Discussion of “Overweight and obese boys reduce food intake in response to a glucose drink but fail to increase intake in response to exercise of short duration”

Abstract

Tamam and collaborators recently proposed an interesting paper addressing the food intake and appetite response to an acute exercise and a glucose drink in normal weight and overweight–obese adolescents (Tamam et al. 2012). This paper adds great and useful results to the actual literature but to our mind some issues have to be underlined. The authors state that their paper is the first to provide data regarding the impact of acute effect of short exercise on energy intake in 9to 14-year-old boys while previous recent studies have explored the impact of three 10-min bouts of exercise (Thivel et al. 2011a, 2011b, 2012b). In this paper, overweight–obese adolescent boys do not modify their energy intake after a 15min bout of exercise set at their ventilatory threshold, whereas it has been shown that acute intensive exercise (>70% maximal oxygen consumption) was able to induce a decrease energy intake in such a population at the following ad libitum meal (Thivel et al. 2011a, 2011b, 2012b). The important exercise-induced energy expenditure differences between those last studies (about 300 kcal) and the present one (63 ± 7 kcal) may explain such a discrepancy, but we recently suggested that the energy expended during exercise does not explain the subsequent energy consumption since food intake was differentially affected after isoenergetic exercises at 2 levels of intensity (40% and 75% maximal oxygen consumption) (for review see Thivel et al. 2012a, 2012b). To our view the main reasons that Tamam et al. did not find any differences are the short duration of the follow-up, dinner energy intake was not examined, and most importantly, the use of ad libitum pizza buffets that are highly palatable and could have favoured inconsistent energy intake in those youths. In our previous work, we chose buffet meals composed of a high diversity of food without the participant’s preferred items to avoid the hedonic influence on food intake. The “non-homeostatic” regulation of energy intake certainly overpasses the physiological pathways involved in presence of highly palatable items (Finlayson and Dalton 2012). An important decreased food intake at dinner time without appetite modification (about 7 h after the exercise session) has also been reported by our group, whereas Tamam and colleagues suggested that the increased appetite sensation observed after exercise could favour higher energy consumption later in the day. Based on the already shown uncoupling effect of exercise on subjective appetite and effective energy consumption in both adults and youths (Flint et al. 2000; Mattes 1990; Thivel et al. 2011a, 2012b), it appears difficult to formulate such a hypothesis. Finally, the authors conclude that an acute short-term exercise set at the ventilator threshold was able to reduce energy balance because of energy expenditure and in the absence of subsequent energy intake compensation. However, the covered period in which to assess energy balance seems too short to hypothesize so (which was pointed out by the authors) as compensatory trends have been underlined in overweight– obese children who decrease their spontaneous energy expenditure after such an exercise for the rest of the day (Kriemler et al. 1999; Thivel et al. 2012a, 2012b). This compensatory response leads once more to the consideration of whether the best impact of physical activity for weight control and weight loss remains the induced energy expenditure or its impact on energy intake (Chaput and Sharma 2011). The paper proposed by Tamam and collaborators provides then interesting results concerning the impact of a glucose drink on food intake in lean and overweight–obese youths but the interpretation of their data on the energy in-