It is both interesting and gratifying that there has been such a huge response, both on her blog and on those of others. This is a welcome development because it gives this topic an airing that has long been hidden in the halls and annals of science. It is time that this discussion begin to reach a much larger audience, including both supporters and skeptics.
I hope at some point to be able to read all of the discussions and the questions that have been raised, but present deadlines and long-standing commitments have forced me, for now, to focus on the most common concerns and questions, in order to respond in a timely manner here.
the-china-study2.jpgKudos to Ms. Minger for having the interest, and taking the time, to do considerable analysis, and for describing her findings in readily accessible language. And kudos to her for being clear and admitting, right up front, that she is neither a statistician nor an epidemiologist, but an English major with a love for writing and an interest in nutrition. We need more people with this kind of interest.
I am the first to admit that background and academic credentials are certainly not everything, and many interesting discoveries and contributions have been made by "outsiders" or newcomers in various fields. On the other hand, background, time in the field, and especially peer review, all do give one a kind of perspective and insight that is, in my experience, not attainable in any other way. I will try to make clear in my comments below when this is particularly relevant.
My response can be divided into three parts, mostly addressing her argument's lack of proportionality--what's important and what's not.
Misunderstanding our book's objectives and my research findings
Excessive reliance on the use of unadjusted correlations in the China database
Failure to note the broader implications of choosing the right dietary lifestyle
Before proceeding further, however, I would like to make a general comment about my approach in responding to Denise. I believe Denise is a very intelligent person, and I can see how she might reach the conclusions she did; this is easy to do for someone without extensive scientific research experience. Having said this, there are fundamental flaws in her reasoning, and it is these flaws that I will address in this paper. Some might wonder, "Why didn't he go through her laundry list of claims and address each one in the same order?" The answer is simple: these claims are derived from the same faulty reasoning, so it is this underlying problem that I will address. I do in fact illustrate this point by addressing one of her claims regarding wheat, and the reader can assume that one could go through a similar exercise with all her claims.
A. Not understanding the book's objectives.
The findings described in the book are not solely based on the China survey data, even if this survey was the most comprehensive (not the largest) human study of its kind. As explained in the book, I draw my conclusions from several kinds of findings and it is the consistency among these various findings that matter most.
First and foremost, our extensive work on the biochemical fundamentals of the casein effect on experimental cancer in laboratory animals (only partly described in our book) was prominent because these findings led to my suggestion of fundamental principles and concepts that apply to the broader effects of nutrition on cancer development. These principles were so compelling that they should apply to different species, many nutrients, many cancers and an almost unlimited list of health and disease responses (e.g., nutritional control of gene expression, multi-mechanistic causation, reversal of cancer promotion but not reversal of initiation, rapidity of nutritional response, etc.). These principles also collectively and substantially inferred major health benefits of whole plant-based foods.
This earlier laboratory work, extensively published in the very best peer-reviewed journals, preceded the survey in China. These findings established the essence of what can be called biological plausibility, one of the most important pillars establishing the reliability of epidemiological research. [Biological plausibility represents established evidence showing how a cause-effect relationship works at the biological level, one of the principles of epidemiology research established by the epidemiology pioneer, Sir Bradford Hill.]
Unfortunately, this issue of biological plausibility too often escapes the attention of statisticians and epidemiologists, who are more familiar with 'number crunching' than with biological phenomena. The first 15-20 years of our work was not, as some have speculated, an investigation specifically focused on the carcinogenic effects of casein. It was primarily a series of studies intended to understand the basic biology of cancer and the role of nutrition in this disease. The protein effect, of course, was remarkable, and for this reason, it was a very useful tool to give us a novel insight into the workings of the cancer process. [Nonetheless, the casein effect, which was studied in great depth and, if judged by the formal criteria for experimentally determining which chemicals classify as carcinogens, places casein in the category of being the most relevant carcinogen ever identified.]
Second, this survey in rural China, based on a very unique population and experimental format (from several perspectives), resulted in the collection of an exceptionally comprehensive database that, to a considerable extent, permitted the testing of hypotheses and principles learned in the laboratory, both mine and others. By 'testing', I mean questioning whether any evidence existed in the China database to support a protective effect characterized by the nutritional composition of a plant-based diet. I was not sure what might be found but nonetheless became impressed with what was eventually shown.
The China project data afforded an opportunity to consider the collective interplay and effects of many potentially causative factors with many disease outcomes--the very definition of nutrition (my definition of nutrition is not about the isolated effects of individuals nutrients, or even foods for that matter). The China project encouraged us not to rely on independent statistical correlations with little or no consideration of biological plausibility. In the book, I drew my conclusions from six prior models of investigation to illustrate this approach: breast cancer, liver cancer, colon cancer (minimally), energy utilization/body weight control, affluent disease-poverty disease and protein vs. body growth rates. Using this strategy, I first inquired whether a collection of variables in the China survey (ranging from univariate correlations to more sophisticated analyses) could consistently and internally support each of these biologically plausible models and, second, I determined whether the findings for each of these models were consistent with the overarching hypothesis that a whole food, plant-based diet promotes health--I could not discuss much of this rationale in a page-limited book intended for the public.
Most importantly, I cannot emphasize enough that the findings from the China project, standing alone, do not solely determine my final views expressed in the book. That's why only one chapter of 18 was devoted to the China survey project, which is only one link in a chain of experimental approaches. I was simply asking the question whether there were biologically plausible data in the China database to support the findings gained in our laboratory, among others. Because of the uniqueness of the China database, I believed that the evidence was highly supportive. One of the unique characteristics of this survey was the traditional dietary practices of this cohort of people. Mostly, they were already consuming a diet largely comprised of plant-based foods, thus limiting our ability to detect an hypothesized plant-based food effect--thus making our final observations that much more impressive.
Third, in the book, we summarized findings from other research groups for a variety of diseases to determine the consistency of our model with their findings, according to my principles and concepts. One of the most compelling parts of this exercise was the fact that so many of their findings, although published in good peer-reviewed journals, had been and were continuing to be ignored and/or distorted, a very disturbing and puzzling phenomenon. This posed for me the question, why? My participation in extensive reviews of the work of others during my 20-year stint working on or as a member of expert committees gave me a particularly rich opportunity to consider these previously published studies. There still is, and for a long time has been, an intentional effort at various levels of science hierarchy to denigrate studies that speak to the more fundamental biology of plant-based diets. The fact that there has been resistance, oftentimes hostile and personal in the lay community, speaks volumes to me.
Fourth, and most importantly, there is the enormously impressive findings of my physician colleagues, which came to my attention near the end of the China project data collection period and which were showing remarkable health benefits of plant-based nutrition, involving not only disease prevention but also disease treatment (alphabetically: Diehl, Esselstyn, Goldhamer, Klaper, McDougall, Ornish, Shintani-and many others since the book's publication: T. Barnard, N. Barnard, Corso, Fuhrman, Lederman, Montgomery, Popper, Pulde, Schulz, Shewman). I cannot overemphasize the remarkable accomplishments of these primary care physicians. In effect, their work affirmed my earlier laboratory research. I should add that I knew none of them or their work during my career in the laboratory, thus was not motivated or biased to find ways to affirm their work.
It was the combination of these various lines of inquiry that made so compelling the larger story told in the book, at least for me. Denise mostly ignores these fundamental but highly consistent parts of my story. In that vein, I strongly believe that the findings of no single study in biology or even a group of similar studies should be taken too seriously until context is established. Biology is not for engineers and number crunchers, as important as they may be, because, compared to their systems, biological response is much more complex and dynamic.
|