Author(s): RODRÍGUEZ GÓMEZ, I., MARTÍN-GARCÍA, M.1,2, ALEGRE, L.M.1,2, GARCÍA-CUARTERO, B.4, GONZÁLEZ-VERGAZ, A.4, CARCAVILLA, A.5, ARAGONÉS, A.6, ARA, I.1,2 , Institution: UNIVERSITY OF CASTILLA LA MANCHA, Country: SPAIN, Abstract-ID: 1347

INTRODUCTION:
With childhood obesity rates on the rise, researchers are studying the factors that explain excessive fat accumulation during growth, including exercise-related energy substrate metabolism [1,2]. Nevertheless, there are some factors involved that have not been entirely studied despite the fact that they are determinant, especially in pre-pubertal children [3]. Thus, the aim was to determine fat oxidation values during a graded cyclo-ergometer exercise in pre-pubertal children considering cardiovascular fitness (CRF) and lean mass based on obesity status and sex. Moreover, to elucidate whether body mass index (BMI) or fat accumulation mediate the relationship between CRF and fat oxidation.
METHODS:
We analysed 118 pre-pubertal children with Tanner ≤II (59 girls [11.5±2.0 yr]). Body composition was assessed using dual-energy X-ray absorptiometry and anthropometry, CRF (peak oxygen uptake -VO2peak) and fat oxidation rates were determined during a graded cycling test. Participants were classified as normal-weight, overweight or obesity according to the international cut-off points for BMI in children.
RESULTS:
In absolute values, obese pre-pubertal children displayed higher maximal fat oxidation (MFO) compared to overweight and normal-weight counterparts. However, after adjusting by CRF the difference in MFO disappeared. When MFO was expressed with respect to lean mass and adjusting by CRF, MFO in normal-weight children was significantly greater (7.2±0.3 vs. 6.9±0.5 vs. 6.4±0.4 mg·min-1·kgleanmass-1, normal-weight, overweight and obesity, respectively). Similar results were found in boys and girls. Furthermore, both fat accumulation and BMI acted as mediators in the relationship between CRF and fat oxidation (38%).
CONCLUSION:
Fat oxidation levels are comparable among pre-pubertal children, regardless of obesity status, upon CRF adjustment. Nevertheless, when contextualized within body and lean mass, obese and overweight children demonstrated reduced fat oxidation capacity compared to their normal-weight peers during exercise and with no sex-related differences. Thus, it seems that impaired metabolic flexibility due to obesity occurs even before the puberty independently of sex. Furthermore, fat mass seems to be a mediator factor between CRF and fat oxidation, which reinforces the need to consider obesity status when talking about energy substrate metabolism.