Are More People Exercising Even As Obesity Rates Climb?

Are More People Exercising Even As Obesity Rates Climb?

How can this be? Reporters tell us that Americans are exercising more while obesity rates are increasing. It was the latest National Health Interview Survey data that prompted reporters to write such headlines. Between 2006 and 2017, the percentage of adults who say they meet aerobic exercise guidelines went from 41% to 53%. The numbers for people meeting guidelines for both aerobic and strength activities are considerably smaller.

At the same time, self-reported obesity rates went from 26% to 31%.

Self-Reported Mishmash

It helps to remember that this nonsense comes entirely from self-reported data. Especially when we tell people that they ought to be exercising more, should we be surprised that they report more exercise than they actually do? Likewise, people can hardly miss dire messages about how bad obesity is. So it’s completely unsurprising that people think of themselves as lighter and taller than they really are.

Ask people how tall and heavy they are and you get an obesity rate of 31%. But when you weigh and measure them, the prevalence is 40%.

Difficulty Correlating Self-Reports of Physical Activity

Last year, Miriam Wanner and colleagues did much to explain this problem. With a study published in IJO, they examined both self-reported and objectively measured physical activity. They found consistent relationships between objective measures of physical activity and obesity. More active individuals are less affected by overweight and obesity.

But for self-reported activity, those relationships were not robust. Self-reported data is simply less reliable. It’s subject to more bias, and that bias can be unpredictable.

Then There’s Occupational Activity to Consider

One final note is that occupational activity is at least equally important. Earlier this year, Tim Church and Corby Martin reminded us that “formal exercise plays a very small role in total daily physical activity.” And occupational physical activity levels have dropped so low that they are likely playing a significant role in rising obesity prevalence.

In other words, this is a puzzle with many pieces. Even if self-reports were reliable (they aren’t), leisure-time exercise doesn’t even come close to telling the whole story. Active lives are defined both by what we do at work and what we do at home and play.

To solve this puzzle, we need all the pieces. Not just a few clues that leave us guessing.

Click here and here for more data from the National Health Interview Survey. For further perspective, click here.

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July 2, 2018