The non-advertising effects of screen-based sedentary activities on acute eating behaviours in children, adolescents, and young adults. A systematic review

Highlights

• Screen-based (SB) activities increase dietary intake in the absence of TV food advertising.

• Potential mechanisms include distraction, conditioning, and interruption of food regulation.

• Studies to date have focused primarily on the effects of TV rather than computer and video games.

• Limited research into comparative effects of different SB activities on acute dietary intake.

Abstract

Sedentary screen time may be an important determinant of childhood obesity. A number of potential mechanisms to explain the link between screen time and increased bodyweight have been proposed; however, the relationship appears to be best explained by the effects on dietary intake, which is attributed to either food advertising or effects independent of food advertising. Technological advances have allowed for greater accessibility and exposure to advertisement-free screen-based media. This review was conducted to systematically synthesise the evidence from laboratory based studies which have investigated the non-advertising effects of screen time (TV viewing, sedentary video games, and computer use) on dietary intake in children, adolescents, and young adults. MEDLINE, PubMed, PsychInfo, CINAHL, and Embase were searched from inception through 5 July 2013. Ten trials met the inclusion criteria and were included in the review. Risk of study bias was judged to range from low to high. Screen time in the absence of food advertising was consistently found to be associated with increased dietary intake compared with non-screen behaviours. Suggested explanations for this relationship included: distraction, interruption of physiologic food regulation, screen time as a conditioned cue to eat, disruption of memory formation, and the effects of the stress-induced reward system. Due to the limited number of high-quality studies available for this review, our findings are preliminary. More work is required to better establish the link between dietary intake and advertisement-free screen time and assess whether differences exist between the different screen-based activities.

Introduction

The aetiology of obesity is complex (Michael, Rudolph, & Jules, 1997). Yet despite this complexity, environmental changes, rather than genetic, have been identified as the most important determinant for the increase in adiposity in recent years (Rey-Lopez, Vicente-Rodriguez, Biosca, & Moreno, 2008), with screen-based sedentary behaviour acknowledged as one such critical environmental change (Kautiainen, Koivusilta, Lintonen, Virtanen, & Rimpelä, 2005). While sedentary behaviours include any waking activities requiring very little energy expenditure (⩽1.5 metabolic equivalents) and which involve sitting or lying down (Sedentary Behaviour Research Network., 2012), screen-based sedentary behaviours refer to a sub-set of these activities and include watching television (TV), playing video games, or using a computer. Accessibility to these screen-based sedentary activities has increased at an alarming rate in recent decades and has been linked with a dramatic increase in sedentary time (Nelson, Neumark-Stzainer, Hannan, Sirard, & Story, 2006). This issue of sedentariness due to increased screen time is a growing public health concern. Evidence from longitudinal studies has linked screen-based sedentary behaviours with increased body mass index (BMI) in children, even after adjusting for physical activity levels (Elgar et al., 2005, Proctor et al., 2003, Robinson, 1999). The implications of this are compounded by the finding that screen time appears to be a relatively stable behaviour, tracking from childhood to both adolescence (Valerio et al., 2006) and adulthood (Biddle, Pearson, Ross, & Braithwaite, 2010).

A large number of interventions have been conducted in recent years in an attempt to curb the effects of screen-based sedentary behaviours on obesity. Despite such interventions tending to produce statistically significant improvements in measures of both sedentary time and BMI, improvements have often been small and of little clinical significance (DeMattia et al., 2007, Leung et al., 2012). This inability of interventions to effect large changes in outcomes may be the consequence of our limited understanding of the specific mechanisms by which screen-based sedentary behaviours and obesity are linked. A better appreciation of these mechanisms may allow targeting of specific health-related behaviours responsible for the relationship between screen time and obesity. It is therefore proposed that in order to design and implement more effective screen-based sedentary behaviour interventions, we first need to better describe the mechanisms by which these activities are linked with obesity.

Two main mechanisms have been proposed for the link between screen-based activities and obesity: (1) the effects of screen time on decreased physical activity levels (Jenvey, 2007, Robinson, 2001), and (2) the effects of screen time on increased energy intake (Boulos et al., 2012, Hastings et al., 2003, Robinson, 2001). Evidence for the displacement of physical activity is conflicting, (Marshall, Biddle, Gorely, Cameron, & Murdey, 2004), and data suggest that even independent of physical activity, TV watching remains an important risk factor for adiposity (Ekelund et al., 2006, Gebremariam et al., 2013). Indeed, the connection between screen time and increased energy intake appears better substantiated by research.

Food advertising has been shown to influence both food consumption and food preferences, especially in children (Boyland, Harrold, Kirkham, Corker, et al., 2011, Harris et al., 2009, Robinson, 2001). An important finding is that food advertising is not only positively associated with food intake (Bellisle et al., 2004, Blass et al., 2006, Jackson et al., 2009), but that it is also associated with decreased consumption of fruit and vegetable intake (Boynton-Jarrett et al., 2003, Coon et al., 2001). Within a laboratory setting, children have also been shown to consume greater amounts of sweet foods (high and low in fat) and high-fat savoury foods following exposure to food advertisements on TV compared with children who only viewed non-food advertisements (Halford, Gillespie, Brown, Pontin, & Dovey, 2004). These findings are particularly disturbing given that food companies often target children, as evidenced by the pervasiveness of food advertisements during children’s programming (Boyland, Harrold, Kirkham, Halford, et al., 2011, Effertz and Wilcke, 2012, Haug et al., 2009, Kelly et al., 2011).

However, there is also a growing body of evidence to suggest that screen-based activities, even in the absence of TV food advertising, increase dietary intake (Chaput, Visby, et al., 2011, Volkow et al., 2012). This is of significance for two main reasons: (1) accessibility to video content without TV food advertisements has increased, and (2) youth are now exposed to a number of competing screen-based activities that may draw attention away from TV advertisements. Firstly, with respect to accessibility, technological advances have enabled consumption of greater amounts of advertisement-free video content via video-on-demand technologies (Carlson, 2006). Such technologies allow advertisement-free video content to be streamed or downloaded to media devices, such as computers or portable media players. This has resulted in young people now having some control over how much TV advertising they are exposed to. Secondly, with respect to competing screen-based behaviours, there is evidence to suggest that TV viewing is now combined with other screen-based activities, which may distract the viewer’s attention away from advertising. In 2003 it was reported that 46% of time spent watching TV was actually spent engaged in a secondary behaviour, such as social interactions and playing, with non-TV viewing behaviours occurring most during programming which required less visual attention, such as advertisements. This effect was greatest amongst children (Schmitt, Woolf, & Anderson, 2003). More recently, the mobile functionality of newer screen-based media devices, included smartphones and tablets (e.g. iPads), has increased the accessibility to competing screen-based behaviours and has created a multi-screen world (Phalen & Ducey, 2012), where adolescents report using multiple screens to facilitate filtering out of unwanted content, including advertisements (Jago, Sebire, Gorely, Cillero, & Biddle, 2011).

Within this contemporary screen environment, differences exist in the way adolescents, young adults, and older adults (⩾30 years) use and interact with media. Recent data suggest that young adults use social media in a similar fashion to adolescents, while older adults interact with social media differently (Lenhart, Purcell, Smith, & Zickuhr, 2010). This difference in media use is consistent with the notion of a generation digital divide, whereby adolescents and young adults feel more comfortable using and interacting with digital media compared with older adults (Vie, 2008). Emerging adulthood, defined as 18–25 years (Padilla-Walker, Nelson, Carroll, & Jensen, 2010), is evolving as an important age group with respect to screen-based media use. It is characterised by greater flexibility in schedules and lack of parental supervision, which is thought to contribute to the high rate of video game use in this age group (Anand, 2007). Given that younger generations who have grown up in an environment saturated with screen-based media interact and use screen-based media differently compared with older generations, it is reasonable that the effects of screens on health-related behaviours may differ between generations and should therefore be investigated separately.

As technology increasingly allows for greater control over exposure to advertising, and youth divide their attention between multiple media devices simultaneously, it seems timely to review the evidence on the non-advertising effects of screen-based activities on dietary intake. As such, a review of laboratory-based, experimental studies was conducted to determine the non-advertising effects of screen-based sedentary behaviours on energy intake in normal and overweight children, adolescents, and young adults. A systematic review of randomised controlled trials (RCTs) and quasi-experimental studies was undertaken according to the PRISMA Statement (Transparent Reporting of Systematic Reviews and Meta-analyses) (Liberati et al., 2009).