Discussion of “Influence of netball-based exercise on energy intake, subjective appetite and plasma acylated ghrelin in adolescent girls”

Abstract

Rumbold and colleagues recently published an innovative and interesting paper addressing the energy intake, subjective appetite, and acylated ghrelin response to a netball-based exercise session in lean adolescent girls (Rumbold et al. 2013). This paper deals with one of their previous publications (Rumbold et al. 2011) and adds some interesting results to the current literature in the field. However, some issues warrant discussion. Rumbold et al. (2013) showed that energy intake of the adolescents at the test meal following the exercise session (lunch time) was not affected compared with the control, sedentary session (Rumbold et al. 2013). First, it needs to be noticed that the authors offered a test meal that was composed only of white pasta in a tomato andherb saucewith gratedmild cheddar cheese. Although this is in line with their previous work, the adolescents were not offered to choose among several items (e.g., buffet-style meal), which limits the ability of the authors to quantitatively analyze energy intake in this sample (Thivel et al. 2012a). Moreover, the authors indicated that the adolescents participated in sedentary activities during the control session and were free to engage in sedentary activities such as reading, watching TV, or completing school work for an hour between the netball-based exercise session and the test meal. Regarding the current literature on the impact of daily activities on subsequent energy intake, it can be argued that the assessed energy intake at lunch time was more affected by those sedentary activities than by the netball session itself. Previous studies have effectively emphasized the stimulating influence of screen-based sedentary activities such as watching television or playing video games on subsequent food intake in children and adolescents (Thivel et al. 2012c). For instance, Nemet and collaborators have observed a higher food consumption after 45 min of TV viewing compared with 45 min of physical activity (swimming or resistance training) in prepubertal kids (Nemet et al. 2010). Similarly, a 1-h passive video game session has been shown to favor increased energy intake in lean adolescent boys without altering appetite sensations comparedwith 1 h of rest (Chaput et al. 2011). Along the same lines, cognitiveworking such as reading andwritinghas been shown to increase foodconsumption in students (Chaput et al. 2008;Chaput and Tremblay 2007). Finally, recent data point out that imposed sedentary behaviors (e.g., prolonged sitting or bed rest) have the opposite effect on energy intake compared with exercise in adolescents (Thivel et al. 2012b); bed rest has been shown to have an orexigenic effect,whereas acute exercise favors reduced energy consumption in adolescents (Thivel et al. 2012b). Collectively, the paper by Rumbold et al. provides interesting new results to the field but also highlights the need for rigorous methodologies (controlling for the influence of screen-based sedentary behaviors on food intake) to ensure valid conclusions. The use of sedentary or imposed sedentary activities as control sessions is an important issue and (or) problem to consider in future studies if we want to avoid the confounding effect of these activities on eating behavior.