The Problem of “Food Deserts” is Not (all) About Access

calvin broccoli

From a great big study published by the CDC:

There’s no strong evidence of an association between living within walking distance of places to buy food and being overweight or not, researchers said after interviewing nearly 100,000 Californians. …

“Evidence is more tentative than often presented in the news media and in policy arguments” linking obesity with the food environment, the researchers said.

Here is more, and here is the study itself.  If you look at the statistical tables, they’re pretty striking.  Even where there is statistical significance — which is the exception to the rule — the size of the effect is so tiny, it’s like practically nothing.  For example, on the margin, adding one full-service supermarket within a one-mile radius of your house is associated with an average BMI decrease in your neighborhood of .115.  That is a difference of just one pound.  (see back-of-the-envelope calculations here)

So there is really no relationship, according to this one recent study of nearly 100,000 Californians, between the distance between your body and a full-service supermarket (or any other kind of food store), and whether or not you are obese.  Distance, which is a proxy for access (the idea of a food desert is that the nearest supermarket, which has fresh produce, is distant), is for all practical purposes a non-factor.

Recall what I wrote about food deserts back in December, about the fact that people writing about food deserts make a mistake when they assume that food deserts are all about inadequate supply, instead of inadequate demand.  I suggested that food deserts might exist because people who don’t want to eat healthy will live in neighborhoods without healthy food, not because they choose not to move elsewhere, but because companies that sell healthy food — and this goes for all types of food stores, not just supermarkets — will not make money there.

In other words, lack of demand might cause both obesity and the absence of supply, instead of the usual story about lack of supply causing obesity, with consumer demand completely out of the picture.

But even that story is being too generous, because it appears there is no relationship whatsoever between living in a food desert and being obese — the implication being that even if you’re unlucky enough to live in a neighborhood where nobody wants to buy healthy food, you can still manage to eat healthy.

The same study suggests this hypothesis, via the Department of Common Sense:

A likely reason for the null finding is that shopping patterns are weakly related, if at all, to neighborhoods in the United States because of access to motorized transportation.

Note that “motorized transportation” is not that same thing as “owning a car” — I live in an exurb of Boston, for example, so I take the subway or the bus every day, where I often see people carrying groceries.  They’re not carrying huge amounts of groceries, but they’re enough to feed the family something healthy today, tomorrow, and probably the next day.

What I think is going on in America is that if someone really does want to eat healthy — and they know how to — then they will eat healthy, but huge numbers of Americans “choose” not to.  The cost and the distance don’t much matter.  And I put “choose” in air quotes, because people are not “choosing” per se, rather they are hooked.  They buy sugar instead of broccoli, because sugar tastes awesome and goes with everything, whereas broccoli is gross.  The deck is physiologically stacked in favor of sugar.  The cost and the distance are virtual non-factors for most Americans, outliers notwithstanding, and obesity really does need to be tackled aggressively on the demand side, if at all possible, precisely because distance and cost are virtual non-factors.

The economist’s way of saying the same thing is that unhealthy foods (like sugar) tend to be sort of addictive, or habit-forming, or are at least advantaged by our physiology or biology, so our demand for that food tends to be pretty insensitive to price (or “inelastic”).  And because our demand is insensitive to price, shifting the supply curve one way or the other isn’t going to change the quantity consumed all that much.  You can fiddle with the supply curve all you like, but the problem is ultimately that this inelastic demand curve is keeping quantity consumed stuck more or less in the same place.  So from a public policy and public health standpoint, it’s better to just tackle the demand curve, by shifting it leftward or making it less inelastic, through solid health education curricula or forming good eating habits during childhood, or whatever, if possible.

As for healthy foods, their demand curves work much the same way — they are also inelastic.  Even when healthy alternatives are cheap, we still prefer sugary sweet soda.  Even water is free, yet we still choose sugary, syrupy soda, which is not free.  Hence futzing around with the supply of healthy food, by subsidizing grocery stores (or water, or whatever), really doesn’t make that big of a difference, because again, the problem is that low, inadequate, inelastic demand curve.

For example, when you last ordered food at McDonald’s, did you even notice those ten salads on the menu?  Did you order them?  No, and me neither.  And did you ask for a cup of water, which is free, instead of a soda?  No again.  (That’s my experience anyway, and that of millions of other Americans)

(Keep in mind this is the very simple Econ 101 version of my working hypothesis — I recognize there are all sorts of other complications, and I’m open to competing hypotheses, but you see my point.)

And what’s interesting from a political standpoint, is that this analysis similarly applies to drugs — tackling the supply side does little for heroin addicts, for example, increases the price of heroin, which induces supply to come back into line with the addicts’ inelastic demand curve — and yet most liberals would probably agree with me that drug addiction ought to be tackled on the demand side (spending money to convince young people not to shoot up heroin for example, instead of spending money on patrolling the border), but the same liberals who agree with this analysis of the drug war will often turn around and favor unproven supply-side solutions to obesity like subsidizing supermarkets in low-income neighborhoods, despite the absence of evidence to support those ideas.  Note that libertarians are more consistent on those issues — they oppose supply-side interventions in most, if not all, illicit drug markets, and also oppose supply-side interventions into food markets.

 


PS – Anecdotally, re: the cost of eating healthy, this has been my experience at the super market (I find myself paying more for junk food like Cheese-Its and Ruffles, than for cheaper healthy foods, like salad and chicken), and re: distance to the supermarket, I have on countless occasions opted to eat fast food meals of >100 carbs and >1,000 calories instead of just eating the healthy food that’s already in my kitchen.  I actually leave the groceries at home and eat McDonald’s instead.  I am a little ashamed to admit it, but I even recently drove about 40 minutes away just to eat at a Checkers.

PPS — If there is any place where supply-side interventions in drug and food markets makes sense, it’s in the case of children.  Children, at least up to a certain age, do not even have demand curves (for the most part anyway).  Their quantity supplied of everything is imposed on them by their parents or guardians.  It’s like their whole diet is an externality imposed on them by others.  And since parents don’t have any particular need to eat the same things as their kids (although some may treat their kids as extensions of themselves), those supply curves need not be determined by the parents’ personal food preferences, nor even the child’s.  So for example I might have to drive 45 minutes (just one time, I swear) to Checkers because I’m craving Checkers, but I have no reason not to feed my child that broccoli I left at home — it’s no skin off my back if he eats broccoli, even if he’d prefer fries.


4 comments

  1. Cale
    Cale April 4, 2013 at 4:32 PM |

    Guy thinks Cheese-Its, Ruffles, and McDonalds are actually edible… thinks broccoli is gross… and holds Checkers up as paragon of culinary delight. Guy spends considerable time dissecting a fairly vapid and poorly focused study on diet and obesity. Guy perhaps not seeing the forest for the trees. (And just a hint of confirmation bias?) :)


    1. Jacob A. Geller
      Jacob A. Geller April 4, 2013 at 9:42 PM |

      Yes, guy is fat and has poor taste.

      Guy also had a pre-conceived notion that obesity and distance from supermarkets *would* be correlated, not that they wouldn’t. Guy is disappointed by vapid and poorly focused study that shatters his pre-conceived notion.


    2. ThaomasH
      ThaomasH April 5, 2013 at 5:39 AM |

      The guy is criticizing a study that is weak and not the sort of evidence that would support a cost benefit analysis of subsidizing “food oasises.”


  2. jazzjune
    jazzjune April 11, 2013 at 2:53 PM |

    Food deserts contribute to nutritional deficiencies which lead to disease and illness. It is not only about obesity.


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