Monday, May 30, 2011

Are we obese 'cause we sit all day long?

That was one of the cases put forth by Dr. Bob Ross during our Forks vs. Feet debate.

He had discussed an as of then unpublished study that concluded that due to changes in occupation-based physical activity, we were all on average burning 100 fewer calories per workday, and that those no longer burned calories have caused us to become obese.

Well, the paper was just published and I had a gander.

Now I do think there are weaknesses to the analysis, in that this study of theoretical energy expenditure lost at work doesn't in fact provide a picture of total daily energy expenditure. Meaning that the authors have no idea what the study subjects energy expenditures were like when they weren't working. That's problematic for a few reasons.

Firstly it's problematic because it's possible that if you take away 100 calories burned through physical labour, perhaps you'll put them back elsewhere. What I mean to say is that in children we've seen evidence for the existence of an Activitystat whereby kids who exercise more at school do less at home and vice-versa. Given such behaviour has been demonstrated to exist in children, I don't think it's an impossible stretch to wonder if it also occurs in adults, especially since we're talking about just 100 calories per day. And even if it didn't translate to intentional exercise, couldn't more sedentary jobs lead to more fidgeting? More fidgeting would mean more Non-Exercise Activity Thermogenesis. Dr. Levine suggests purposeful NEAT can add up to 500-1000 calories a day, how difficult would an unconscious 100 be?

Secondly it's problematic because doubly-labeled water studies suggest that at least between 1983 and 2005, in study populations from Holland and North America, daily energy expenditures haven't changed. Yet in both Holland and North America during that same time period obesity rates have risen dramatically and presumably, we're working progressively cushier jobs.

Thirdly it's problematic because in doubly labeled water studies that look at total daily energy expenditure of folks living in developing nations vs. developed nations, for instance subsistence farmers in Nigeria vs. urban Chicagoans, there's been no difference in calories burned, and that total daily calories burned in both populations didn't correlate with weight. I would certainly imagine that being a subsistence farmer in Nigeria would be quite physically demanding work.

Lastly, in a massive study of 98 doubly labeled water studies representing 183 cohorts including 14 from countries with low or middle "human development index" (and hence more likely to have physically demanding jobs), again there was no difference in total daily energy expenditures.

But even putting aside those concerns, I think the paper's conclusions are telling in regard to the Forks vs. Feet debate.

Clearly both forks and feet are thermodynamically implicated in obesity.

In one corner, taking this paper to be true (true despite the fact doubly labeled water studies that actually measure total daily energy expenditures suggest otherwise), we've now got 100 calories a day we're not burning due to less physically demanding jobs.

In the other corner we've got energy intake data suggesting that since 1970, based off of plate-waste disappearance data, adults are consuming 500 more calories daily now as compared with 1970.

Basically we're looking at a 600 calorie surplus. 100 from fitness and 500 from food. Put another way, our modern caloric excess is 83% food and 17% fitness, not exactly a home run for the Feet camp, but damn close the 80/20 rule I tend to believe is true.

Church, T., Thomas, D., Tudor-Locke, C., Katzmarzyk, P., Earnest, C., Rodarte, R., Martin, C., Blair, S., & Bouchard, C. (2011). Trends over 5 Decades in U.S. Occupation-Related Physical Activity and Their Associations with Obesity PLoS ONE, 6 (5) DOI: 10.1371/journal.pone.0019657

Wilkin, T., Mallam, K., Metcalf, B., Jeffery, A., & Voss, L. (2006). Variation in physical activity lies with the child, not his environment: evidence for an ‘activitystat’ in young children (EarlyBird 16) International Journal of Obesity, 30 (7), 1050-1055 DOI: 10.1038/sj.ijo.0803331

Luke, A., Dugas, L., Ebersole, K., Durazo-Arvizu, R., Cao, G., Schoeller, D., Adeyemo, A., Brieger, W., & Cooper, R. (2008). Energy expenditure does not predict weight change in either Nigerian or African American women American Journal of Clinical Nutrition, 89 (1), 169-176 DOI: 10.3945/ajcn.2008.26630

Lara R Dugas, Regina Harders, Sarah Merrill, Kara Ebersole, David A Shoham, Elaine C Rush, Felix K Assah, Terrence Forrester, Ramon A Durazo-Arvizu, & Amy Luke (2011). Energy expenditure in adults living in developing compared with industrialized countries: a meta-analysis of doubly labeled water studies The American Journal of Clinical Nutrition, 93 (2), 427-441 : 10.3945/​ajcn.110.007278

Westerterp, K., & Speakman, J. (2008). Physical activity energy expenditure has not declined since the 1980s and matches energy expenditures of wild mammals International Journal of Obesity, 32 (8), 1256-1263 DOI: 10.1038/ijo.2008.74

Swinburn, B., Sacks, G., & Ravussin, E. (2009). Increased food energy supply is more than sufficient to explain the US epidemic of obesity American Journal of Clinical Nutrition, 90 (6), 1453-1456 DOI: 10.3945/ajcn.2009.28595

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  1. There is no significant change in daily energy expenditures shown in previous studies because the change is within the error of measurement about 50-100 kcal. Otherwise, the conclusions are speculative for the reasons you evoqued. I am also agree about the contribution of Fork-Feet in the weight management to 80-20. Can't be disagree this morning. Grrh! LOL

  2. What a crazy day!

    The sun is shining in Ottawa and we don't disagree!

    Have a good one,

  3. I don't fundamentally disagree with the conclusion, but which self-report energy intake studies are you referring to? I ask because I had to find a lot for my comprehensive exam paper, and was surprised at just how equivocal the results are in both Canada and the US - about half the studies show a minor increase, and half show no change whatsoever. Not that I believe that's the "truth", but it's surprisingly hard to find evidence for changes in exercise or diet when looking at historical self-report data.

  4. Thanks Travis,

    You're right, self-reported data's awful and after reading your comment, I re-read the Swinburn study and it was an estimate and not a measurment. There are Canadian estimates too based off plate-wasted adjusted available calories which very clearly demonstrate a rise, but don't necessarily reflect consumption (perhaps we're just wasting more food).

    I'll also ammend the post to reflect this.


  5. Anonymous10:42 am

    How does a physically active job compare to a sedentary job not just in the calories burned, but in what food is eaten?

    Theory: doing a physical job affects what you eat.

    if you're a blacksmith or a construction worker you're not likely to snack on the job. More likely you'll stop work for a set mealtime.

    If you're an office worker, you're more likely to have snacks available, maybe even muffins and coffee served in meetings. People eat at their desks and that means snacks as well as meals. Non physical work is more likely to include food based activities like business restaurant lunches or special dinners , which are often high calorie.

    Theory Part 2: A physical type of commuting affects what you eat.

    Whether you're commuting to a physical or a sedentary job, these days people drive with double-doubles and donuts to consume on the way.
    Even if walking or biking doesn't burn a lot of calories, people are less likely to eat or drink while they're walking or biking.

    Re 80% food; 20% feet:
    As well as burning calories, increasing Feet (physical work or commute), probably also has a side effect of decreasing Food.

    In discussing physical vs sedentary work:

    ? % Feet (calories burned) /

    ? % Feet affected Food (ie calorie reduction precisely BECAUSE of the environment of "Feet" (physical) work and/or commute) /

    ? % Food factors not affected by work or commute

    Maybe 80 % food / 20 % feet can be described more fully by:

    60% Food / 20% Feet-affected -Food / 20% Feet

    I have no idea how that theory could be tested or measured!

  6. Anonymous11:31 am

    I think there are a lot of small cumulative calories expenditures that have disappeared. For example, I remember a much colder thermostat temperature. And as said already, there are many more opportunities to eat during the day, beginning in childhood.

  7. Anonymous 10:42 AM - On the other a physical job or commute may make one more hungry and therefore eat more. I know I am hungrier when I bike to work (45 minutes each way). I often need an additional snack or a bigger one than usual.

  8. Great post. It makes intuitive sense that the sharp rise in obesity in the past 20 years can't be explained primarily by energy expenditure changes but it certainly can be explained primarily by changes in food intake. It is a lot easier to add 500 calories to your food intake than it is to change your daily energy expenditure by 500 calories. Portion sizes are much larger than they were in the 80's, and as a solid body of evidence shows, people finish what is on their plate.

  9. Anonymous4:14 pm

    Why Americans are getting heavier

  10. Anonymous5:44 pm

    "Fork vs Feet"

    Back then: forks and feet
    Now: hands and seat!

  11. Anonymous5:48 pm

    Rhodia - Quite true.

    Anon 10:42

  12. I think in the Fork/Feet debate the part that stood out for me was "i know the calories i can consume in 3 minutes, are likely going to exceed the calories i burned in my exercise"

    Exercise helps health-wise but as far as actual weightloss, it's more about diet. Most over-weight people cant burn more calories than they consume.

    I think the whole -people are obese because they have desk jobs and dont move enough is rubbish..there are plenty of obese landscapers/farmers/construction workers etc

    You can burn calories all day long, if your eating 3000+ calories worth of fast food/junk food a day you will still get fat. And likewise if you only eat 1200 calories a day, everyday of your life, your likely not an overweight person.

    I just think weightloss will always be primarily based on diet. physically we can't compete with the amount of fat and calories in most pre-package or fast foods.

  13. To add something to the fork v food debate which I haven't yet seen mentioned. (sorry about the links, you'll have to cut and paste)

    Firstly, an article fron the NYT earlier this year, looking at exercise and weight loss. They discuss research into the 'afterburn effect', the process by which high intensity exercise continues to 'burn calories', long after the exercise has stopped.

    Secondly, have a look at the documentary "10 things you need to know about losing weight" screened in the UK on the BBC. The link below is to part one, the other 4 parts can be accessed from there. Amongst other things, Dr Micheal Mosley the medical journalist and presenter tests the theory out.

  14. Anonymous12:42 pm

    Couldn't it just be that people are becoming less mindful about their bodies? If you burn more calories, you should be more hungry and therefore eat more. If you burn less calories you should be less hungry and eat less. It shouldn't really matter if we burn 100 less calories per day.

  15. Its interesting because placement during the day and the food choices made available at the local, the implications show up all the way down the line
    Children in school settings who get calorically dense food made available choose it over leaner options