Although obesity research has traditionally focused on the role of diet and exercise, the unique contribution of sedentary behaviour (e.g. sitting or lying down) has received increasing attention in recent years. In particular, television (TV) viewing has been frequently associated with weight gain in both children and adults independent of other risk factors including baseline BMI and physical activity levels(Reference Tremblay, LeBlanc and Kho1, Reference Thorp, Owen and Neuhaus2).
Like TV watching, sleep is an activity characterised by prolonged periods of reduced energy expenditure. Yet accumulating evidence suggests that adequate sleep protects against obesity, while short sleep duration is prospectively associated with increases in both total and abdominal adiposity in adults and children(Reference Patel and Hu3, Reference Chaput and Tremblay4). These contrasting lines of evidence suggest that if an individual is planning to spend an afternoon on the couch, they are better off asleep than watching TV. While the above may seem like an odd public health message, it is nonetheless supported by a growing body of research suggesting that TV viewing and sleep have contrasting effects on energy balance and weight maintenance.
TV viewing burns energy at a slower rate than most other waking activities, which may initially seem like the most probable mechanism explaining its association with excess weight gain(Reference Tremblay, LeBlanc and Kho1, Reference Thorp, Owen and Neuhaus2). However, a meta-analysis has reported only minor associations between TV viewing and moderate or vigorous physical activity(Reference Marshall, Biddle and Gorely5) in children and youth, suggesting that TV viewing does not displace high-intensity exercise in this age group. Further, it has been reported that the relationship between TV viewing and adiposity is not mediated by physical activity energy expenditure(Reference Thorp, Owen and Neuhaus2). It is worth noting that it is also entirely possible for an individual to accumulate large amounts of TV time while still exceeding physical activity guidelines. Although the relationship between TV viewing and energy expenditure is not yet conclusively understood, most available evidence suggests that it may be energy intake, rather than expenditure, that largely accounts for the relationship between TV viewing and weight gain.
TV viewing has been linked to increased food intake in both prospective and intervention studies. This may be partially due to exposure to food advertisements, which often promote unhealthy dietary habits, and may prime individuals for future food intake. A recent intervention study by Harris et al. (Reference Harris, Bargh and Brownell6) has reported that exposure to food advertisements increased subsequent food intake by roughly 30 and 45 % in adults and children, respectively. TV viewing also provides opportunities for snacking, and is associated with an increased intake of high-energy foods and passive overconsumption(Reference Thorp, Owen and Neuhaus2). Intervention studies that impose a reduction in TV viewing among children have consistently reported reductions in body weight(Reference Tremblay, LeBlanc and Kho1), which may be moderated through reductions in food intake(Reference Epstein, Roemmich and Robinson7). These findings suggest that TV viewing has a relatively strong positive association with food intake in both adults and children.
As with TV viewing, people burn energy slowly while asleep. Reducing time spent sleeping could therefore theoretically provide an individual with more opportunities for increased energy expenditure. Nevertheless, some evidence suggests that partial sleep deprivation may actually be associated with decreased energy expenditure through fatigue-related reductions in physical activity and lowered body temperature(Reference Patel and Hu3). This remains controversial, however, as more recent studies have found little evidence linking partial sleep deprivation to changes in total energy expenditure, RMR or physical activity(Reference Chaput and Tremblay4). Thus, as with TV viewing, available evidence suggests that energy expenditure is not the primary mechanism linking insufficient sleep with increased adiposity.
Current evidence suggests that sleep duration is negatively associated with both acute and chronic food intake. Sleep restriction is known to increase food intake in both human subjects and animal models, and seems to predispose individuals towards increased intake of energy-dense foods that are high in fats and carbohydrates(Reference Chaput and Tremblay4). These effects on food intake are probably related to changes in homeostatic (e.g. hormonal) and/or hedonic (e.g. reward-seeking) feeding behaviour(Reference Patel and Hu3, Reference Chaput and Tremblay4). Insufficient sleep may increase the homeostatic drive to eat, as short-duration sleepers are known to have increased levels of ghrelin, reduced levels of leptin and altered glucose homeostasis(Reference Patel and Hu3, Reference Chaput and Tremblay4). Short sleep duration may also increase the rewarding value of food, which suggests that food intake could also be increased through non-homeostatic mechanisms(Reference Chaput and Tremblay4). Finally, reduced sleep may simply offer individuals increased opportunities for energy intake(Reference Patel and Hu3, Reference Chaput and Tremblay4). This impact may be especially strong when extra waking hours are spent watching TV, which may further stimulate food intake(Reference Chaput and Tremblay4). Collectively, this evidence suggests that inadequate sleep may have a substantial impact on energy intake, and thereby energy balance and body weight.
The above evidence suggests that TV viewing and sleep exert opposing influences on energy balance and body weight. It is also worth noting that the relationships of both sleep and TV viewing with obesity appear to be stronger in the paediatric age group(Reference Thorp, Owen and Neuhaus2, Reference Patel and Hu3). TV viewing tends to stimulate food intake, while an obesogenic environment exacerbates this problem with easy access to energy-dense and palatable foods. In contrast, the activity of sleeping is ‘satiating’ from biological and environmental perspectives since it reduces the drive to eat, opportunities for food intake, and exposure to external food-related cues. Although speculative, it is plausible that a few hours of napping on the couch could have a vastly different (and more positive) impact on weight maintenance than an equivalent amount of TV viewing. This raises an obvious question: if you are concerned about your body weight, is it better to sleep through your favourite TV show rather than watching it?
It is perhaps time that clinicians urge their patients to not only reduce their daily amount of TV viewing, but to also replace that TV time with a good night's sleep. Interventions that focus on increasing sleep time or reducing TV viewing may prove easier to implement than those focused specifically on diet or exercise. Available evidence already suggests that reducing TV time is an effective means of reducing body weight in children and youth(Reference Tremblay, LeBlanc and Kho1, Reference Epstein, Roemmich and Robinson7), and initial reports have suggested that increasing sleep may improve mood and help reduce food cravings among obese adults(Reference Chaput and Tremblay4). Reducing TV viewing and/or getting adequate sleep require little in the way of resources or expertise, and may therefore be more sustainable than more traditional interventions focused on diet and exercise. If having a good night's sleep truly is better for your weight than watching TV, this would be a lifestyle modification which may be substantially easier to implement than adopting a new diet or exercise routine. This change of focus is certainly worth consideration, right after a short nap.
Acknowledgements
T. J. S. is supported by Doctoral Research Awards from the Canadian Institutes of Health Research and the Canadian Diabetes Association, as well as an Excellence Scholarship from the University of Ottawa. J.-P. C. holds a Junior Research Chair in Healthy Active Living and Obesity Research. The contribution of the authors is as follows: T. J. S. and J.-P. C. conceived of the topic of the manuscript; T. J. S. wrote the first draft of the manuscript; J.-P. C. provided critical comments and suggestions. Both authors approved the final version. The authors declare that there are no conflicts of interest.
