Thursday, May 26, 2011

A weighty matter

I think we all recognise that over the past few decades, the average person has become a more sedentary creature. It's nice then to get some data to back it up.

Researchers have looked at US data on occupations and physical activity and shown that, since the 1960's, the estimated mean daily energy expenditure due to the job we do has dropped by more than 100 kcal.

While this is US data, it should inform the obesity debate in this part of the world. A recent report from the European Commission found that 23% of Irish adults are considered obese. While an OECD report in 2010 found that Ireland was the second most overweight country in Europe.

The researchers used data from the US Bureau of Labor Statistics and from the US National Health and Nutrition Examination Surveys.

The findings suggest that this significant reduction in calories expended daily accounts for a "significant portion of the increase in mean US body weights for women and men".
Figure 1. Service, goods producing and agriculture jobs in US from 1960 to 2008.

The proportion of Americans in 'service' jobs as opposed to manufacturing, construction and agricultural jobs has increased hugely since 1960. (Fig 1)

As you might expect, the amount of physical activity involved in something like financial services or teaching is much less than that required for agricultural or construction (the most energy intensive) jobs (Fig 2). Hence, the fall in average daily energy expenditure.
Figure 2. Estimated median and range of physical activity intensity (METs) as well as the estimated caloric expenditure of each occupation.

Employment is, of course, not the only factor involved here. For example, the authors note that since 1960, the amount of energy spent on housework has 'greatly decreased' for women and slightly increased for men.

Diet and exercise probably remain the two most important factors which we can influence but it is interesting to see that the job we do also influences our likelihood to be overweight.

Things like how we travel to work, whether we use stairs or not were not considered in the study and it is unlikely to be as clearcut as we might like to think.

The results come as Safefood Ireland launch a two-year Stop the Spread campaign to encourage Irish people to measure their real waist size.

Safe Food say that only 38% of adults believe they are overweight. In fact, 66% of the public are overweight. The other 285 just don't know it or are in denial!

Church TS, Thomas DM, Tudor-Locke C, Katzmarzyk PT, Earnest CP, et al. (2011) Trends over 5 Decades in U.S. Occupation-Related Physical Activity and Their Associations with Obesity. PLoS ONE 6(5): e19657. doi:10.1371/journal.pone.0019657


Anonymous May 27, 2011 at 11:18 AM  

100 kilocalories?

Eoin Lettice May 27, 2011 at 12:49 PM  

Yes, I think so. Have made the change.


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