Does Every Food Cause Cancer?

This study in the American Journal of Clinical Nutrition reveals the twin problems of: 1) selectivity bias in the academic publication process (papers finding positive results are more publishable than those finding negative results) and 2) epidemiological studies based on cross-sectional data and simple regression analysis (which confuse correlation with causation).

The study picked 50 common ingredients from random recipes in a cookbook and then scoured the published academic research to see if they could find studies purporting a link with cancer.  Here is what they found:

Forty ingredients (80%) had articles reporting on their cancer risk. Of 264 single-study assessments, 191 (72%) concluded that the tested food was associated with an increased (n = 103) or a decreased (n = 88) risk; 75% of the risk estimates had weak (0.05 > P ≥ 0.001) or no statistical (P > 0.05) significance. Statistically significant results were more likely than nonsignificant findings to be published in the study abstract than in only the full text (P< 0.0001).

Here are the authors in the Washington Post:

"I was constantly amazed at how often claims about associations of specific foods with cancer were made, so I wanted to examine systematically the phenomenon,” e-mails study author John Ioannidis ”I suspected that much of this literature must be wrong. What we see is that almost everything is claimed to be associated with cancer, and a large portion of these claims seem to be wrong indeed.”

For reference, here are the ingredients studied:

veal, salt, pepper spice, flour, egg, bread, pork, butter, tomato, lemon, duck, onion, celery, carrot, parsley, mace, sherry, olive, mushroom, tripe, milk, cheese, coffee, bacon, sugar, lobster, potato, beef, lamb, mustard, nuts, wine, peas, corn, cinnamon, cayenne, orange, tea, rum, and raisin

The conclusion isn't that nothing causes cancer.  Rather, one should be careful over-interpreting the results from one or two studies conducted using correlation analysis.  

The Value of Experts

It is often debated whether "experts" should be the ones that decide how to structure our food health, safety, and quality system.  The standard thought is that people are too busy and distracted to properly consider all the relevant evidence and make an informed decision.  As a specialist (dare I say "expert") myself, it is humbling to read pieces like this that show how wrong we often get it.  It is also useful to keep the following in mind when "experts" forecast the impact of some new food or farm policy.

The interview is with Jeremy Howard who works for a website (Kaggle.com) that pays people for correct predictions.  Here are some interesting bits:

and:

PA: That sounds very different from the traditional approach to building predictive models. How have experts reacted?

JH: The messages are uncomfortable for a lot of people. It's controversial because we're telling them: "Your decades of specialist knowledge are not only useless, they're actually unhelpful; your sophisticated techniques are worse than generic methods." It's difficult for people who are used to that old type of science. They spend so much time discussing whether an idea makes sense. They check the visualizations and noodle over it. That is all actively unhelpful.

PA: Is there any role for expert knowledge?

JH: Some kinds of experts are required early on, for when you're trying to work out what problem you're trying to solve. The expertise you need is strategy expertise in answering these questions.

It does make me wonder about the value of theory relative to trial-and-error empirical methods.

Is Wal-Mart Devouring the Food System?

Stacy Mitchell posted a really creative info-graphic over at Huffington post, which I've reproduced below.  

The graphic gets a lot of the statistics right, but draws many wrong inferences.  A few comments:

• The typical concern expressed about Wal-Mart is that they price "too low" and thereby drive all their competition out of business.  I do not doubt that Wal-Mart bankrupts some competitors and creates some adverse consequences for communities (yet the studies cited in this graphic are not a representative selection of the academic research - they convey only the side of the story the author wants to tell).  Moreover, low prices are good for you and I the food consumer.  After all, I've never seen Wal-Mart employees forcing anyone into their stores.  This paper in a 2006 issue of the American Journal of Agricultural Economics, for example, reported: 

Consumers, in contrast, appear to benefit from Wal-Mart's entry in the form of lower prices. Studies focusing on consumer impacts have found that a Supercenter's entry reduces grocery prices. Not only do Supercenters offer lower prices, but their entry may have the indirect effect of lowering prices at competing stores. Estimates of this indirect effect range from 3% overall to as high as 13% for specific items (Basker 2005b; Hausmann and Leibtag 2005).

• The facts reported below could be framed very differently.  Rather than saying Wal-Mart "captures $1 out of every $4" why not say they "earn $1 out of every $4"?
• Yes, production and retailing of food are highly concentrated industries.  The question is why.  Market power is only one possible explanation, and there is theory and evidence that this concentration could relate to economies of scale and cost savings, capacity constraints, and risk reduction, among many factors. And, you can't just look at size, you have to look at how firms behave.  Coke and Pespi are both very big but anyone watching TV ads knows they are in fierce competition.  
• It is a red-herring to cite the farmer's share of the retail dollar as evidence of nefarious processor or retailer behavior.   Processing and retailing costs have risen over time.  Here is a nice paper by Gary Brester and colleagues showing that the farmer's share of the retail dollar is uninformative in this regard and "should not be used for policy purposes."
• It is  untrue that many "farmers are struggling to get a fair price."  Prices for many agricultural commodities are near record highs.  Farm-land values are exploding, in part, due to the extra income on the farm.  For commodities like milk (which is pictured just below the above quote), there are complex government rules that determine the prices farmers get paid.  
• Worker wages may have fallen in real terms, but this is not unique to the food processing industry but is true of real median wages across the entire economy.  People like Tyler Cowen  have argued that this is a result of declines in productivity growth.  So, again, the statistical "fact" is probably right, but the interpretation is misplaced.   

You may still want to visit local farmers markets or local grocers as this graphic exhorts.  But make it an informed decision.   

A New Food Documentery

From the celebrity Chef Tom Colicchio and the producers of Food, Inc comes a new documentary on food entitled A Place at the Table slate for release in March.  I look forward to watching it.  

I see that the subtitle of the new documentary is One Nation Underfed.  I haven't, of course, seen the documentary, but their web site suggests that the film will focus on the problem of hunger.  Ironically, however, here are the folks involved in the movie: 

 sociologist Janet Poppendieck, author Raj Patel and nutrition policy leader Marion Nestle; ordinary citizens like Pastor Bob Wilson and teachers Leslie Nichols and Odessa Cherry; and activists such as Witness to Hunger’s Mariana Chilton, Top Chef’s Tom Colicchio and Oscar®-winning actor Jeff Bridges

Some of these people have been on record in the past talking about how we Americans are Over-fed . And, they've been on record as harshly criticizing precisely those firms and technologies that have made food more convenient and affordable than it once was.  I wish for once the producers of these documentaries would pick (even at random) some of the excellent agricultural scientists working in Land Grant Universities across the U.S. to weigh in on some of these issues.  

I'll withhold final judgement till I watch the movie.  For the time being, however, I will say that I am more sympathetic to the angle that seems to be taken in this food documentary than I was with many of the other's I've seen.  Let's hope this time around the facts are presented in a balanced manner and the suggested alternatives are more well reasoned.  

Stossel on Food

I'm writing this post for two reasons.  The first is to note that John Stossel has been running some interesting pieces on food and he raises a number of interesting points that are often forgotten.

For example, here he is in a piece at Reason.com on impacts of reputation:

Tyson Foods, Perdue and McDonald's have brands to maintain—and customers to lose. Ask Jack in the Box. It lost millions after a food-poisoning scandal. 

Fear of getting a bad reputation makes food producers even more careful than government requires. Since the Eisenhower administration, our stodgy government has paid an army of union inspectors to eyeball chickens in every single processing plant. But bacteria are invisible! 

Fortunately, food producers run much more sophisticated tests on their own. One employs 2,000 more safety inspectors than government requires: "To kill pathogens, beef carcasses are treated with rinses and a 185-degree steam vacuum," an executive told me. She also asked that I not reveal the name of her company—it fears retaliation from regulators. 

The other reason for the post is shameless self promotion.  I filmed a bit yesterday in New York with Stossel on fat taxes, ingredient bans, and the government’s role in food.  The bit is slated to air on a special on Fox News in February.