Introduction: Insulin resistance is increasingly found in the paediatric age
group, resulting from elevated endogenous glucose production (hepatic
glycogenolysis and gluconeogenesis) and/or altered glucose utilization (glucose
oxidation and glycogen synthesis). These variables can be computed from the
simultaneous use of indirect calorimetry and breath 13CO2 measurement, both
non invasive methods. Objective: Predicting insulin resistance in targeted
subjects requires to establish first the normal developmental pattern of glucose
oxidation and glycogen turnover in school-aged children. Patients/Material and
Methods: A beverage containing naturally enriched 13C maize glucose was
given every hour during four hours, at a rate of 3 mg/kg/min, to 47 lean healthy
subjects of both sexes, aged 12.4 ± 2.6 yrs (mean ± SD) of whom 11 aged 7-9
yrs (group 1, G1), 20 aged 10-13 yrs (G2) and 16 aged 14-17 yrs (G3). Energy
expenditure (EE) and total glucose oxidation (TGO) were measured during the
last two hours by indirect calorimetry. Exogenous glucose oxidation (EGO) was
determined by the analysis of 13CO2 production in expired air. Glycogen
degradation (GD) (mostly hepatic in resting conditions) was calculated as [TGO
- EGO], and total glycogen synthesis (TGS) (liver and skeletal muscle) was
calculated as [glucose intake - EGO]. Results: EE correlated negatively with age
(r = -0.76, p < 0.001) as well as TGO (r = -0.66, p < 0.001) and GD (r = -0.59,
p < 0.001), whereas EGO and TGS did not change signficantly. When expressed
as age groups, EE decreased from 0.025 (G1) to 0.017 kcal/kg/min (G3) (p <
0.001). TGO fell from 4.61 (G1) to 4.25 (G2) and 2.93 mg/kg/min (G3) (p <
0.001 vs G1 and G2). Values for GD was 2.58, 2.30 and 1.23 mg/kg/min
respectively (p = 0.004 for G3 vs G1 and p = 0.003 for G3 vs G2). Conclusions:
1) Indirect calorimetry coupled with breath 13CO2 measurement after oral
glucose intake can easily be used in school-aged children. 2) This original non
invasive procedure allows to assess glycogen degradation and synthesis
simultaneously and, consequently, to describe the developmental pattern of
whole body glycogen turnover in health and disease. 3) This pilot study shows
significant changes in EE, TGO and GD with age in healthy subjects. These new
data provide standardized values to be used in the evaluation of subjects at risk
to develop anomalies of glucose metabolism.