The prevention and management of pediatric obesity require a thorough understanding and consideration of the different components of energy balance (i.e., intake and expenditure) and their interactions. Total energy expenditure (TEE) consists of resting metabolism (RM), energy expenditure induced by physical activity (EEPA), and dietary thermogenesis (DTE). While RM and EEPA are the two main contributors to TEE, DTE is often overlooked, even though it can account for around 10% of our daily energy expenditure. In fact, few studies have prioritized the evaluation of the thermic effect of food (TEF), defined as the increase in energy expenditure above the basal metabolic rate when fasting, despite the fact that it accounts for about 10% of total daily energy expenditure . It has been suggested that TEF may play a role in the development or maintenance of obesity.

Some studies indicate a reduction in TEF in individuals living with obesity , possibly due to lower postprandial activation of the sympathetic nervous system, thereby limiting the thermogenic response after meals . Conversely, several studies have reported no decrease in TEF in individuals living with obesity . Due to these contradictory results, no consensus has been reached on the FET response in individuals with obesity compared to those of normal weight.

The limited number of available results can be explained not only by a lack of interest in this TEF among scientists and clinicians, but also by the methodological difficulties involved in its assessment. Indeed, the latter requires indirect calorimetry measurements over a period of up to 5 to 6 hours after a meal, as well as careful calibration of the test meals used, their qualitative content, and their caloric content. These factors are all the more important to consider given that a systematic review has shown that TEF is influenced by the energy intake of the meal as well as its macronutrient composition, with proteins and carbohydrates inducing a higher TEF than lipids . However, several uncertainties remain, particularly regarding the choice of test meal, which could be standardized for all participants or adjusted according to their body composition.

While our team recently conducted a systematic review of the literature in this area, identifying a glaring lack of evidence, the few results available suggest a potential reduction in TEF in obese children and adolescents, contributing to a minimization of the optimization of their daily energy balance. In their study, Maffeis and colleagues show, for example, a significantly reduced TEF in adolescents with obesity compared to their normal-weight counterparts, despite a higher-calorie test meal adapted to their energy needs . These results are consistent with those proposed by Salas-Salvado the following year, who suggested a reduced TEF in obese adolescents, associated with their percentage of body fat . This research suggests the need to consider the effects of weight status, body composition, and the caloric composition of a meal in order to better understand TEF in this population.

Unfortunately, this area has not been explored in depth since the 1990s, even though the prevalence of pediatric obesity continues to rise.

In this context, the objective of this study is to explore dietary thermogenesis in response to meals of different caloric content in obese adolescents.

Inclusion Criteria:

• • Adolescents aged 11 to 17 (inclusive), at Tanner stage 3-5 of sexual maturation,

  • With obesity defined as a body mass index (BMI) above the 97th percentile according to national growth charts,
  • Adolescents affiliated with the social security system or equivalent,
  • Adolescents who have been informed and have given their written consent to participate in the study.

Exclusion Criteria:

• Refusal to participate in the study,
• Refusal of consent by legal guardians,
• Regular consumption of tobacco or alcohol,
• Special diet,
• Participation in regular and intense physical and sporting activities,
• Medical or surgical history deemed by the investigator to be incompatible with the study,
• Presence of diabetes, and any other condition limiting the application of either strategy being tested,
• Adolescents undergoing energy restriction or a weight loss program through physical activity at the time of inclusion or during the last 6 months,
• Taking medication that may interfere with the study results.
• Adolescents with cardiovascular problems, i.e., subjects with a history of cardiovascular and/or neurovascular disease, as well as subjects with cardiovascular and/or neurovascular risk factors (excluding obesity/overweight).
• Surgery in the previous 3 months,
• Adolescents who are currently excluded from another study,
• Pregnant or breastfeeding adolescents,
• Adolescents under guardianship/curatorship or legal protection,
• Parents under guardianship/curatorship or legal protection.