Organic produce and the causal inference questions which should be asked

Johns Hopkins University took a bold step recently, pledging to use at least 35% local, organic, and sustainable food items by 2020. Hopkins is now one of roughly 20 schools that have made similar commitments, as part of what is called the Real Food Challenge.

The Hopkins move, along with several research articles which have come out over the past couple of years, brings up a few interesting debates, many of which most Americans grapple with on a weekly basis. In this post, I consider a few of the important questions.

First, is it best to buy organic food?

The answer to this one is a pretty strong Yes.

Each year, the Environmental Working Group posts a list of the “Dirty Dozen” fruit, coming with a recommendation that people buy these foods in organic form. Included on these lists have been staples of many American diets, including strawberries, blueberries, and potatoes. Testing in strawberries, for example, turned up nine known carcinogens. If given a choice between organic and non-organic, it seems safe to say that organic foods are safer.

Of course, most people probably knew that already.

We know it’s better to eat organic. So what’s the problem?

One major factor is cost. While a pint of California strawberries costs between $2 and $4 at most local markets, the same sized organic strawberries are substantially more, often twice the cost. As a result, when Americans go to the market, the question they are asking themselves isn’t “Should I buy organic”, it’s more like:

Real Question 1: Is it better to eat two pints of regular strawberries (and their pesticides) or one pint of organic ones? Both cost the same. Or how about one pint apiece of traditional strawberries and blueberries, versus a pint of organic strawberries?  This is often the real decision one makes at the grocery store,

Real Question 2: Are the harmful effects of consuming the pesticides in non-organic produce enough to offset the benefits of fruits and vegetables? If strawberries with pesticides were so unhealthy that we shouldn’t eat them anyways, that would be a game-changer.  I don’t think that’s the case, and that opinion, along with the cost factor, is why I generally don’t buy organic.

Of course, part of the problem with answering these questions is that the answers are not immediate; the effect of pesticides, or of eating healthy, can take years, and might not be feasible to test clinically.  I tried to identify if any research has been done into answer either of the causal questions I posed above, but couldn’t come up with anything.  

What else is going on?

One important assumption in my research in causal inference which certainly applies here can be called that of a “constant treatment assignment,” in which it is assumed that treatment – say, a non-organic pint of strawberries – is the same among all subjects who claimed to have received the treatment. With non-organic produce, however, that’s not the case – washing strawberries, for instance, can remove up to 75% of their pesticides. If two people buy non-organic strawberries, but only one washes those strawberries, it might not be a good idea to group them together.

This factor, among others, is likely why studying the causal effects of eating organic produce is quite difficult.

So what can be done?

For starters, it helps when institutions like Hopkins take the steps – and the possible financial hits – to use organic items. If the US could find ways to make it easier, and cheaper, for Americans to buy organic, that would certainly help. At my local Stop & Shop, for example, organic strawberries are generally hidden behind the traditional, cheaper ones.  If they were side by side, and the same cost, I’d be much more likely to buy the healthier items.

Moreover, the research which has already identified the dangers of eating pesticides could consider identifying answers to the causal inference questions I posted above. Until that happens, I, and probably many other folks, will still be stuck in the same spot of the grocery store, not knowing if buying organic is worth it.


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