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....

Soda taxes revisited

Soda taxes don't do much to affect obesity. A new paper by Fletcher et al in Health Economics looks at effects of American soda taxes across U.S. states. While 'soda taxes' aren't common, differential sales taxes on soda aren't uncommon; soda is often exempted from generalised food exemptions from state-level sales taxes. Consequently, soda can have an effective tax rate of up to 12% more than other foods and non-alcoholic beverages, though the average was much lower.

They find that sales taxes have no statistically significant relationship to soda calorie intake and may increase consumption of calories from non-soda beverages. In one specification, they find that a one percentage point increase in the soda tax increases total daily caloric intake by 27.7 calories; I rather suspect that they're here picking up an endogeneity problem: governments will implement soda taxes when obesity is rising.

Supporters of soda taxes have suggested that tax hikes in the range experienced in the US will understate the potential effects of a much larger tax hike: if effects are non-linear, this is entirely possible. But Fletcher et al find zero evidence of non-linearities in tax effects within the range of US taxes. If there were some non-linearity, we'd expect there to be at least a little action in the quadratics and high-order polynomials; the linear specification fits best. But we can't rule out non-linearities that only kick in well outside of sample.

They'd previously found strong evidence of substitution effects among children and adolescents: taxes on soft drinks reduced soda consumption but induced an entirely offsetting increase in calories from other non-soda drinks. And recall that Klick et al found that relative prices of healthy and unhealthy foods didn't affect obesity either.

See also Paul Bedard at the Washington Examiner and Chris Snowdon.

Obesogenic environments?

Gareth Morgan wanted restrictions on where "fake food" outlets might be located.

Placement of junk food outlets – local communities have a say over the placement of alcohol outlets, but we can’t stop junk food outlets setting up around our schools or clustering in poor neighbourhoods. This could be changed if planners had to take health into consideration in their decisions.

From The Lancet, online version 29 November 2013:

Influence of the retail food environment around schools on obesity-related outcomes: a systematic review
...
This review of the scientific literature found very little evidence for an effect of the retail food environment surrounding schools on food purchases and consumption patterns, but some evidence of an effect on bodyweight. Given the general lack of evidence for association with the mediating variables of food purchasing and food consumption, and the observational nature of the studies included in this review, it is possible that this finding is a result of residual confounding.

Limit fast food outlets?

Should we blame fast food outlets for obesity?

Canterbury student Alice Robertson thinks so. The University's press release on her internship project has been picked up in a few places (Herald, Press). Alice's paper isn't yet available, but I've been promised a copy when it is. It sounds like it's mainly a literature review; she notes Day and Pearce, 2011 as particularly relevant. That paper found clustering of fast food outlets around schools. Such clustering doesn't prove an obesity link, just that the kinds of places that wind up being decent venues for primary and intermediate schools are also the kinds of places where fast food outlets wind up locating.

Robertson suggests limiting the number of fast food outlets near schools.

Rachel Webb is a doctoral student in our Economics department. She's presenting some of her thesis work at this year's NZAE meetings. She hasn't sought any press releases on her work because she likes making sure everything's nailed down before talking to the press office. And so her paper still says "don't cite without permission". But she's said it's ok for me to post on what she's been up to.

She's investigating links between obesity and high birth weights. In her quest for instruments that might correlate with obesity risk but that should not have any independent effect on high birth weight risk, she thought about fast food venue concentration. There's some evidence that such venue concentration affects obesity. If if doesn't independently affect high birth rate risk, then it can be an instrument (subject to the usual validity tests).

The density of different categories of dining establishments with a particular focus on fast food restaurants within the Territorial Local Authority (TLA) area that the woman resides in comprises my next set of instruments. A significant relationship between fast food restaurant density and obesity has been a prominent finding by health researchers over recent times. Rosenheck’s (2008) systematic review of 16 studies concludes there exists a significant relationship between fast food restaurant density and obesity[21]. It is generally agreed that fast food proximity lowers the notional cost of eating high caloric food and can therefore lead to higher obesity risk though the causality of the relationship is disputed [22]. It should not have any direct effect on high birth weight risk. However, like with rurality, there are plausible factors which could correlate with both food venue type and concentration and high birth weight risk. For instance, if unhealthy food venue options tend to concentrate in areas where people tend to be less health conscious for reasons that transcend deprivation level, ethnicity, age, rurality, or wider region then food venue type and concentration may have an avenue of correlation with high birth weight risk outside of the effect on obesity that I am unable to control for and could invalidate its use as an instrument. It is also possible that food venue type and concentration may be correlated with high birth weight risk through the effect of weight gain during pregnancy. Validity tests are required to check the soundness of this instrument.

So Rachel wasn't interested in the effects of fast food restaurant density on obesity per se: she was just looking for plausible instruments. And she's found something rather interesting.

A curious finding from the first stage results was that the fast food restaurants density in a TLA did not have the expected effect on obesity measures. The majority of the fast food chains showed consistently negative coefficients in the first stage and particular chains such as Hell’s Pizza, Burger Wisconsin, and McDonalds frequently showed a significant negative relationship with the propensity to be overweight, obese, and morbidly obese. KFC and Pizza Hut were the only chains to have a generally consistent positive relationship with obesity risk. It is not clear what is driving these findings as both median income of the TLA and the deprivation level of the meshblock have been controlled for suggesting it is unlikely to be socio-economic status, nor could it be the effect of living in urban areas as rurality variables are also included. The overall number of fast food establishments per person in a TLA was generally insignificant so it doesn’t appear to be driven by substitution away from less healthy options such as fish and chips either. More research into the effect of fast food on obesity is warranted. 

So, fast food restaurant density, in her regressions on New Zealand data, tends to reduce the prevalence of obesity. When she'd first presented this to the Department, I'd wondered whether what she was picking up was that folks hitting McDonald's would otherwise have been going to a fish'n'chip shop and eating even worse food; she's checked that, as noted in the blockquote, and that wasn't driving things.

Rachel wouldn't draw policy conclusions from her thesis work. But I'll draw one: we shouldn't be too hasty to ban fast food outlets near schools. I'll draw a second one: had Rachel sought press releases about her work, there would have been less uptake. There's reasonable media demand for panics about fast food restaurants, and about alcohol, and about "the kids these days".