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.

Leave a Comment

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.

Comments (2)

Should communication between pea plants raise tough issues for vegetarians?

I was just about ready to get back into my review of In Defense of Food this week. That is, until yesterday morning, when Michael Pollan tweeted,

Cool piece on how pea plants communicate with one another, possibly raising some tough issues for vegetarians. p2.to/1jpp

The basic science in the blog post, I have to say, is genuinely interesting. The idea is this:

[A] team of scientists from the Blaustein Institute for Desert Research at Ben-Gurion University in Israel published the results of its peer-reviewed research, revealing that a pea plant subjected to drought conditions communicated its stress to other such plants, with which it shared its soil. In other words, through the roots, it relayed to its neighbors the biochemical message about the onset of drought, prompting them to react as though they, too, were in a similar predicament.

Curiously, having received the signal, plants not directly affected by this particular environmental stress factor were better able to withstand adverse conditions when they actually occurred. This means that the recipients of biochemical communication could draw on their “memories” — information stored at the cellular level — to activate appropriate defenses and adaptive responses when the need arose.

Stuff like this is fascinating to me, and I’d love to know more about it. However, I probably won’t look to the New York Times to further enrich myself because the Times seems to have a rule that requires all discussions of plant responses to external stimuli to include a discussion of the ethics of eating plants and its implications for vegetarians (see also this article from December 2009 and this one from March 2011).

I often hear vegetarians dismiss this argument as a disingenuous display of concern for plants, but I think there’s a bit more to it than that, at least when the argument is made well. Some animal rightists argue that killing animals is incompatible with generally accepted ethical principles. The “right” way to make the “plants like to live” argument is to argue that the very same line of reasoning amounts to an argument against eating plants. If the argument could be made soundly, it would present a problem for the argument against eating animals–unless the person making it were also willing to give up eating plants. The point is that an argument based on a need to be logically consistent doesn’t deserve to be taken seriously if it isn’t itself logically consistent. This an instance of the reductio ad absurdum, which I’ve written about in another context. Such an argument, it should be noted, has nothing to do with whether the person making the argument cares about plants or animals, and everything to do with proving that an argument fails to meet its own standards of consistency.

That said, I believe there are good reasons to give a pig more consideration than a pea plant. More than anything, I see this as an argument that arises from imprecision.

The New York Times piece asks,

Is it morally permissible to submit to total instrumentalization living beings that, though they do not have a central nervous system, are capable of basic learning and communication? Should their swift response to stress leave us coldly indifferent, while animal suffering provokes intense feelings of pity and compassion?

I find myself unmoved by this argument because my “intense feelings of pity and compassion” for animals do not arise from the simple fact of the animals’ capacity for “basic learning and communication” nor from their “swift response to stress.” Such an argument would be even more foolish than the New York Times‘s Michael Marder implies. Indeed one could easily envision computers or robots that had similar traits, but most people’s reasons for not eating these entities are entirely selfish. They probably don’t taste very good, they contain toxic substances, they’re hard to chew, they’re likely to scratch our throats and mouths, and they tend to be a lot more expensive than most foods. I doubt any vegetarian would argue that a computer deserves better than to be eaten.

More broadly, I would reject the idea that the existence of plant survival mechanisms is evidence that plants take an interest in living. Indeed, if one considers the process of natural selection, it shouldn’t be surprising that an organism that’s alive today has mechanisms that have increased its chance of survival. According to the theory of natural selection, those organisms with survival mechanisms should be more likely to have survived. That’s exactly how natural selection works.

The question, then, is what makes animals different? I would argue that the difference lies in the fact that animals tend to respond to stimuli in ways that we can relate to. When we watch a video of a pig writhing at slaughter, it’s easy to believe that we’d react similarly if we were exposed to similar stimuli. Because we associate both the stimulus and the reaction with pain, it’s not unreasonable to guess that the pig is experiencing something similar to what what we know as pain. But that’s not quite enough to draw that conclusion; one could envision a robot programmed to react similarly. The most important piece of information is that science tells us that the pig–unlike a robot–has the capacity to experience pain and suffering similarly to humans. The pig’s suffering is similar in all of those ways to an experience that we want to avoid, but it’s much harder to relate to the pea plant in dry soil. In that respect, I think it’s perfectly reasonable to give the pig more consideration than the pea.

I want to emphasize here that I’m not arguing that an organism should be considered based simply on its overall similarity to humans. Instead, I argue for consideration based on sentience and the interests that arise from it but that sentience can only be meaningfully understood by comparing certain traits (for example, nervous systems and responses to stimuli) to their human counterparts. This means that some traits (e.g. intelligence) are not directly relevant. (If anybody wants to propose an alternative, I’m interested to hear about it in the comments.)

Might this line of reasoning lead to a stronger argument for sparing a pig than, say, a chicken? Perhaps, but the issue is complicated by the fact that it takes many chickens to provide the same amount of meat as a single pig. In any case, I think there’s a good case for giving either more consideration than a pea plant. I’d feel less comfortable saying the same of an ant or an oyster, and that doesn’t particularly bother me.

Inevitably, some will say that this line of reasoning is anthropocentric. Perhaps so, but I don’t see that as much of a criticism at all. Specifically, insofar as it gives precedence to sensations similar to those that we know as humans, I don’t think it’s any more anthropocentric than making decisions based on what we know (and can know) as people. And I much prefer that to the alternative.

Comments (20)

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.

Comments (2)

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.

Comments (3)

Michael Pollan and John Harvey Kellogg

March 30, 2012 at 8:40 am · Filed under In Defense of Food ·Tagged , ,

Michael Pollan argues in In Defense of Food that Americans’ susceptibility to food fads is nothing new. To make his case, he tells of Dr. John Harvey Kellogg and Horace Fletcher. Dr. Kellogg ran the Battle Creek sanitarium, where, Pollan explains,

[P]atients (who included John D. Rockefeller and Theodore Roosevelt) paid a small fortune to be subjected to such “scientific” practices as hourly yogurt enemas (to undo the damage that protein supposedly wreaked on the colon); electrical stimulation and “massive vibration” of the abdomen; diets consisting of nothing but grapes (ten to fourteen pounds of them a day); and at every meal, “Fletcherizing,” the practice of chewing each bite of food approximately one hundred times…Horace Fletcher (aka “the great masticator”) had no scientific credentials whatsoever, but the example of his own extraordinary fitness…was all the proof his adherents needed.

While I think it’s important to distinguish between sound science and food fads dressed up with scientific words, nothing I could say on this topic could compare to the ideas in a comment posted on the local news site Berkeleyside last summer by commenter Bruce Love. With a few spelling corrections, here is Bruce Love’s comment:

Are Pollan and Kellogg all that different? It’s a question that Pollan invites by criticizing Kellogg.

Kellogg, in some sense, got famous and influential by assuring rich people that: Affluent people were smart and superior to others to spend more money on diet issues than most could afford to spend. Kellogg was happy to get a taste of that spending. He assured the affluent that the typical food most affordable to and consumed by hoi polloi was morally inferior when chosen by anyone who might be able to sacrifice to avoid it. He offered that pursuing these newly coined food values for a hedonistic outcome of bodily pleasure was a political and religious virtue. He allowed that a masochistic element to his program of eating and other regimens was proof of its moral superiority. And finally he held that by pursuing these dietary values, one was actually bringing about a transformative improvement to society and the world at large.

So for Kellogg’s followers, you had a dash of self-flagellation, a sense of moral superiority, a valorization of conspicuous consumption, a messianic narrative, a false elitism, a false identification of one’s bodily sense of well-being with one’s political virtue….

Whereas, from that perspective, with Pollan…you have exactly the same thing with fresh curtains. Instead of Kellogg’s god in the equation you have a faith-based interpretation of traditional culture. Instead of a narrative in which science enables the perfecting of diet, you have a narrative in which science currently proves mainly its own limitations in diet design. Instead of services sold at the Sanitarium, you have farmer’s food boutiques, lifestyle small farming for an affluent customer base, and books and lectures.

I’ve very little doubt but that Pollan’s eating advice and notes on the supply chains are vastly better than anything Kellogg had to offer. I’ve very little doubt that many of his fans have had their lives objectively improved by their exposure to Pollan. Maybe his program even does some kind of good in the world — I hope so but I have my doubts. Nevertheless, the negative reactions are easy to understand when you see that the most visible evidence of his reception by the general public more closely resembles a slight update to Kellogg than it signals the dismissal of the social dynamic that gave Kellogg such influence.

I’m not sure I agree that Pollan would admit any “masochistic element” to his dietary philosophy or that Kellogg’s program could reasonably be described as “hedonistic.” However, I do think that the point about the reception of the two dietary philosophies is insightful. While I have known many of Pollan’s fans who were sincere in their concern for the environmental and health issues of which Pollan writes, there have also been those who seemed most interested in the conspicuousness of their consumption. With this in mind, it seems fair to discuss the possibility that Pollan is another of the food faddists whom he decries.

Comments (1)

Dietary advice, nutritionism, and marketing

March 25, 2012 at 9:52 pm · Filed under In Defense of Food ·Tagged , , , , ,

Michael Pollan discusses Americans’ dietary changes in the aftermath of the publication of the Dietary Goals for the United States:

For while it is true that Americans post-1977 did shift the balance in their diets from fats to carbs so that fat as a percentage of total calories in the diet declined (from 42 percent in 1977 to 34 percent in 1995), we never did in fact cut down on our total consumption of fat; we just ate more of other things…Basically what we did was heap a bunch more carbs onto our plate, obscuring but by no means replacing the expanding chunk of (now skinless white) animal protein sitting there in the middle.

How did that happen? I would submit that the ideology of nutritionism deserves as much of the blame as the carbohydrates themselves do–that and human nature. By framing dietary advice in terms of good and bad nutrients, and by burying the recommendation that we should eat less of any particular actual food, it was easy for the take-home message of the 1977 and 1982 dietary guidelines to be simplified as follows: Eat more low-fat foods. And that is precisely what we did. We’re always happy to receive a dispensation to eat more of something (with the possible exception of oat bran), and one of the things nutritionism reliably gives us is some such dispensation: low-fat cookies then, low-carb beer now. It’s hard to imagine the low-fat/high-carb craze taking off as it did or our collective health deteriorating to the extent that it has if McGovern’s original food-based recommendation had stood: Eat less meat and fewer dairy products. For how do you get from that stark counsel of the idea that another carton of Snackwell’s is just what the doctor ordered? (50-51)

I’m not convinced that Americans tried particularly hard to follow the low-fat dietary advice. After all, Pollan chronicled in The Omnivore’s Dilemma the rise of fast food over roughly the same period, even claiming that there’s no animal flesh in nature with as much fat as a chicken nugget.

My main point in writing, however, is to call into question Pollan’s argument that the focus on nutrients made it particularly easy for us to take dietary advice the wrong way. If McGovern’s original advice, to eat less meat and fewer dairy products, had stood, it could have been simplified to “Eat more dairy-free and meatless foods.” Nabisco could have given us dairy-free Snackwell’s (no doubt loaded with hydrogenated vegetable oils), and fast-food chains might have given us breaded vegetable protein instead of chicken nuggets. Thus, the idea that a focus on nutrients makes dietary advice particularly prone to co-optation by food companies is not nearly as obvious as Pollan would have us believe.

Leave a Comment

« Newer Posts · Older Posts »
Follow

Get every new post delivered to your Inbox.

Join 107 other followers

%d bloggers like this: