The present study examined the mediating influences of snacking while watching television and the perceived value of television viewing on the longitudinal association between television viewing and eating behaviours in a large regionally diverse sample of Australian adolescents. Adolescents who watched more than two hours of television per day had higher intakes of energy-dense snacks and drinks, and lower intakes of fruit two years later. Furthermore, the associations were mediated by snacking while watching television and perceived value of television viewing. The importance of explicating the mechanisms through which television viewing influences adolescent eating behaviours not only relates to the advancement of scientific knowledge: Understanding these mechanisms is also crucial because it offers potential avenues for targeted intervention programmes.
Cross-sectional studies have found associations between television viewing and unhealthy eating behaviours in pre-school children [48, 49], school-aged children [50, 51], adolescents [52, 53], and adults [54, 55]. Longitudinal studies examining the associations between television viewing and eating behaviours are becoming more prevalent; however, data on adolescents comes predominantly from the US. Data from project EAT has shown television viewing to be predictive of lower fruit and calcium intakes, and higher sugar-sweetened beverage and fast food intakes after five years [22–24]. Other prospective research from the US has shown that for each hour increase in television viewing adolescents consumed additional energy intake of 106 kcal a day  and decreased intakes of fruit and vegetables . Findings from the current study support and add to previous studies by showing that adolescents in Australia who watch more television are more likely to have poorer eating behaviours. The present study also supports previous literature showing that television viewing is associated with snacking while watching television [28, 29], and that snacking while watching television is positively associated with consumption of energy-dense snacks and drinks, and negatively associated with consumption of fruit [13, 26]. For some young people a significant proportion of their daily energy intake is consumed while watching television . Experimental studies have shown that watching television while eating may cause a distraction resulting in a delay in normal mealtime satiation and a reduction in internal satiety signals [58, 59], which may lead to overeating. Given that adolescence is a critical developmental period, during which lifelong behaviours are formed , the present findings suggest that examining methods to modify television viewing and snacking and eating behaviours in front of the television should be a priority for nutrition promotion.
The present study advances previous findings by demonstrating that variations in snacking while watching television play an important role in mediating the associations between television viewing and adolescents' intakes of energy-dense snacks and drinks, and fruit 2-years later. This is a novel finding, since to the best of our knowledge, no previous studies have examined potential mediating influences of the association between television viewing and eating behaviours in adolescents. Snacking while watching television partially explained (mediated) the positive association between television viewing and consumption of energy-dense snacks and drinks, and the negative association between television viewing and consumption of fruit. While watching television, adolescents are exposed to a larger number of advertisements, which are more often for energy-dense foods compared to fresh foods such as fruits and vegetables . Previous research has shown that television advertising directed at young people influences their preferences, requests and short-term consumption of foods and beverage products advertised on television . It may be, therefore, that those adolescents who watch more television, subsequently prefer, request and consume as snacks more of the types of foods advertised, which would explain the associations observed between these variables. Such findings suggest that reducing television viewing and changing snacking habits while watching television may be important strategies for improving the overall healthfulness of adolescent eating behaviours.
The present study found that the perceived value of television viewing varied by the amount of time spent watching television. Adolescents who watched more television placed a higher value on television viewing than those who watched less. This part of the model was cross-sectional so we cannot rule out reverse causality. For many young people, sedentary behaviours such as television viewing have a high reinforcing value (motivation to participate), so they are more likely to become sedentary and less likely to develop a regular physical activity habit . Furthermore, accessibility of sedentary behaviours is much easier than that for physical activity for most people , which increases the amount of motivation people need to choose activity over more sedentary pursuits. Experimental research using positive reinforcement to reduce sedentary behaviours and increase the accessibility of physical activity has had mixed success at increasing physical activity [43, 63, 64]. Future research should examine the applicability of such an approach in real world settings.
Further analyses showed that the value that adolescents placed on television viewing partially explained (mediated) the association between television viewing and consumption of energy-dense snacks, drinks and fruit. Again, this is a novel finding, since to the best of our knowledge, no previous studies have examined potential mediating influences of the association between television viewing and eating behaviours in adolescents. A potential explanation for such associations is that if adolescents place a high value on watching the television, they are more likely to take on board the messages promoted, which as mentioned above, are likely to encourage the consumption of energy-dense foods and drinks rather than more healthy snacks (e.g. fruit). Future research aiming to improve adolescent eating behaviours should assess the efficacy of methods to address the values that adolescents place on television viewing.
In considering these findings it is important to acknowledge the limitations of the study. There was some loss of participants at follow-up and some differences between those with follow-up data and those with baseline only data, although the sample at follow-up remained diverse. All data were collected by self-report and are subject to socially desirable response bias or other misreporting. T2 data is not available for the examined mediating variables, and thus we were not able to examine changes in these variables over time. When using observational data, prospective relationships can, as for cross-sectional data, be due to a third antecedent. Thus, we do not assume causality. Strengths of the study include its longitudinal design, the large regionally diverse sample, and the use of powerful statistical mediation techniques.