Resting Whole Body Energy Metabolism in Class 3 Obesity; from Preserved Insulin Sensitivity to Overt Type 2 Diabetes.

CONTEXT

Insulin resistance and diabetes may influence separately or in combination whole body energy metabolism.

OBJECTIVE

To assess the impact of insulin resistance and/or overt type 2 diabetes on resting energy expenditure (REE) in class 3 obese individuals.

DESIGN AND SETTING

Retrospective, cross-sectional analysis of a set of data about individuals attending the outpatients service of a single center of bariatric surgery between January 2015 and December 2017.

PATIENTS

We screened 382 patients in which abnormal thyroid function was excluded, and segregated them in three groups of subjects: patients with type 2 diabetes (T2DM; n=70), non-diabetic insulin-resistant patients with HOMA-IR ≥ 3 (n=236), non-diabetic insulin-sensitive patients with HOMA-IR < 3 (n=75).

MAIN OUTCOME MEASURE

Resting energy expenditure (REE), body composition and insulin resistance assessed using indirect calorimetry, bioimpedance and HOMA-IR.

RESULTS

Non-diabetic insulin-sensitive patients resulted to be younger, with lower BMI and higher prevalence of female subjects; meanwhile, non-diabetic but insulin-resistant patients and T2DM patients were not different in terms of anthropometric parameters. REE was higher in T2DM than in non-diabetic insulin-resistant and insulin-sensitive individuals when expressed as percent of the predicted REE (based on Harris Benedict equation) (p<0.0001) or when adjusted for kg of free fat mass (p<0.0001) and was found to be higher also in insulin-resistant vs insulin-sensitive patients (p<0.001). The respiratory quotient was different between groups (0.87±0.11, 0.86±0.12 and 0.91±0.14 in T2DM, insulin-resistant and insulin-sensitive patients, respectively; p<0.03). Regression analysis confirmed that HOMA-IR was independently associated with the REE (R=0.110, p<0.001).

CONCLUSION

Class 3 obese patients with normal insulin sensitivity are characterized by reduced fasting REE in comparison to insulin-resistant obese patients and obese patients with short duration of diabetes supporting the hypothesis that down-regulation of nutrients' oxidative disposal may represent an adaptation of energy metabolism in obese individuals with preserved insulin sensitivity.