Obesity and physical inactivity: the relevance of reconsidering the notion of sedentariness

Abstract

The population statistics of most countries of the world are indicating that industrialization and computerization have been associated with an increase in sedentariness and more recently with a significant shift from healthy weight to overweight. In general, this change in the overweight/obesity prevalence is attributed by health professionals to suboptimal diet and physical activity practices. However, recent data raised the possibility that excess weight gain might also be the outcome of changes imposed by our '24-hour', hectic lifestyle. Parallel to an increase in body weight, one has observed a reduction in sleep time and an increase in knowledge-based work (KBW) that appear as a growing necessity in a context of economic competitiveness and globalization. Sleep and cognitive work both exert a trivial effect on energy expenditure and may thus be considered as sedentary activities. However, their respective effect on energy intake is opposite. Indeed, an increase in the practice of the most sedentary activity, i.e. sleep, is associated with a hormonal profile facilitating appetite control whereas KBW appears as a stimulus favoring a significant enhancing effect on food intake. Television viewing is another example of sedentary activity that has been shown to increase the intake of high-density foods. These observations demonstrate that the modern way of living has favored a change in human activities whose impact goes well beyond what has traditionally been attributed to a lack of physical exercise. Therefore, we will need to reconsider the notion of 'sedentariness' which includes several activities having opposing effects on energy balance.

Fig. 1

Potential mechanisms by which sleep loss may predispose to obesity. Adapted from Patel and Hu [32].

Fig. 2

Cortisolemia observed while performing a reading-writing activity for 45 min and spontaneous energy intake in an ad libitum meal following the task in female students categorized by their degree of mental workload. Note: A long reaction time reflects a high perceived mental workload. Data are expressed as mean ± SD. *Significantly different from students presenting a short reaction time, p < 0.05. Adapted from Chaput et al. [47].