Diet, Nutrition, Cancer, and Sloppy Journalism

Michael Pollan argues in In Defense of Food that the Dietary Goals for the United States, compiled by Senator George McGovern’s Senate Select Committee on Nutrition and Human Needs, ushered in an era in which dietary guidelines focused on nutrients to the exclusion of whole foods. He explains that McGovern’s committee initially recommended a reduction in red meat and dairy consumption before the interested lobbies complained. The result was a compromise, urging Americans to “choose meats, poultry, and fish that will reduce saturated fat intake.”

Pollan explains the significance of the change,

First, notice that the stark message to “eat less” of a particular food–in this case meat–had been deep-sixed; don’t look for it ever again in any official U.S. government dietary pronouncement. (24)

As evidence of this last point, Pollan trots out the National Academy of Sciences’ 1982 report Diet, Nutrition, and Cancer. He tells us,

The lesson of the McGovern fiasco was quickly absorbed by all who would pronounce on the American diet. When a few years later the National Academy of Sciences looked into the question of diet and cancer, it was careful to frame its recommendations nutrient by nutrient rather than food by food, to avoid offending any powerful interests. (25)

He further notes, “With each of its chapters focused on a single nutrient, the final draft of the National Academy of Sciences report, Diet, Nutrition and Cancer framed its recommendations in terms of saturated fats and antioxidants rather than beef and broccoli” (26).

After a few minutes of skimming the report, I couldn’t help but wonder whether Pollan and I had looked at the same document. He is correct to point out that the recommendations referenced fat, rather than meat. He’s not quite correct to say that each chapter focuses on a single nutrient. Some of the chapters discuss multiple nutrients (for instance, Chapter 10, titled “Minerals,” discusses selenium, zinc, iron, copper, iodine, molybdenum, cadmium, arsenic and lead), but on that point he’s close enough for me.

Where Pollan misses the mark badly is in failing to note that the report’s recommendations weren’t found in these nutrient-focused chapters. These chapters summarized the existing science on the various nutrients, without saying what we should do about it. The report did include a section called “Interim Dietary Guidelines,” but this was found in the report’s Executive Summary. Summarized, the guidelines were as follows:

  1. “The Committee recommends that the consumption of both saturated and unsaturated fats be reduced in the average U.S. diet.”
  2. “The committee emphasizes the importance of including fruits, vegetables, and whole grain cereal products in the daily diet…Results of laboratory experiments have supported these findings in tests of individual nutritive and nonnutritive constituents of fruits (especially citrus fruits) and vegetables (especially carotene-rich and cruciferous vegetables).”
  3. “[T]he committee recommends that the consumption of food preserved by salt-curing (including salt-pickling) or smoking be minimized.”
  4. “The committee recommends that efforts continue to be made to minimize contamination of foods with carcinogens from any source. Where such contaminants are unavoidable, permissible levels should continue to be established and food supply monitored to assure that such levels are not exceeded. Furthermore, intentional additives (direct and indirect) should continue to be evaluated for carcinogenic activity before they are approved for use in the food supply.”
  5. “The committee suggests that further efforts be made to identify mutagens in food and to expedite testing for their carcinogenicity. Where feasible and prudent, mutagens should be removed or their concentration minimized when this can be accomplished without jeopardizing the nutritive value of foods or introducing other potentially hazardous substances into the diet.”
  6. “[T]he committee recommends that if alcoholic beverages are consumed, it be done in moderation.”

Thus, of the six interim guidelines, only one was expressed in terms of nutrients, two phrased their recommendations in terms of foods (one of those even recommended eating less of something!), two were seemingly commonsense encouragements to keep dangerous substances out of the food supply, and one was a reminder not to drink too much.

Although the recommendation pertaining to vegetables did briefly mention carotenes, the committee included a clarification between the second and third guidelines:

These recommendations apply only to foods as sources of nutrients–not to dietary supplements of individual nutrients. The vast literature examined in this report focuses on the relationship between the consumption of foods and the incidence of cancer in human populations. In contrast there, is very little information on the effects of various levels of individual nutrients on the risk of cancer in humans. Therefore, the committee is unable to predict the health effects of high and potentially toxic doses of isolated nutrients consumed in the form of supplements.

They were serious about this point, too. In his critique of reductionism (which Pollan quotes), T. Colin Campbell (a co-author of the report) wrote that the Federal Trade Commission sued General Nutrition Centers for using the report’s guidelines to advertise supplements.

Although Pollan has argued that nutrition science “knows much less than it cares to admit” (14), the report shows that the science admits its limits more than Pollan cares to admit. The lack of recommendations on so many of the nutrients considered is an implicit acknowledgment of the lack of evidence. Reading the chapters focusing on the various nutrients, one sees the point made more explicitly. For instance, the researchers wrote in the conclusion of their section on selenium, “firm conclusions cannot be drawn on the basis of the present limited evidence.”

As for those chapters on nutrients, one finds plenty of references to whole foods there, too. For instance, though Pollan writes, “The language of the final report highlighted the benefits of the antioxidants in vegetables rather than the vegetables themselves” (26), the report’s summary of the epidemiological evidence on vitamin A reads,

A growing accumulation of epidemiological evidence indicates that there is an inverse relationship between the risk of cancer and consumption of foods containing vitamin A (e.g., liver) or its precursors (e.g., some carotenoids in dark green and deep yellow vegetables). Most of the data, however, do not show whether the effects are due to carotenoids, to vitamin A itself, or to some other constituents of these foods.

Of course, none of this is directly relevant to the question of how much we can learn about human nutrition by studying nutrients (instead of foods), and it’s on that question that Pollan seems to make his main argument. However, what we can observe here is a pattern of misrepresenting the claims that science has made. This, of course, is helpful to somebody trying to discredit a scientific discipline. But it should be much less helpful if Pollan wants to convince the reader that he is a careful researcher and a credible source of information.

8 Comments »

  1. Timberati said

    Cognitive bias on Pollan’s part appears rather blatant.

    • Adam Merberg said

      Does it? If so, I’m trying to figure out why nobody has documented it in the first four years after the book was published. It might just be that the type of people who read his books want to believe them, and thus have similar cognitive biases.

      • Timberati said

        Pollan appears to want to tell a story more than get the facts, especially not if some of those facts counter his narrative.

        You are not alone. Others have called him on it: Missouri farmer, Blake Hurst; science for Reason magazine, Ronald Bailey; Rob Lyons of Spiked-online; Professor and Willard Sparks Endowed Chair of Agribusiness in the Department of Agricultural Economics at Oklahoma State University, Jayson L. Lusk; Professor of Economics at George Mason University, Tyler Cowen; myself, inter alia.

        Blake Hurst wrote in 2009, “Pollan, who seemed to be aware of the nitrogen problem in his book The Omnivore’s Dilemma, left nuance behind, as well as the laws of chemistry, in his recommendations. The nitrogen problem is this: without nitrogen, we do not have life. Until we learned to produce nitrogen from natural gas early in the last century, the only way to get nitrogen was through nitrogen produced by plants called legumes, or from small amounts of nitrogen that are produced by lightning strikes. The amount of life the earth could support was limited by the amount of nitrogen available for crop production.”
        (The Omnivore’s Delusion: Against the Agri-intellectuals http://american.com/archive/2009/july/the-omnivore2019s-delusion-against-the-agri-intellectuals)

        In 2008, Pollan wrote an open letter to President-elect Obama. Among other things, he said, “[W]hen we eat from the industrial-food system, we are eating oil and spewing greenhouse gases.” He doesn’t appear to be curious in anything beyond the superficial. That local produce needs less fuel to get to market than something that had to be carted halfway around the world appears to be a no-brainer. Had he drilled down, he might have noticed that cargo trucks and railcars carry more than pickups and vans can, so their fuel cost per pound is often less. Therefore, the farm-to-market fuel is a small piece of the farm-to-table energy pie with transportation accounting for only a 14 percent slice on average. Household storage and preparation of food uses more than twice that amount (32 percent). (http://normbenson.com/timberati/2010/11/15/hello-rainforest-it%e2%80%99s-me-organic/)

        As Tyler Cowen notes in his 2006 critique of Pollan’s book, “The problems with Pollan’s ‘self-financed’ [in Omnivor’s final chapter] meal reflect the major shortcoming of the book: He focuses on what is before his eyes but neglects the macro perspective of the economist. He wants to make the costs of various foods transparent, but this is an unattainable ideal, given the interconnectedness of markets.” (http://www.slate.com/articles/arts/books/2006/11/can_you_really_save_the_planet_at_the_dinner_table.single.html)

      • Adam Merberg said

        I was referring specifically to In Defense of Food where I think there’s been less criticism.

        That said, I’m familiar with most of the critiques you mentioned, and I think they tend to miss Pollan’s points. That’s not to say that they don’t have any merits, but that to somebody who hasn’t thought about the issues in depth, it’s likely to sound like just two sides of the same story.

        For instance, Cowen’s piece is interesting and all, but he’s way off to say that Pollan presents “his own model for responsible eating” in the last section (where he gathers everything himself). Pollan made it quite clear that he didn’t see that as how people should eat. So much of his critique will seem irrelevant to people whom Pollan has sold on the idea of buying from their local farmers.

        Hurst’s piece comes closer, in chiding Pollan for misunderstanding nitrogen. But it misses the fact that Pollan claims that his model farm (Polyface Farm) is “completely self-sufficient in nitrogen.” Of course, in the same paragraph where he makes this claim, he also acknowledges that Polyface brings in grain from another farm. As far as I know, he hasn’t been publicly challenged on this contradiction, and most readers aren’t going to pick up on that. They’re just going to nod their heads as Pollan tells them that Polyface is healing the land while providing “the closest thing to the proverbially unattainable free lunch.”

        Maybe I’m overly idealistic, but I think calling him on the factual errors (as I’ve tried to do in this post) would more effectively counter the various false narratives he presents.

  2. […] and access to a good academic library. While I consider myself qualified enough to point out when a document doesn’t say what Michael Pollan claims it does or make general comments on the nature of scientific inquiry, more nuanced points about the […]

  3. […] sees this, for example, in the 1982 report Diet, Nutrition, and Cancer, which Pollan discusses at length. In introducing its interim guidelines, the report explained, It is not now possible, and may never […]

  4. […] to food processors. The report Diet, Nutrition, and Cancer, which Pollan writes about at length (and, I’ve argued, misrepresents), provides a good example of this. Although the report identified some compounds in fruits and […]

  5. […] than food by food, to avoid offending any powerful interests” (25). The only problem is that it isn’t true. The report contains six “Interim Dietary Guidelines,” only one of which was expressed […]

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