Preventive Medicine Column

Dr. David L. Katz

One of the higher profile medical stories of the past week was the news that work is increasingly workless- in the physical sense, that is.  Physics defines work as force times distance, and we apply ever less of the former, as electrons traverse ever more of the latter on our behalf.

Specifically, the study published in PLoS One, and the media coverage published everywhere else, tell us that the average man expends roughly 142 fewer calories per day at work, and the average woman expends 124 fewer, based on an analysis of Department of Labor statistics from the 1960s to 2008.

The theoretical importance of this finding is that it helps to explain the obesity epidemic, and a bit of number crunching quickly shows why.  Assume that everything other than energy expenditure at work stayed constant over the past 4 decades (nonsense, of course, and we’ll come to that shortly- but go with it for now).

A man burning 142 fewer calories each of roughly 240 work days per year would burn just shy of 34,000 fewer calories annually.  Using the standard, if somewhat inaccurate, 3500 calories per pound of body fat gained or lost, that translates to about 9.7 lbs of weight gain in just one year!  A comparable calculation with the woman’s 124 fewer calories burned translates to 8.5 lbs.

That this one finding, if even remotely accurate, could account for much of the modern obesity epidemic all on its own goes a long way toward demonstrating how truly unmysterious the epidemic is!  We really don’t need a lot of exotic theories to account for rampant obesity in the modern age.  We just need what we have: a massive shift in energy balance.

That we’re burning fewer calories at work is about as surprising as a report telling us we’re using more cell phones.  And, in fact, the two are separate halves of the same, obvious truth.  We have ever more technology in our lives doing what muscles used to do at work, and at play.  This is another one of those times when a careful analysis of a lot of data demonstrates what the average person would quickly conclude merely by not living under a rock.

And this obvious truth about energy expenditure is just part of an equally obvious, larger truth- also accessible to all with an above-rock-bottom view of the world.  We are eating more, too.

You may already know my refrain on this topic: throughout all of human history until very recently, calories were relatively scarce and hard to get and physical activity was unavoidable.  We have devised a modern world in which physical activity is increasingly scarce and hard to get, and calories are unavoidable.

Nothing relevant to energy balance has stayed constant over the time span in question!  The number of processed foods has increased by tens of thousands.  The use of food chemicals has gone up.  Portion sizes have increased.  Fast food has become a fixture.  Time and knowledge for food preparation have gone down.  Factory farming has emerged, and surged.  The use of hormones in animal husbandry has expanded.  The Internet was invented.

The proximal explanation for epidemic obesity is less use of our feet, less prudent use of our forks.  The root explanation is everything about modern living that makes it modern.  Workless work is an example.

What, then, are the take-away messages from this study, and the media attention to it?

First, the obesity epidemic is hard to fix, but not hard to explain.  We tend to act as if the first requires the second, and so keep doing studies to re-verify the obvious.

Second, since obesigenic influences have been engineered into the structure of the work day, it is indeed silly as well as wrong to blame the victims of rampant obesity.  The amount of physical work demanded of you by your job is not a matter of will power.  It is a fundamental change at the societal level, far larger than the personal choices and personal responsibility of any individual employee.

Third, the fact that the obesity epidemic is easily explained does not mean that every individual’s struggle with weight is quite so clear.  There are cases of extreme susceptibility to weight gain, and unusual resistance to weight loss- and I’ll address that next week.

Fourth, if we engineered the causes of obesity into the typical day and are reaping the consequences, logic suggests that we should engineer the remedy back into daily routine if we hope ever to reap the reward.  Our recently launched ABE for Fitness program ( is a timely example; hourly 5-minute activity bursts it is designed to fit into a work day would allow the average adult to burn 100 calories or more each day.

Work has been cut out of our play, and our work.  We now have our work cut out for us: engineering it back in!







Dr. David L. Katz;