Posts Tagged nutrition

In Defense of Food: My Review

Michael Pollan’s In Defense of Food might best be described as a book which fares best when judged by its cover. Below the title, a reader finds some dietary advice which is not a bad place to start: “Eat food. Not too much. Mostly plants.” There are a few good ideas inside the book, too. It would be easy not to look much deeper, as Pollan’s prose is so lively that most readers won’t want to stop and give things a closer look. However, the reader who does bother to check the details sees that In Defense of Food is not a credible work of nonfiction. Pollan twists facts and misrepresents the way science works in the course of assembling exaggerated, false, and contradictory narratives.

Pollan’s central thesis is that introducing science into our food system has done more harm than good and that the best thing for all of us would be to go back to eating a more traditional diet. It’s fair to point out that nutritional science has led to some mistakes (such as recommendations to replace saturated fats with hydrogenated oils), but Pollan devotes too much of his effort to dismantling his own shallow caricature of science. Pollan’s chief criticism of nutritional science is that it adheres to the ideology of nutritionism, which he defines as the belief that foods can be understood by studying their constituent nutrients. He explains that nutritionism is rooted in the idea that foods are “decidedly unscientific things” (19) and that studying individual nutrients is “the only thing [nutritional scientists] can do” (62). He even puts forth the idea that the goal of nutritional science is to find an “X factor” (178) — a single compound that is responsible for good health — so that food processors can add more of it to their products.

But science — to the people who study it — isn’t defined by the consideration of certain “scientific” things with hard-to-pronounce names. The scientific method is a general process for improving our understanding of the world. It entails using observations to form a hypothesis, testing the hypothesis experimentally, and refining that hypothesis based on the results of the experiment. As far as the scientific method is concerned, oranges are as good a subject to study as vitamin C. And nutritional scientists tend to be aware that human nutrition is too complicated to be explained by a single “X factor.” After all, that’s part of what makes their jobs challenging!

As proof of the malignancy of nutritionism, Pollan points to the various sets of nutritional guidelines which encouraged Americans to reduce their fat consumption. As Pollan explains, these recommendations gave rise to products like the SnackWell’s cookie, which was presumed healthy on the basis of its being fat-free. He contrasts the low-fat guidelines with the theory (put forward by Gary Taubes and others) that weight gain results when the consumption of refined carbohydrates promotes fat storage and overeating. If that theory is correct, he explains, “there is no escaping the conclusion that the [official dietary advice] bears direct responsibility for creating the public health crisis that now confronts us” (59-60).

By the end of the book, he’s moved on to blaming that same public health crisis on overconsumption of cheap sweeteners and added fats, pointing out that Americans have added 300 calories to their daily diets since 1980 and citing a group of Harvard economists who “concluded that the widespread availability of cheap convenience foods could explain most of the twelve-pound increase in the weight of the average American since the early 1960s” (186-187). If both the dietary guidelines and the cheap convenience foods are to blame, then it must be that the guidelines encouraged Americans to eat those convenience foods, right?

Not exactly, as it would happen. For all his insistence that Americans have “an unhealthy obsession with healthy eating” (9), Pollan gives us precious little evidence that we’ve actually been following the official dietary advice. Indeed, a reader of the various guidelines would see that falling prey to the food marketers often meant going against the science-based dietary advice. For instance, the second edition of the 1977 Dietary Goals for the United States, one of the main sets of guidelines which Pollan criticizes, included warnings against overeating and recommended a decrease in consumption of both fats and refined sugars. So while the sugary SnackWell’s cookies might have helped to reduce fat intake, the dietary guidelines were hardly an invitation to eat them without restraint.

It should thus be no surprise that in his quest to fault science-based nutritional advice for our public health crisis, Pollan often misleads readers about what the dietary guidelines actually said. He tells us, for instance, that a literature review “found ‘some evidence’ that replacing fats in the diet with carbohydrates (as official dietary advice has urged us to do since the 1970s) will lead to weight gain” (45). It sounds pretty damning, at least until you look at the actual paper, which, in fact, reported “some evidence” that replacing dietary fats with refined carbohydrates leads to weight gain. Pollan, of course, had a very good reason to leave out the extra word: that little bit in parentheses would have been false if he’d included it. The government recommendations never urged Americans to replace dietary fats with refined carbohydrates. Truth be told, the official dietary advice could have done better here, but a reader of the recommendations would see encouragements to decrease our consumption of a major class of refined carbohydrate (sugars) and to eat more unrefined carbohydrates in the form of fruits, vegetables, and whole grains.

But some falsehoods can’t be made to look true just by neatly hiding the pesky details behind a missing adjective, and Pollan’s book contains some of these ideas, too. Indeed, the notion that nutritional scientists study nutrients to the exclusion of foods is incorrect; the ideology of nutritionism that occupies so much of Pollan’s attention is a straw man. A reader might get the sense that something isn’t quite right when Pollan refers to a few nutritional studies that considered whole foods. On the other hand, the reader might suppose, perhaps those studies are outliers. After all, Pollan tells us that (since 1977) the official dietary recommendations have always been expressed in terms of nutrients rather than foods. As an example, he gives us the 1982 report, Diet, Nutrition, and Cancer, in which the National Academy of Sciences “was careful to frame its recommendations nutrient by nutrient rather 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 in terms of nutrients, and two of which were expressed in terms of foods. (Of the remaining three, two were encouragements to keep dangerous substances out of the food supply, and one was a reminder not to drink too much.)

The antidote to nutritionism, as Pollan explains, is “to entertain seriously the proposition that processed foods of any kind are a big part of the problem” (141) and  “escape the Western diet” (142) for a more traditional diet. That’s a bold declaration, considering that “processing” in the food system includes not just things like hydrogenating vegetable oils but also everything from chopping vegetables to slaughtering animals. Pollan reasons that science has made us unhealthy by encouraging us to eat in new ways, but a traditional diet must be healthy because “if it wasn’t a healthy regimen, the diet and the people who followed it wouldn’t still be around” (173). Unfortunately, he thereby misses the rather important point that a diet can be unhealthy without doing away with its eaters. Pollan’s line of argument would, for example, vindicate the diet of white rice that left so many with beriberi. And some day, it may well exonerate the American diet, whose worst health effects tend to show up well beyond reproductive age.

For all that Pollan gets wrong, there is a grain of truth to his message. Though Pollan errs in faulting nutritional science for giving us a license to eat every high-carb, low-fat food that processors might concoct, it is true that it would be a bad idea to assume that a low-fat food is a healthy food. Pollan is probably even right that some people reached that conclusion based on their interpretations of the official dietary advice. However, the lesson to take away from this is not that we should ignore nutritional science but that when we oversimplify our decision-making processes, we leave ourselves particularly vulnerable to cheap marketing ploys. With that in mind, the solution he offers is regrettable. Rather than embracing critical thinking and careful attention to detail, Pollan gives us a few simple rules backed up by the same sort of lazy thinking that he claims to have seen in nutritional science. It should therefore be no surprise that food companies have begun to take advantage of his rules for eating, with Frito-Lay advertising that its Lay’s potato chips have only “three simple ingredients” (less than Pollan’s recommended maximum of five ingredients) and manufacturers reformulating products like Gatorade, Hunt’s ketchup, and Wheat Thins to replace the taboo high-fructose corn syrup with other sugars.

To be fair, a few of Pollan’s rules, such as “eat slowly…in the sense of deliberate and knowledgeable eating promoted by Slow Food” (194) and “plant a garden” (197), will probably prove difficult for food companies to use for their own ends. For the most part, however, these reflect a level of privilege which many people do not have. This isn’t too surprising, as Pollan makes no secret of the fact that he writes for a well-to-do audience when he declares, “Not everyone can afford to eat high-quality food in America, and that is shameful; however, those of us who can, should” (184). That doesn’t invalidate his perspective, but there is nonetheless something a bit distasteful about a bestselling author lamenting the eating habits of people whose lives are worlds away from his own. Absent any indication of a good-faith effort to understand why people might choose to microwave frozen dinners instead of preparing a family meal from home-grown ingredients, Pollan’s work seems less likely to inspire positive social change than, as Julie Guthman puts it, to appeal to “those who already are refined eaters and want to feel ethically good about it.”

Michael Pollan remarks in the introduction of In Defense of Food that had he written the book forty years earlier, it would have been received as “the manifesto of a crackpot” (14). In light of the superficiality of the book’s merits and its loose relationship to the facts, that wouldn’t have been a particularly unfair appraisal. Alas, in the time since the work’s publication in 2008, our collective judgment has proven decidedly less sound. Thanks to its engaging style and appealing commonsense message, In Defense of Food has become required reading for thousands of college students, and its author now stands at the helm of a respected social movement. With the alarming rise in diet-related disease, the time was indeed ripe for someone to fill that leading role. It’s just too bad that it was somebody who mostly gives us the same kind of simplistic solutions and sloppy reasoning that helped to create the problem in the first place.

Also posted at Amazon and Goodreads. For more on In Defense of Food, I recommend the following posts:

You can also look at all of my posts about In Defense of Food.

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The reductionism of nutritional Darwinism

Michael Pollan argues in In Defense of Food that we should ignore nutritional science and stick with traditional diets. He explains,

Confounding factors aside, people who eat according to the rules of a traditional food culture are generally much healthier than people eating a contemporary Western diet…I’m inclined to think any traditional diet will do; if it wasn’t a healthy regimen, the diet and the people who followed it wouldn’t still be around. (173)

This is the dietary philosophy which Daniel Engber called “nutritional Darwinism.” The idea behind the name is that people who eat unhealthy diets will be selected out (in the sense of Darwin’s natural selection) of the human population over time.

On the face of it, it might be an appealing idea, but nutritional Darwinism is reductionist in its own way. Namely, it reduces all of human health to the ability to reproduce and raise offspring who can reproduce. If we only know that a group of people has survived on a particular diet for generations, that doesn’t tell us much about how the people tend to die, how long they tend to live, or any non-fatal health problems they may experience. And as the story of beriberi shows, groups of people have survived for generations on traditional diets that had serious nutritional deficiencies.

However, to fully appreciate the weakness of this line of reasoning, consider what it might say about the “Western diet” from which Pollan urges readers to “escape.” Although Pollan contends that this diet is a relatively recent development, it’s not obvious that it can’t survive for a while. There clearly is no shortage of Americans at reproductive age. Moreover, the “Western diseases”–the conditions such as heart disease and cancer that Pollan blames on the Western diet–tend to strike later in life, so they don’t usually interfere with people’s ability to reproduce. This means that there’s no reason to believe that the Western diet will kill off its eaters any time soon. Therefore, if the principle of nutritional Darwinism is to be believed, the Western diet must be healthy!

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A radical simplification of our diet?

Michael Pollan argues in In Defense of Food that our diets are less diverse than they once were. He explains,

Today [corn, soy, wheat, and rice] account for two thirds of the calories we eat. When you consider that humankind has historically consumed some eighty thousand edible species, and that three thousand of these have been in widespread use, this represents a radical simplification of the human diet. (117)

This is a rather egregious abuse of the numbers. Yes, three thousand species is many more than four species, but these numbers are measuring very different things.

I’ll start with the smallest problem. As Pollan notes, much of the corn and soy is actually fed to animals to produce meats and other animal products for human consumption. Yet for some reason, he doesn’t bother to include the animal species in his count here.

A bigger issue is that when he refers to the number of species that have been historically eaten, he seems to be including species that have been eaten by various cultures across different time periods. This means, for instance, that it includes both the American bison eaten by the Native Americans of the Great Plains and the cassava that has long been a staple in South America. Of course, geographical considerations dictate that it’s highly unlikely that many people have regularly eaten both of these species, so the “eighty thousand edible species” is misleading because it tells us nothing about what any particular group of people have historically eaten.

It’s also deeply misleading to use the four species that provide most of our calories as an indicator of the diversity of our diet. The fact is that some edible species don’t have many calories. If you wanted to get more than a third of your calories from the leafy vegetables that Pollan argues we should be eating more of, you’d better be prepared to wolf down more than three pounds of greens per day. And we could easily add a few dozen species to the list just by visiting the spice aisle of a grocery store, even if there are very few calories to be found there.

So is the American diet unusually homogeneous? I don’t have the time or resources to make that determination, but the evidence certainly isn’t in the data that Pollan cites. However, there is evidence that we are not alone in our dependence on a small number of crops. For example, the United Nations Food and Agriculture Organization estimated that about thirty years ago rice alone contributed 68% of calories to South Asian diets.

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Nutrition science doesn’t claim to have all the answers

In In Defense of Food, Michael Pollan explains what he sees as one of the problems with science-based dietary advice:

When Prout and Liebig nailed down the macronutrients, scientists figured that they now understood the nature of food and what the body needed from it. Then when the vitamins were isolated a few decades later, scientists thought, okay, now we really understand food and what the body needs for its health; and today it’s the polyphenols and carotenoids that seem to have completed the picture.

One has to wonder, if the scientists have long been so confident in the completeness of their understanding of human nutrition, why do they continue researching the subject?

It is true that scientists have sometimes expressed undue confidence in an idea. However, the suggestion that nutrition scientists see human nutrition as a solved problem is patently absurd. These scientists continue doing research precisely because they understand that there are many questions remaing about nutrition.

One 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 be possible, to specify a diet that would protect everyone against all forms of cancer. Nevertheless, the committee believes that it is possible on the basis of current evidence to formulate interim dietary guidelines that are both consistent with good nutritional practices and likely to reduce the risk of cancer.

The authors of the report thus readily acknowledged that they didn’t “really understand food.” They issued guidelines anyway on the belief that useful recommendations could be made based on what they did understand.

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Polyunsaturated fats and heart disease

Michael Pollan concludes his attempted takedown of the lipid hypothesis in In Defense of Food by addressing the supposed role of dietary changes in reducing heart disease:

Even if we accept the epidemic of obesity and diabetes as the unintended consequence of the war against dietary fat–collateral damage, you might say–what about the intended consequence of that campaign: the reduction of heart disease? Here is where the low-fat campaigners have chosen to make their last stand, pointing proudly to the fact that after peaking in the late sixties, deaths from heart disease fell dramatically in America, a 50 percent decline since 1969.  Cholesterol levels have also fallen. Epidemiologist Walter C. Willett of the Harvard School of Public Health…cites the increase in consumption of polyunsaturated fats “as a major factor, if not the most important factor, in the decline in heart disease” observed in the seventies and eighties… And so it would appear to be: We reduced our saturated fat intake, our cholesterol levels fell, and many fewer people dropped dead of heart attacks.

Whether the low-fat campaigners should take the credit for this achievement is doubtful, however. Reducing mortality from heart disease is no the same thing as reducing the incidence of heart disease, and there’s reason to question whether underlying rates of heart disease have greatly changed in the last thirty years, as they should have if changes in diet were so important. A ten-year study of heart disease mortality published in the New England Journal of Medicine in 1998 strongly suggests that most of the decline in deaths from heart disease is due not to changes in lifestyle, such as diet, but to improvements in medical care…For while during the period under analysis, heart attack deaths declined substantially, hospital admissions for heart attack did not. (60-61)

The referenced study is “Trends in the Incidence of Myocardial Infarction and in Mortality Due to Coronary Heart Disease, 1987 to 1994.” As the title suggests, this “ten-year study” is actually an eight-year study. That means that Pollan is attempting to debunk claims made about health trends over the course of a few decades by looking at a much shorter period. Moreover, Walter Willett’s claim applies specifically to the seventies and eighties, but a reader who did not bother to check the references would not realize that the period under consideration by Pollan’s “ten-year study” actually only had three years in common with this interval.

This becomes even more problematic when we look at what people were eating. Specifically, let’s look at the amount of polyunsaturated fats in the US food supply (page 65), which is most directly relevant to Willett’s claim.

Amount of polyunsaturated fat in the US food supply, per capita per day. The red lines indicate the beginning and end of the period considered by the NEJM study.

The data show that consumption of polyunsaturated fats increased from 26 grams per person per day in 1970 to 32 grams per person per day in 1985, with most of the increase coming from 1977 and 1985. However, in 1985 polyunsaturated fat intake more or less leveled out, and the net increase over the period under consideration in the NEJM study was only 1 gram. Thus, even if we were to suppose that Willett were right, it’s not clear that we should have expected to see much of a drop in the incidence of heart disease in the study.

Since dietary changes can have long-term effects on health, this doesn’t necessarily mean that Pollan’s argument is completely wrong. Indeed, the distinction he makes between incidence of heart disease and deaths due to heart disease is an important one. However, it’s just not clear how relevant the study he cites really is. The choice of intervals needs to be justified as a part of his argument, rather than hidden away in the references.

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Mike Gibney critiques “In Defense of Food”

In my dissection of In Defense of Food (which, by the way, hasn’t been forgotten, merely badly neglected for another project that has been eating up my time), I’ve tended to be conservative with my criticism. The reason for this is that I’m not an expert on the subject matter. I’m just some guy with an internet connection 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 particulars of nutrition science are beyond me. So for the most part, I don’t engage in that kind of debate.

However, Dr. Mike Gibney is an experienced nutrition researcher, and he has just posted a criticism of In Defense of Food on his blog. He hits hard, arguing that the book is “peppered with half-truths, circular arguments and highly selective supporting material,” and he has far more authority than I could ever claim. Here’s an excerpt:

Pollen’s belief that health is the driver of food choice in the modern era is a cornerstone of his argument. Take for example the statement he makes: “That eating should be foremost about bodily health is a relatively new, and I think, destructive idea”.  As I pointed out in my blog of April 2nd, the interest in healthy eating is as old as civilisation and this obsession is the pursuit of a relatively minor section of society[1]. The vast majority chooses food that they plan to enjoy and, in making those choices, take care to get some level of balance as regards to their personal health. Every study that has examined the drivers of food choice have come away with the conclusion that the “go – no go” part of food choice is whether the consumer likes the food.  Pollan’s assumption that it is the pursuit of health that drives food choice is an opinion based his personal reflections and observations. However, our own research, published in peer-reviewed journals shows the opposite. In a survey of over 14,000 consumers across the EU, some 71% either ‘agreed strongly’ or ‘agreed’ with the statement: “I do not need to make changes to my diet as my diet is already healthy enough”.  Figure that Mr Pollan!

The putative obsession with food and health of modern consumers that Pollan puts forward arises from the dogmatism and doctrine, which he calls “nutritionism”. He argues that nutrition has reduced the food and health issue to nutrients. In his view, nutritionists see foods solely as purveyors of nutrients and summarises their view thus: “Foods are essentially the sum of their nutrient parts”.  He quotes his fellow food saviour and author Marion Nestle who says of nutrition: “…it takes the nutrient out of the food, the food out of the diet and the diet out of the lifestyle”. Eloquent, but utter baloney! This needs to rebutted along several lines. In 1996, I chaired a joint WHO-FAO committee that issued a report entitled “Preparation and use of food-based dietary guidelines”. The notion behind this was that many developing countries did not have detailed data on the nutrient content of their food supply, that they didn’t have nutritional surveys and that we should encourage the development of healthy eating advice in terms that consumers can understand. Indeed, statistical techniques such as cluster analysis are widely used to study food intake patterns and moreover, there are many examples of systems that score food choice for their nutritional quality. To write a book based on the impression that nutritionist see foods solely in terms of nutrients is simply daft.

I highly recommend reading the whole piece.

Finally, I owe a hat tip to Colby Vorland, who tweeted the piece yesterday.

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Foods are (relatively) easy to isolate

April 5, 2012 at 3:36 am · Filed under In Defense of Food, Science ·Tagged , , ,

Michael Pollan explains the problem with nutritionism:

The problem starts with the nutrient. Most nutritional science involves studying one nutrient at a time, a seemingly unavoidable approach that even nutritionists who do it will tell you is deeply flawed. “The problem with nutrient-by-nutrient nutrition science,” points out Marion Nestle, a New York University nutritionist, “is that it takes the nutrient out of the context of the food, the food out of the context of the diet, and the diet out of the context of the lifestyle.”

If nutrition scientists know this, why do they do it anyway? Because a nutrient bias is built into the way science is done. Scientists study variables they can isolate; if they can’t isolate a variable, they won’t be able to tell whether its presence or absence is meaningful. Yet even the simplest food is a hopelessly complicated thing to analyze, a virtual wilderness of chemical compounds, many of which exist in intricate and dynamic relation to one another, and all of which together are in the process of changing from one state to another. (62)

Of all the things I’ve taken issue with in In Defense of Food, this is probably the one that most consistently makes me cringe each time I read it. The problem is that everything Pollan says about the complexity of foods actually works against his thesis. To claim that a food is “a virtual wilderness of chemical compounds, many of which exist in intricate and dynamic relation to one another” is to say that the chemical compounds in foods are difficult to isolate. Foods, by contrast, are relatively easy to isolate because when scientists study the effects of foods as a whole they take a pass on analyzing that “hopelessly complicated thing.”

Pollan continues,

So if you’re a nutrition scientist you do the only thing you can do, given the tools at your disposal: Break the thing down into its component parts and study those one by one, even if that means ignoring subtle interactions and contexts and the fact that the whole may well be more than, or maybe just different from, the sum of its parts. (62)

In reality, nutrition scientists often do study whole foods and broader dietary patterns, which is why Pollan can claim on the very next page that “researchers have long believe that a diet containing lots of fruits and vegetables confers some protection against cancer.” It’s also wrong to say that nutrients can only be studied one by one; Pollan will later tell us about interactions betwen omega-6 and omega-3 fatty acids.

That said, researchers do expend considerable effort with the nutrient-by-nutrient approach, even if not for the reasons that Pollan cites. Frank Hu and Walter Willett of the Harvard School of Public Health justified this choice in a letter (included in Pollan’s references) responding to T. Colin Campbell’s criticism of reductionism:

Although we agree that overall dietary patters are also important in determining disease risk, we believe that identification of associations with individual nutrients should be the first step because it is the specific compounds or groups of compounds that are fundamentally related to the pathophysiology of the disease. Specific components of diet can be modified, and individuals and the food industry are actively doing so. Understanding the health effects of specific dietary changes, which Campbell refers to as “reductionism,” is therefore an important undertaking.

Not being a dietitian or a public health expert, I’m not going to try to evaluate the merits of this argument. What I think is significant here is that Pollan has invented his own dubious argument for focusing on nutrients instead of discussing an argument that researchers actually use. By doing so, not only does he fail to address the real argument, but he also opens the door to a broader dismissal of scientific inquiry on questions of nutrition.

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