents, despite their continuous rise.

AIM

To investigate the association between CRF and insulin resistance in obese adolescents, with special emphasis on severely obese adolescents.

METHODS

We performed a prospective, cross-sectional study that included 200 pubertal adolescents, 10 years to 18 years of age, who were referred to a tertiary care center due to obesity. According to body mass index (BMI), adolescents were classified as mildly obese (BMI 100% to 120% of the 95^th percentile for age and sex) or severely obese (BMI ≥ 120% of the 95^th percentile for age and sex or ≥ 35 kg/m², whichever was lower). Participant body composition was assessed by bioelectrical impedance analysis. A homeostatic model assessment of insulin resistance (HOMA-IR) was calculated. Maximal oxygen uptake (VO₂max) was determined from submaximal treadmill exercise test. CRF was expressed as VO₂max scaled by total body weight (TBW) (mL/min/kg TBW) or by fat free mass (FFM) (mL/min/kg FFM), and then categorized as poor, intermediate, or good, according to VO₂max terciles. Data were analyzed by statistical software package SPSS (IBM SPSS Statistics for Windows, Version 24.0). P < 0.05 was considered statistically significant.

RESULTS

A weak negative correlation between CRF and HOMA-IR was found [Spearman’s rank correlation coefficient (r_s) = -0.28, P < 0.01 for CRF_TBW; (r_s) = -0.21, P < 0.01 for CRF_FFM]. One-way analysis of variance (ANOVA) revealed a significant main effect of CRF on HOMA-IR [F₍₂₂₀₀₎ = 6.840, P = 0.001 for CRF_TBW; F₍₂₂₀₀₎ = 3.883, P = 0.022 for CRF_FFM]. Subsequent analyses showed that obese adolescents with poor CRF had higher HOMA-IR than obese adolescents with good CRF (P = 0.001 for CRF_TBW; P = 0.018 for CRF_FFM). Two-way ANOVA with Bonferroni correction confirmed significant effect of interaction of CRF level and obesity category on HOMA-IR [F₍₂₂₀₀₎ = 3.292, P = 0.039 for CRF_TBW]. Severely obese adolescents had higher HOMA-IR than those who were mildly obese, with either good or poor CRF. However, HOMA-IR did not differ between severely obese adolescents with good and mildly obese adolescents with poor CRF.

CONCLUSION

CRF is an important determinant of insulin resistance in obese adolescents, regardless of obesity category. Therefore, CRF assessment should be a part of diagnostic procedure, and its improvement should be a therapeutic goal.

Keywords: Cardiorespiratory fitness; Insulin resistance; Obese adolescents; Severe obesity; Obesity category

Core Tip: The association between obesity and insulin resistance is well established. However, data concerning the relationship between cardiorespiratory fitness (CRF) and insulin resistance in obese adolescents, especially in those with varying obesity categories, are quite limited. The results of present study show that obese adolescents with good CRF have lower homeostatic model assessment of insulin resistance (HOMA-IR) than obese adolescents with poor CRF. Moreover, there is no difference in HOMA-IR between severely obese adolescents with good CRF and mildly obese adolescents with poor CRF. Thus, the improvement of CRF in obese adolescents, including those with severe obesity, should be a therapeutic goal.