Maximal fat oxidation during aerobic exercise in adolescents with type 1 diabetes

Objective: To compare maximal fat oxidation rates (FATMAX) and analyze their association with cardiorespiratory fitness in adolescents with type 1 diabetes mellitus (T1DM). Methods: Twenty-two male and female adolescents aged between 11 to 17 years, following clinical and anthropometric evaluations, were assigned to the diabetic group (DG; n = 10) or control group (CG; n = 12). Cardiorespiratory fitness was determined by maximal oxygen uptake (VO2max) during a maximal aerobic test on a cycle ergometer using the Balke protocol. Maximal fat oxidation (FATMAX) was determined by the respiratory exchange ratio proposed in the Lusk table. Results: Adolescents in the DG had lower mean FATMAX (p<0.01) and %VO2FATMAX(p=0.001) values when compared with those in the CG. FATMAX values were inversely correlated with serum glycosylated hemoglobin (HbA1c) levels (r= -0.77) and directly correlated with BMI z-scores (r=0.76), while %VO2FATMAX results were correlated with age (r=0.81), BMI z-scores (r=0.65), and VO2max values (r=0.81). On multiple linear regression, HbA1c values explained 54% (adjusted r(2) =0.54, p=0.009) and BMI z-scores explained 3.1% (adjusted r(2) =-0.031, p=0.009) of the variation in FATMAX in the DG. Adolescents with T1DM had similar cardiorespiratory fitness and lower FATMAX rates (35 +/- 11 VO2max) when compared with controls (60 +/- 12 VO2max). Conclusion:These results suggest lower fat oxidation rates and greater use of glucose as an energy substrate during exercise and worse control in T1DM. Therefore, results may contribute to appropriate exercise prescription in T1DM, after verifying exercise intensity to reduce hypoglycemia risk.