More evidence on physical activity and obesity

Tim Olds has written a nice article about the bogus controversy about whether burning off calories helps people lose weight.

People don’t seem to be exercising more or less than they used to. Studies show little historical change in leisure time physical activity. But there have been big declines in occupational physical activity as workplaces have become automated and the service economy replaces manufacturing and farming.

A study looking at work-related physical activity over five decades showed declines of about 500 kilojoules a day in energy expended on the job by US workers. Another spanning 45 years suggests the time women spent on domestic chores required about 1,000 kilojoules less each day in 2010 than they did in 1965.

Declines in energy expenditure of this magnitude are more than enough to account for historical increases in fatness.

He even dares to tell the truth about calorie consumption...

In 2008, one of my graduate students, Jo Stevenson, systematically reviewed studies reporting the energy intake of children. She found 2,148 reports dating back to 1856, covering 425,905 mainly European, North American and Australian children.

There was a consistent decline in energy intake of school-aged kids from 1920 onwards, at the rate of about 2% to 3% per decade, flattening out in the late 1990s. By 2000, kids were eating about 20% less than they did in 1920. Even conservatively allowing for under-reporting by fatter kids and methodological differences, the decline was still of the order of 1% to 2% per decade. Unfortunately, this research wasn’t published so I can’t link it here.

The evidence that adults are eating more may also be very suspect. Data from the periodic National Health and Nutrition Examination Surveys (NHANES) in the United States are often used to indicate upward trends in energy intake. But Blair’s team has previously convincingly argued – in a peer-reviewed article published in a well-respected journal – that these trends are likely to be artefacts resulting from changes in research methodology, and that dietary data are inherently unreliable anyway.

So historically, the evidence is that it ain’t the meat it’s the motion.

It's not often that The Conversation publishes a sensible article so do read it.