A study in cognitive bias: Poor people spend less on fast food than the middle class (With Bonus Mark Bittman!)

OK, this study has been out for a while, but just today I read some quotes from the senior author of the study in a Time article, and I found them… interesting.

[A] recent study from the University of California, Davis… found that people’s visits to fast-food joints increased along with their incomes, and that poor people were spending fewer dollars on fast food than lower-middle and middle-income Americans.

The authors said their study suggests that the availability of fast food isn’t the only driver of obesity in poor groups. “There is a correlation between obesity and lower income, but it cannot be solely attributed to restaurant choice,” said J. Paul Leigh, professor of public health sciences at U.C. Davis and senior author of the study, in a statement. “Fast-food dining is most popular among the middle class, who are less likely to be obese.”

Not the “only” driver? Can’t be “solely” attributed to restaurant choice? How do they know that it’s a driver of obesity at all among low-income people? Isn’t it also possible that between a lower consumption of fast food, and a weak effect of fast food on obesity rates, that fast food has no significant effect on obesity rates for low-income people?*

The study’s authors agreed that fast food certainly isn’t helping the national waistline. “I’m not a big fan of fast food,” [senior author of the study] Leigh told the Bee. “I’m sure that fast food in general has a big effect on obesity. This research does not contradict that.”

“In general”? Does that mean “for the middle class”? This seems to be just the study author talking about what his gut feelings are. Fast food’s contribution to obesity rates has become one of those “everybody knows” things in our culture (just watch WALL-E to see an example), and Leigh has to live in this culture, too. Anytime you go to a fast food restaurant and see someone with, say, a BMI over 40, that person will stand out, both because of confirmation bias and because they’re unusual-looking–less than 6% of U.S. adults have a BMI over 40. The “I’m sure that” seems to be another way of saying that we don’t have any solid data. If we’re talking gut feelings, my gut feeling is that the increased availability of fast food has some effect on BMIs, but probably not as much as we think.

And this study is evidence of that–but only weak evidence. Middle class people eat less fast food than poor people. Leigh’s conclusion is that fast food “isn’t the only driver” of rates of high BMI for poor people, but it must still have a big effect on high BMI rates in general. Well, it must not have that big an effect, compared to the other “drivers of obesity”, if its effect can be totally wiped out like that!

I was amusing myself with thinking that if they took their usual approach to correlation and causation, the mainstream media could have read this study and reported, “Decreased consumption of fast food linked with higher obesity rates! Better eat more fast food, low-income fat people!” But is there really any doubt that if they had reported the “expected” finding, that poor people ate more fast food, they would be saying, “Yup, fast food obviously causes obesity, what else is new?”** But when the reverse finding is reported, if they were using the same logic, they would say “low consumption of fast food causes obesity!”

There’s another problem with this article. At the beginning of the Time piece, there’s also a statement about how expensive fast food is:

Contrary to popular wisdom, eating at McDonald’s isn’t exactly cheap, costing some $28 for a family of four.

The article hyperlinks the “$28” to a New York Times opinion piece by Mark Bittman. No, the problem isn’t just that it links to a Mark Bittman opinion piece. 🙂 It is that the $28 is based solely on what Mark Bittman thinks a family of four will probably order at McDonald’s. Because Mark Bittman so familiar with the way the typical lower-middle-class family lives.

The “fact” that junk food is cheaper than real food has become a reflexive part of how we explain why so many Americans are overweight, particularly those with lower incomes. I frequently read confident statements like, “when a bag of chips is cheaper than a head of broccoli …” or “it’s more affordable to feed a family of four at McDonald’s than to cook a healthy meal for them at home.”

This is just plain wrong. In fact it isn’t cheaper to eat highly processed food: a typical order for a family of four — for example, two Big Macs, a cheeseburger, six chicken McNuggets, two medium and two small fries, and two medium and two small sodas — costs, at the McDonald’s a hundred steps from where I write, about $28. (Judicious ordering of “Happy Meals” can reduce that to about $23 — and you get a few apple slices in addition to the fries!)

I think that this may be more typical for what a non-budget-conscious family of four would order than what a budget-conscious family of four would order. (The two categories probably imperfectly overlap between “middle-class and richer” and “poor”.) You can get a 2-liter bottle of soda from a grocery or convenience store, go to the drive-thru and get everyone’s meals to go and skip buying the soda at McDonald’s, and you can get a large fries instead of 2 mediums, or a medium instead of 2 smalls. 2 cheeseburgers or a Daily Double are cheaper than 1 Big Mac. The cheap stuff is on the Dollar Menu. The “Value Meals” are actually kind of a ripoff.

Let’s say each person gets half a medium fries (about $2?), 2 cheeseburgers, and 1 of a set of 2 apple pies (all of those things are from the dollar menu, I think). That’s $3.50 per person, $14 total, and I’d say a pretty generous portion of food for each person. If two of the people (kids?) just have one cheeseburger each, that brings it down to $12. The 2-liter of soda would be, what, $2? That would bring you up to $14-16, assuming you drank all the soda in that one meal.

Mark Bittman also says:

In general, despite extensive government subsidies, hyperprocessed food remains more expensive than food cooked at home. You can serve a roasted chicken with vegetables along with a simple salad and milk for about $14***, and feed four or even six people.

What?! Mark Bittman, I’m disappointed in you! Don’t you know that you’re not supposed to base a meal around meat! And Harvard says that milk is bad for you and you should take calcium supplements and/or eat bok choy instead! But hey, the McDonald’s meal isn’t looking so bad after all! To be fair, Bittman goes on to talk about how there are cheaper things to eat than the chicken. Let’s just say that Bittman is basically right, but he can’t resist trying to make the difference in expense seem bigger than it is.

Another argument runs that junk food is cheaper when measured by the calorie, and that this makes fast food essential for the poor because they need cheap calories. But given that half of the people in this country (and a higher percentage of poor people) consume too many calories rather than too few, measuring food’s value by the calorie [does not make sense].

Yeah, why would you eat to satisfy hunger instead of eating an arbitrary volume of food?

Besides, that argument, even if we all needed to gain weight, is not always true. A meal of real food cooked at home can easily contain more calories, most of them of the “healthy” variety.

That’s a bit of comparing apple to oranges… Healthy food cooked at home compared to unhealthy food cooked in a fast food restaurant, rather than healthy vs. unhealthy food cooked at home? Sometimes he’s talking about McDonald’s, sometimes he’s talking about a bag of chips, so it’s not completely clear which he’s talking about. Of course, to the extent that he’s talking about fast food, the study of fast food consumption kind of undermines a lot of the Bittman piece.

On the plus side, Mark Bittman says in this piece that I should make a grilled cheese sandwich****, and so I ate one while I was editing this post. Of course, a lot of Food Police people would say that that’s a “bad” choice and no better than McDonald’s. Mark Bittman, didn’t you check in with the Food Police before you wrote this? Also, I put a slice of ham from the deli in my grilled cheese, and it’s Processed Red Meat, so now I’m going to die! But I also ate some kale, so that cancels it out! No wait, eating bad stuff cancels out the good stuff! Does it depend on which is eaten first? I’m so confused…

*I’m asking this as a question for a reason–I don’t know and I’m not sure if there is enough data for anyone to know. The one truly relevant study I was able to find with a quick search found an increase in obesity rates for children of 5.2 percent when a fast food restaurant was located within a tenth of a mile of a school, but not if it was .25 miles or more away–which seems like an indication that it does have some effect but only a minor one. There was also a study that talked about it in the background section (“Connections Between Fast Food and Obesity”), but it was based on self-reported fast food consumption; self-reported food consumption, at least if it’s in the form of food frequency questionnaires, tend to be highly inaccurate.

**And meanwhile, a bunch of newspaper commenters would be talking about the waste of money of actually scientifically investigating stuff that “everyone knows”–I hope the actual outcome of this study demonstrates why I find these commenters so annoying.
***I have no idea if the price he gives for the chicken meal is accurate, by the way. I just realized that I can say off the top of my head about how much a chicken from the farmer’s market would cost (~$10) but I don’t know how much one from the grocery store would cost… I’m a giant yuppie.

****I mean, pretty much: “Real cultural changes are needed to turn this around. Somehow, no-nonsense cooking and eating — roasting a chicken, making a grilled cheese sandwich, scrambling an egg, tossing a salad — must become popular again, and valued not just by hipsters in Brooklyn or locavores in Berkeley. The smart campaign is not to get McDonald’s to serve better food but to get people to see cooking as a joy rather than a burden, or at least as part of a normal life.”

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3 Responses to A study in cognitive bias: Poor people spend less on fast food than the middle class (With Bonus Mark Bittman!)

  1. Pingback: Fat is not a video game | closetpuritan

  2. Pingback: Correlation is not causation: “obesity epidemic” and animal product consumption | closetpuritan

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