Megan McArdle points to a Time Magazine piece on exercise. Exercise, it turns out, won’t make you thin.
I’ll try to limit how much I point out that the notion of losing weight simply by exercising had to be questionable to anyone with spreadsheet program and even a moderate desire to verify conventional wisdom. The numbers just don’t add up. The simulations just don’t bear any resemblance to reality.
What’s important is that this is entering the intellectual ether and has some chance of influencing policy and thought on the obesity epidemic. There isn’t a whole lot of evidence that being lazy makes you fat, though being fat might make you reluctant to engage in lots of activity.
The Time article still makes a couple of routine mistakes like conflating theories regarding how much people eat and the composition of the food we eat. Composition theories tend to work by assuming the quantity of eating is not a choice variable. That is, it may seem like you can cut calories by avoiding a second helping at dinner but you’ll just be hungrier the next morning. Eventually, the theory goes, everyone gives in to hunger.
They also, understandably, soft pedal criticism of the public health organizations.
Then how did the exercise-to-lose-weight mantra become so ingrained? Public-health officials have been reluctant to downplay exercise because those who are more physically active are, overall, healthier.
Really? Reluctant to downplay? I would go so far as to say they engaged in a campaign of misinformation bordering on outright deception. I think they did this with the absolute best of intentions. I also would be willing to concede that by convincing millions of Americans that the Stairmaster will help them loose weight, they have done a lot to improve cardiovascular health. However, the fact remains that the basic idea that exercise can help you loose weight was endorsed without any evidence to support it.
From the American Heart Association
Top 10 Tips for Starting a Physical Activity Program
The American Heart Association recommends that all adults get at least 30 minutes of physical activity every day, or at least more days than not. If you’re trying to lose weight or maintain weight loss, you should get at least 60 minutes each day
From the American Cancer Society
Maintain a healthy weight throughout life.
- Balance calorie intake with physical activity.
- Avoid excessive weight gain throughout life.
- Achieve and maintain a healthy weight if currently overweight or obese.
“Balance calorie intake with physical activity.” Now it doesn’t actually say that exercise can make you loose weight. It effectively says: maintain caloric balance. Sort of like telling a sick person: maintain homeostasis. Clearly, however, the implication is that exercise will cause you to loose weight.
All in all, however, the best thing that we can take away is more skepticism about obesity theory. We just don’t know for sure why people get fat. We don’t even know if historical fatness is related to the current epidemic.
That is, for most of human history people could have been gaining weight for reason X. This is still the reason some people are gaining weight. However, reason Y has come out of the blue and is the reason lots of people are now gaining weight.
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Wednesday ~ August 12th, 2009 at 9:17 am
Levi
Maybe not laziness per se, but the results from a study looking at BMI and personality are interesting (Brummett, et al. (2006). NEO personality domains and gender predict levels and trends in body mass index over 14 years during midlife. Journal of Research in Personality, 40, 222-36). Conscientiousness is (stastically, but seemingly not clinically) significantly correlated with BMI (which itself is a very rough measure of “fatness”). It is unlikely to be a powerful explanation of the increase in obesity (unless personalities have changed rapidly in the past 50 or so years). All the correlations are quite small but it seems like an interesting angle of research.
Another study relating to the topic:
Chapman, et al. (2009). Can the Influence of Childhood Socioeconomic Status on Men’s and Women’s Adult Body Mass Be Explained by Adult Socioeconomic Status or Personality? Findings From a National Sample. Health Psychology, 28, 419-27 (this link may work from UNC’s campus).
Or just search PsycINFO for BMI and personality.
Wednesday ~ August 12th, 2009 at 1:09 pm
Karl Smith
Nice
Just read Brummett at el and it is definately interesting. The multivariate estimate on conscientiousness is way significant though pretty small.
My main concern would be that this is all self reported. Is it possible that conscientious people have a self image more closely tied to socially positive traits and are thus more likely to self-report lower weights or for that matter higher heights.
Even if we don’t get into outright lying, you have the issue of multiple measurements and choosing the most favorable measurement to report. Most people are not aware that this will result in bias and those more motivated to do it will do it more often.
Wednesday ~ August 12th, 2009 at 3:20 pm
TGGP
The General Social Survey had interviewers rate how overweight respondents were on a subjective scale. I had a quick’n'dirty post on how different factors correlate with it a little while back.
Wednesday ~ August 12th, 2009 at 7:32 pm
Steve
What’s remarkable is that it used to be conventional wisdom that exercise doesn’t help you lose weight.
Gary Taubes has an even better article on the topic than the Time one: http://nymag.com/news/sports/38001/
I’d also highly recommend his book on the topic if it’s something that you even have a slight interest in nutrition. He goes into how we came to believe that exercise will help you lose weight and how there has never been compelling evidence to believe it. It’s fascinating.