Impact of Meal Caloric Content on the Thermic Effect of Food in Adolescents With Obesity.

The thermic effect of food (TEF) represents an important but often overlooked component of total energy expenditure. The effects of meals with varying energy content but identical macronutrient distribution on TEF are unclear in adolescents with obesity. This study examined the effects of increasing meal energy on TEF, appetite, and food reward. Fifteen adolescents with obesity completed a randomized crossover trial with three lunch test meals (700, 1000, 1300 kcal) matched for macronutrient distribution. Postprandial energy expenditure was measured over 5 h to assess TEF, while appetite and food reward were assessed using visual analog scales and the Leeds Food Preference Questionnaire, respectively. TEF differed by meal size (p < 0.001), with the 1300-kcal meal eliciting a greater TEF than the 700-kcal meal (β = 0.12 kcal·min-1, 95% CI [0.06, 0.18], p < 0.001). Differences between the 700- and 1000-kcal meals were not significant, and the 1000- versus 1300-kcal comparison showed a trend toward significance. Relative TEF (% of meal energy) did not differ between meals. Appetite ratings were unaffected by meal size. Food reward measures were largely unaffected by meal condition, with isolated differences in sweet appeal bias and explicit liking for high-fat sweet foods. In adolescents with obesity, TEF increases only with large differences in meal energy and remains proportional to energy intake. Together, the stable TEF and the absence of differences in appetite or food reward suggest that larger meals may not promote greater satiety, potentially favouring higher daily energy intake relative to energy expenditure.