Exposure to CARDIovascular Risk Assessed by Cardiac Adiposity in oBese adOlescents Eligible to a Residential Long-term Lifestyle Intervention by Diet and eXercise (CARDIBOX)

The high prevalence of childhood obesity is a major public health issue, worldwide. Childhood obesity is associated with a high risk of cardiovascular events in adulthood, but recent studies also point out the development of cardiovascular complications in childhood or adolescence justifying the need for early detection and appropriate therapeutic management to prevent the development of more severe abnormalities. This project proposes to evaluate the myocardial function in a fine and comprehensive way (longitudinal, circumferential and radial linear deformations, and rotation / torsion mechanics) from the deformation imaging (MRI and high-resolution echocardiography), in obese adolescents following a lifestyle intervention combining diet and physical activity.

The investigators aim to improve knowledge of the association between epicardial adipose tissue, myocardial lipid content, and left ventricular regional myocardial function.

In this protocol, obese adolescents are recruited undergoing a 3-month lifestyle intervention residential program. Adolescents from the intervention group will be enrolled at the obesity center for the whole school year. The obesity center employs a multidisciplinary team to provide the best weight management care to adolescents during their stay. The weight loss program is an integral part of the obesity center program and fundamentally combines physical activity with a normocaloric diet monitored by a dietician. The physical activity program consists of two training sessions (aerobic and resistance training) per week. Moreover, adolescents will be engaged in two additional sessions per week, consisting in recreational activities such as ball and racquet games, trekking, snowshoeing or swimming.

There will be two measurement time: one at baseline (Day 0) and one at three months after the beginning of the lifestyle intervention (M3). The controls will be evaluated at baseline only.

Statistical analysis will be performed using Stata software (version 13; Stata-Corp, College Station, Tex., USA). All statistical tests will be two-sided and p inferior to 0.05 will be considered significant. Qualitative variables will be described in terms of numbers and proportions. Quantitative variables will be described in terms of numbers, mean standard deviation or median according to statistical distribution (normality studied using Shapiro-Wilk test). Graphic representations will be complete presentations of results. The main analysis will be performed with the Stata software (version 13, StataCorp, College Station). All statistical tests will be carried out at a risk of error of first species α set at 5%. Most of the analysis of the secondary evaluation criteria will be exploratory in nature and may lack power in terms of numbers. As discussed by Feise in 2002,104 the adjustment of the risk of error of 1st species will not be systematically proposed, but case by case in view of clinical considerations and not only statistical (e.g. Sidak correction for the analysis of correlation coefficients).

Qualitative variables will be described in terms of numbers and proportions. Quantitative variables will be described in terms of standard deviation or mean median according to statistical distribution (normality studied using Shapiro-Wilk test). Graphic representations will be complete presentations of results.

Intergroup comparisons will be systematically conducted without adjustment and by adjusting for factors whose distribution could be unbalanced between groups. Patients will be described and compared between groups at inclusion according to the following variables: compliance with eligibility criteria, epidemiological characteristics, clinical characteristics and characteristics of possible treatments. The baseline comparability of the two groups will be assessed on the main characteristics of the participants and potential factors associated with the primary outcome. A possible difference between the two groups on one of these characteristics will be determined according to clinical considerations and not solely statistical ones.

Eligibility Criteria:
Inclusion Criteria:

* age between 12 and 16 years old
* mature (menarche)
* suitable for physical activity
* able to give an informative consent
* affiliated at French insurance company
* consent from the legal representatives
* For obese adolescents: BMI greater than the 97th percentile of national curves.
* For the control group: to be normal-weighted (no obesity if overweight, \<85th percentile of national curves).

Exclusion Criteria:

* Medical or surgical history judged by the investigator as incompatible with the study
* Drugs that may interfere with the study results
* Cardiovascular, hepatic, psychiatric, renal, or endocrinological diseases
* Smoking
* Alcohol consumption
* Intense physical activity in competition