Energy in vs energy out

The rise in obesity is due to many factors but the root cause is the imbalance between energy in (what we consume) and energy out (mainly burned through physical activity). A lot of attention has been paid to the types of food we eat, but data shows that average energy intake may actually be declining. This suggests that physical activity must have been declining even faster. And walking has been declining the most. Mainly due to cars.

Walk this way (instead of driving)

As car ownership increases, many journeys that would once have been made on foot are being replaced by car travel. Each year, a greater proportion of the time spent travelling is by car, and the distance travelled on foot declines.

A study published in August 2007 showed that main car drivers walk only half the distance and for half the time of adults in non-car owning households. This is a deficit of 56 minutes of walking every week for these drivers, relative to adults in non-car households. As the study's authors say,

"Over a decade we calculate that this could lead to a weight gain of more than 2 stones...for most obese adults their weight gain has accumulated over many years. Small energy imbalances on a daily basis can lead to major weight gain over a decade and more, and our calculations indicate that this decline in walking is in itself enough to account for much if not all of the recently observed upsurge in obesity."

Source: Adrian Davis, Michael Fergusson & Carolina Valsecchi, Unfit for Purpose: How car use fuels climate change and obesity (London, Institute for European Environmental Policy, August 2007