Touch your toes...

If lack of physical activity is really to blame for increased obesity, rather than increased caloric intake, do we switch from soda taxes to mandatory morning callisthenics?

From the American Journal of Medicine's press release on two new studies (here and here):

Sedentary lifestyle and not caloric intake may be to blame for increased obesity in the US, according to a new analysis of data from the National Health and Nutrition Examination Survey (NHANES). A study published in The American Journal of Medicine reveals that in the past 20 years there has been a sharp decrease in physical exercise and an increase in average body mass index (BMI), while caloric intake has remained steady. Investigators theorized that a nationwide drop in leisuretime physical activity, especially among young women, may be responsible for the upward trend in obesity rates.

By analyzing NHANES data from the last 20 years, researchers from Stanford University discovered that the number of US adult women who reported no physical activity jumped from 19.1% in 1994 to 51.7% in 2010. For men, the number increased from 11.4% in 1994 to 43.5% in 2010. During the period, average BMI has increased across the board, with the most dramatic rise found among young women ages 18-39.

I expect to do substantially more walking on moving to Wellington. Optimal policy, if obesity reduction were your goal, would need to consider the relative cost elasticities of caloric consumption and exercise. The jump from about 20% to about 50% of adult women reporting no physical activity does seem pretty large.

Hanley writes as commentary on the Ladabaum et al research:

What is missing from the Ladabaum et al paper is societal context. The finger-wagging Puritan in me wants sedentary folks to get up off the couch and exercise, but my public health background cautions me to go beyond the data tables and look at the lives of Americans today. 

Life, work, and leisure have changed dramatically in the US since 1988. With the blossoming of the Internet; the widespread use of computers and mobile devices at home and at work; and the increasing popularity of video games, our lives have been transformed. On an economic level, the prosperity of the 1990s dissipated after the September 11, 2001 terrorist attacks; years of war; the off-shoring of manufacturing jobs; and the Wall Street crash of 2008. Ubiquitous home foreclosures, lay-offs, and
continued unemployment/underemployment have fueled historic income inequality.

I note that none of the factors listed in her second paragraph really comes into the Ladabaum study, though poverty does correlate with obesity.

She points to poverty among single mothers as potential reason for little exercise (though the study does not give any breakdowns by single/couple household status); I'd wonder if it isn't just practicality. Who's going to get a babysitter to head out to the gym? We're hardly poor, and I couldn't imagine our shelling out for that. And while playing outside with the kids can be rather physically exerting (and is indeed my main form of physical activity), that's most easily done while somebody else is in the kitchen making dinner. In the summer, one of us would fairly regularly take the kids out to the beach or park after work and school while the other got dinner ready. You can't do that as easily in a single-parent household.

Further, while video games have indeed gotten more awesome, television is the main reported leisure-time activity of the poor and low educated. Walking around the block is not expensive; income alone should not be the main constraint except inasmuch as it means longer work hours. I'm reasonably sure, though, that recent data has higher income workers also putting in more total hours than lower income workers. Further, the time-rich unemployed have not been immune. Motivation could perhaps be a bigger issue.

The Australian Monthly [HT: @clairlemon] recently hit on some of the realities of morbid obesity - a very different problem than the smaller expansion in average waistlines.

I ask a young 200-kilo patient what he snacks on. “Nothing,” he says. I look him in the eye. Nothing? He nods. I ask him about his chronic skin infections, his diabetes. He tears up: “I eat hot chips and fried dim sims and drink three bottles of Coke every afternoon. The truth is I’m addicted to eating. I’m addicted.” He punches his thigh.

Addicted. The word is useless in my clinic, a mere barrier to any hope of self-determined change. My patient is not addicted; he’s a very lonely, unemployed young man who has gradually become socially isolated to the extent that the only thing available to him for comfort and entertainment is food. He has no friends, no money to buy other consumables, little education, no partner, no job. Some days he doesn’t leave his bed. The choice for him is to eat this food or experience no pleasure. The surgeon and I discuss his situation, concerned that he may overeat after the band has been fitted. We tell him that surgery may not be appropriate for him, given his situation. The patient is perturbed. “Well, what are you going to do for me if you won’t do the operation? Don’t you have some kind of ethical responsibility to help me lose weight?”

This is where the obesity-as-disease concept leads us – to a situation in which people demand that medicine shoulder the responsibility. What about the responsibility of the individual? And of society? My patient cries because the highlight of his day is returning from the supermarket with a plastic bag full of junk that he will eat and drink in his empty lounge room. What can I do for him? I can threaten him with his early demise, intensify his shame. I can offer him some evidence-based motivational lifestyle interventions – swap Coke for Diet Coke! Prescribe exercise? Walk for an hour at an average pace and you’ll only burn off the equivalent of one slice of bread. I could take the old-fashioned approach and wire his jaw shut. I have no hope of resolving his loneliness, his hopelessness, his lack of a job. I could, and do, refer him to a psychologist – if he’s lucky he may land one who is talented and sensitive and will try to get to the root of why this young man hates his own guts. More likely he’ll be offered a few sessions of behavioural therapy that will make everyone except him feel better.

It does not seem likely, at least to me, that folks like this would change their behaviour all that much in response to a soda tax. Better to try to address problems of long-term unemployment that give rise to this kind of despair.

I'm not offering any policy solutions to obesity. If the health and productivity costs of obesity were terrifically large, employers would start running morning callisthenics programmes to reduce their insurance premiums.* It would be great if cities fixed their regs to allow higher density so more folks could choose to be in more walkable neighbourhoods, but I'd hardly want to force everybody to live in those either.

Further, it may well be that optimal body mass has increased with the increasing opportunity cost of exercise-related leisure activity. It takes some value judgements to say that individuals' observed obesity outcomes are suboptimal where information about the benefits of exercise and about nutrition is readily available. Sure, most folks surveyed will claim that they wish they could be thinner. But whether that's notional or effective demand where half of those surveyed are undertaking no physical activity, well...

In related news, Brand-Miller and Barclay have been cleared of allegations that they'd falsified data in their study showing declining sugar consumption in Australia. Overall sugar consumption is down, though it may be up in some population subgroups. The review notes that increased obesity among those consuming less sugar may come down to reduced exercise.

* Of course, offsetting behaviour can kick in with these things. Follow the link....