Last Friday, while working on my last entry, I came to the realization that two sentences in my piece in the Berkeley Science Review in September were not quite right. These sentences contained a number of claims which were either subtly wrong, misleading, or which simply could have been expressed more clearly.
The sentences in question came in my response to Michael Pollan’s assertion that “the dietary advice enshrined not only in the McGovern ‘Goals’ but also in the National Academy of Sciences report, the dietary guidelines of the American Heart Association and the American Cancer Society and the U.S. food pyramid bears direct responsibility for creating the public health crisis that now confronts us.” I wrote,
However, McGovern’s Goals called for a substantial reduction in refined carbohydrate consumption and an increase in consumption of carbohydrates from fruits, vegetables, and whole grains. Americans collectively disregarded both of those recommendations, as well as a recommended decrease in daily energy intake.
These sentences have since been corrected. Here’s what I think deserves correction or further explanation (all data on historical consumption of foods are from USDA loss-adjusted food availability data):
- George McGovern’s Dietary Goals for the United States didn’t directly call for a reduction in consumption of refined carbohydrates (which includes both refined grains and added sugars). The first edition (published in February 1977) called for a forty-percent reduction in sugar consumption. The second edition (published in December of the same year) called for a forty-percent reduction in consumption of refined and processed sugars. This means that it would have been consistent with the advice to replace added sugars with white flour. However, that isn’t what Americans did; they increased their consumption of both refined grains and added sugars. Consumption of added sugars did decrease somewhat as a percentage of total calories after 1977, but not by the 40% recommended by the Goals.
- The Goals left some ambiguity over whether whole grains should be preferred to refined grains. The document listed among a set of “Changes in Food Selection and Preparation” the recommendation to “[i]ncrease consumption of fruits and vegetables and whole grains.” However, later, under the heading “Guide to increasing complex carbohydrate consumption,” the document noted that “there have been no studies that have found whole wheat flour to be superior nutritionally to white flour when consumed in a normal diet, and surprisingly few studies have even considered the question.”
- The recommendation regarding total calorie consumption was found only in the second edition of the Goals. Moreover, that edition didn’t tell everybody to reduce calorie consumption. Instead, it made the recommendation to those who were overweight, and advised the general population to “decrease energy intake and increase energy expenditure.” Most likely, if this advice had been followed it would have resulted in a decrease in energy consumption per capita. However, if I were writing the piece today, I probably would have said that Americans “ignored a warning to avoid excessive caloric intake.”
- Total consumption of fruits and vegetables actually increased slightly in the years after the publication of the McGovern report. However, the percentage of total calories from fruits and vegetables decreased. The Goals typically called for increases or decreases as a percentage of total calorie intake, so I think it is fair to say that the recommendation on fruits and vegetables was not followed. However, the word choice could have been more clear. Unfortunately, I was not able to find data on consumption of whole grains, but consumption of grains increased substantially. (Pollan claims in In Defense of Food that most of the increase was in the form of refined grains.)
While I should have been far more careful in writing these two sentences, I think that the point I was attempting to make was sound. Namely, considering that substantial parts of the dietary guidelines were not followed, it doesn’t make sense to blame the guidelines for health problems that have resulted. That said, it’s important to get the details right, and I should have been more careful. I’ll try harder to do both of those in the future.