Many believe that animal protein is superior to plant protein. This belief is common but mistaken, and I have written about it many times before. A less common claim that I am also sometimes asked to comment on is this: protein is protein regardless of whether it is from animal or plant origin. My response to this claim is as follows.

The primary difference between animal and plant proteins is their amino acid profiles. It is these amino acid profiles that direct the rates at which absorbed amino acids are used within the body. Animal-based proteins, which are much more similar to our proteins, are used more readily and rapidly by our bodies than plant-based proteins are; that is, amino acids derived from animal-based proteins are more readily available for our protein-synthesizing reactions. Plant proteins, on the other hand, are somewhat compromised by their limitation of one or more amino acid. (Note that when I say compromised, I do not mean plant proteins are dysfunctional or unable to support health; in fact, the opposite is true.)

When we artificially manipulate the amino acid profiles of plant proteins to make them more similar to the amino acid profiles of animal proteins, we produce a response rate equivalent to animal proteins. This supports my earlier statement that the difference between amino acid profiles is the most important factor. My own lab produced experimental data to support this view, and of course, similar observations from other laboratories in years past can also be interpreted this way. To give just one example of how amino acid profiles are important, the ratio of arginine to lysine (two amino acids) is predictive of various tissue responses.

Animal proteins also have a higher concentration of sulfur-containing amino acids, which get metabolized into acid-generating metabolites. As a result, a slightly lower physiological pH must be corrected, and buffers like calcium are used to attenuate these adverse acid effects—to the disadvantage of the host.

But my main thesis, insofar as my own work is concerned, is that our observations on protein and cancer, although useful and studied in considerable detail, were signals of hypotheses that were more important and more global. Thus, I don’t especially like dwelling on the finer structural and functional characteristics of animal versus plant proteins. My views are more in line with this question: what are the consequences—both biologically and socioculturally—of our enormous reverence for protein and especially for “high-quality” animal protein? It is on this path that I find some unusually significant gems.

Much of the critical research pertaining to protein is summarized and referenced in my book The China Study, yet there is more—far, far more. Most of my papers are of a fairly technical nature and oftentimes investigate rather isolated bits of information. One of the main objectives of the book was to integrate and synthesize that information to present a larger picture. What that larger picture suggests is that the outsized emphasis on protein, relative to our focus on other nutrients, has been neither useful nor informative.

Beginning with the discovery of protein in 1839 and continuing until today, we have virtually revered this nutrient. As a result, we have made sure that our more general thoughts about nutrition and health fit into this paradigm. This was especially true when animal-based foods were considered pretty much the only source of protein. In the early years, and still today in many contexts, protein and meat were treated as synonyms. Thus, much of the reverence for protein was really just a thinly veiled reverence for meat.

What I did during the early part of my career was nothing more than what traditional science would suggest: having made the observation that diets presumably higher in animal protein were associated with liver cancer in the Philippines, coupled with my discovery of an extraordinary report from India showing that casein fed to experimental rats at the usual levels of intake dramatically promoted liver cancer, I embarked on an experimental research pathway looking at how this effect worked. We did dozens of experiments to confirm, repeat, and understand these findings. Based on the traditional criteria used to determine carcinogenicity (the ability of a substance to produce cancer) in the government’s chemical carcinogenesis testing program, our research showed that casein should be considered a hugely relevant and powerful carcinogen. This is not a debatable subject, and the implications of this conclusion are staggering in many ways.

However, no matter how important this conclusion may have been in the traditional sense, it did not become the main focus of my subsequent work. It suggested that we should investigate a much broader hypothesis; namely, it demanded a greater focus on the general relationship between animal- and plant-based foods. It also provided evidence that caused me to think of nutrition very differently. I began to think of food-based nutrition as far, far more important in health than nutrient-based nutrition.

In short, our findings on casein and its ability to cause experimental cancer became a stepping stone to much more exciting and relevant questions and conclusions. In the process, many exciting ideas and conclusions arose, two of which are rather profound for me personally. First, it showed me the incredible gap between drug-based health and food-based health (incidentally, I consider nutrient supplements to belong to the first of these categories; these chemicals are often given at a different time from traditional drugs, but they are otherwise the products of a very similar logic). Second, it showed me how wrong we have been in developing and using nutrition as a concept to maintain health and prevent disease. In this, I became a serious cynic about medical practice in general, research investigations in particular, and policy development in the obscene.

I know that some drugs can be life saving when used judiciously. But our dependence on drugs and our addiction to the marketplace and its claims about nutrition supplements, drugs, and other medical paraphernalia is sickening—literally so.

And so, to conclude, I suggest that debates about protein should expand to focus on animal- versus plant-based food more generally. Although the evidence pertaining to the damaging effects of animal protein in particular is very strong and convincing, we can learn much more, and make far more progress, by expanding our scope.

I should also add that the focus on the hazards of saturated fat and cholesterol (in animal food, of course) as the culprit for chronic heart disease came about historically because it was possible to reduce the intake of these components without reducing the intake of the animal food itself. Just take out some of the fat (leaving skim milk, lean cuts of meat, etc.). But the protein cannot be removed; it would no longer even look like animal food. Thus, there has been tremendous pressure over the years not to venture into questioning animal-based protein, for it would mean sacrificing animal foods.