Obesity and Physical Inactivity: The Relevance of Reconsidering the Notion of Sedentariness

Chaput JP, Tremblay A. Obesity and Physical Inactivity: The Relevance of Reconsidering the Notion of Sedentariness. Obes Facts. (2009)2(4):249-254.

updating imageThe 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.

My comments: Traditionally, the treatment of obesity has focused on two primary components which are dietary intake and energy output; there are both good and bad reasons for this that I’ll address in a future article or research review but the fact remains that those two factors tend to represent the things we have the most control over (e.g. we can’t do anything about genetics, or about what mom did while she was pregnant).  I tend to think I’ve spent enough time on the site talking about diet that I needn’t get into it here so I’m going to focus on the activity end of things.

Now, as discussed in Metabolic Rate Overview as well as The Energy Balance Equation, there are 4 primary components on the energy out side of the energy balance equation: Basal metabolic rate (BMR), Thermic effect of Food (TEF), Thermic Effect of Activity (TEA) and Spontaneous Physical Activity/Non-Exercise Activity Thermogenesis (SPA/NEAT).  The two I’m going to focus on relative to today’s research review are the last two, a recent separation whereby formal exercise and all other daily activities have been separated out.

Now, traditionally obesity treatment has also focused on the exercise end of the equation but there have always been a few problems with this.  Perhaps the largest relative to what I want to talk about today (and I’ll be doing a very thorough article at a later date on this so please be patient in the comments) is that the amount of exercise that is or can usually be done is actually fairly trivial compared to the rest of the day.

That is, the hour someone might spend engaged in exercise is still pretty small compared to what’s happening the other 23 hours of the day.  And, as many have found out by using tools such as the Bodybugg/GoWear Fit, small changes during the majority of the day (e.g. getting up every so often during the day to walk around at work for 8 hours) end up having a far larger impact on daily energy expenditure compared to the hour of exercise they might do.  As many have also found, being very inactive for those same 8 hours (e.g. jockeying a computer desk) doesn’t burn many more calories than laying in bed.

Which is all a very long introduction to today’s paper which looks in some detail at two of the major changes in modern life that contribute to our overall ‘inactivity’ during the day: sleep and what the researchers decided to call knowledge based work (KBW).  Sleep is fairly explanatory but, by KBW, they are referring to things such as school, jobs involving thought and concentration and even potentially video games.  Basically anything where you’re sitting on your ass for most of it but having to involve your brain rather intently.

And while both activities fall under the heading of ‘inactivity’ (in that you burn very few calories during either of them), they actually end up having not only different but diametrically opposed effects on the potential for weight gain and obesity.  Basically, just saying that ‘inactivity causes weight gain’ is simplistic and, as it turns out, incorrect.  The type of inactivity is relevant here.

In the case of sleep, and there has been a tremendous amount of literature in this regards in recent years, it’s turning out that sleep deprivation does rather horrible things not only for overall health but for weight gain and obesity risk.  Sleep deprivation tends to decrease leptin level (removing the tonic ‘block’ that leptin exerts on appetite/hunger) and raise level of ghrelin (the only hormone shown to directly stimulate hunger in humans).   I discuss both hormones in detail in the series on Hormones of Bodyweight Regulation but the end result of such a shift will be an increase in hunger/appetite along with a negative effect on calorie partitioning.  Hormones such as cortisol, thyrotropin hormone (involved in thyroid function) and others are also impacted positively by sufficient sleep and negatively by too little sleep.  As the authors state:

Hence the beneficial effect of sleep go well beyond its role in the restoration and maintenance of tissue structure and function…Despite the low energy cost of sleep, population studies have repeatedly shown that a short average duration of sleep is associated with excess body weight…recent research evidence showed that an average nightly sleep of 7-8 h in adults is associated with a lower risk of obesity, type 2 diabetes, coronary heart disease and all-cause mortality.

Hard to get much clearer than that.  Basically, despite the unbelievably low caloric cost of sleeping (usually around 1 cal/min), the indirect impact is massive in terms of the benefits for getting enough sleep and harm for not.

Moving on to the other topic of the paper we get to KBW, again referring to activities such where you’re sedentary but engaged in large amount of mental activity.  The paper mentions work, school, even video games and computer ‘chatting’ (you Facebook people know who you are) and other related activities as potential examples of KBW.

And, as you might expect, while similarly sedentary like sleeping, the impact of KBW on appetite and body weight regulation tend to be rather negative.  The brain, unlike skeletal muscle, can’t use fat for fuel and studies have shown that intense thinking can screw blood glucose levels; this is relevant as some work shows that falling or lowered blood glucose can stimulate hunger.  And usually for junkier food (which is invariably found in large amounts in the work space).

Studies have found that even short bouts of intense KBW can increase total energy and fat intake as well.    In one, for example, females were assigned to a 45-min mental work session and then provided an ad-lib buffet.  Despite only burning 3 extra calories during the task, the KBW group ate 229 more calories compared to a group that only rested.  In the long-term, this adds up big time.

And while it hasn’t been studied directly, the researchers question whether such things as video games and Internet chatting might be similarly stimulatory of appetite (and let’s be honest, is anybody eating non-junk food when they play WoW).  The amount of time spent watching Tv is a known risk factor for obesity in children, increasing the intake of high-energy density tasty foods; whether this is related to the same mechanism as KBW such as work or studying is currently unknown.

Finally, it’s worth mentioning that Tv and computer involvement is often done late at night and this can interrupt sleeping patterns (the constant influx of photos into the eyes makes it harder to get to sleep).  So there’s a potential double whammy.

Summing up: So that’s that, a quick look at two different types of ‘inactivity’ that end up having diametrically opposed effects on the risk for weight gain, obesity and other health risks. Those two are sleep, perhaps the most sedentary activity of all (unless you get lucky) and knowledge based work (KBW).

Getting sufficient sleep, something that is becoming harder for many to do (by choice or life requirement) is a key aspect of not only overall health but limiting obesity risk.  With good sleep hygiene and habits (e.g. get off the computer earlier, go to bed a bit earlier every night), this is at least within the realm of some people’s control.

The issue of KBW is tougher as folks have to make a living and many jobs involve long hours of KBW (often in an environment where nothing but crappy food is available).  Clearly quitting your job and sleeping all day, while attractive, isn’t an option for most.  At least being aware that intense bouts of KBW can screw with blood glucose and appetite may help with finding strategies around it.

Keeping better snack foods handy to stave off hunger following such work efforts would be one strategy, I have to wonder if a small amount of carbohydrate during the activity would help to stabilize blood glucose.  Perhaps Gatorade can come up with a ‘Conference Call Gatorade XXXtreme’ version of their drink.  Yes, XXXtreme with three X’s.

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About Lyle McDonald 10 Articles

Lyle McDonald has been interested in all aspects of human performance physiology since becoming involved in competitive sports as a teenager. Pursuing a degree in Physiological Sciences from UCLA, he has devoted nearly 20 years of his life to studying human physiology and the science, art and practice of human performance, muscle gain, fat loss and body recomposition.


Lyle has been involved, at various levels of success in competitive sports since his teens. Starting with triathlon, he spent altogether too many hours on his bike during college. Becoming involved with inline skating at the same time led him to compete for several years until he burned himself out with chronic overtraining. Many years passed until he decided to return to speed skating and move to the ice. He moved to Salt Lake City Utah to train full time at the Olympic oval, he is currently still there training with his coach Rex Albertson attempting to make the US National team or beyond.


Lyle has written for the print magazines (Flex and the now defunct Peak Training Journal), too many online sites to mention (including Cyberpump, Mesomorphosis, MindandMuscle, ReadtheCore) and has published 5 books on various aspects of exercise and diet.


Over the years, in addition to working with the general public, Lyle has worked primarily with endurance athletes, a few powerlifters, and some bodybuilders. Through his books, articles and his forum, he has helped thousands lose fat, gain muscle and get stronger or perform better.

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