Emergent Fitness: Why I have a Problem with Vegetarianism (Part II: The China Study - Cholesterol, Animal vs Plant Based Foods, & Risk of Cancer)

In Part I of this series, I briefly covered one of the more powerful claims made by T. Colin Campbell in his book The China Study; that claim being that all sources of animal protein are carcinogenic. While my analysis was far from comprehensive, I hope I was, at the very least, able to convey the fallacy Campbell makes by categorically subsuming all animal sources of protein under the cancer-causing label by using nothing more than some studies done on casein protein in isolation of other variables. As I stated previously, casein is not representative of all animal sources of protein. Other sources of animal protein, such as whey, have anti-carcinogenic properties.

This discrepancy demonstrates the dangers of using inductive reasoning (reasoning which starts with a particular observation and, thus, is used to infer general laws and theories). Indeed, I think many of Campbell's claims are founded on isolated phenomena (and also hubris and observational bias to a certain extent), and, therefore, lead to untenable general conclusions (general conclusions which are not supported by the majority of scientific research).

Don't misunderstand my negative tone for absolute disdain of Campbell's work. I commend him for his passionate attempt at pointing out many of the flaws which inundate the scientific and Big Pharma industry. Additionally, I think he is absolutely correct in asserting that the SAD (Standard American Diet) foods we're exposed to, in copious amounts, are tearing away at our health as a nation, and in the West in general. Nevertheless, I like to call BS when I see it, and BS there is aplenty in many of Campbell's conclusions.

Over the course of the next several days, I'm going to cover a host of issues with The China Study. I'll be relying heavily upon Denise Minger's critique of Campbell's work, entitled - The China Study: Fact or Fallacy*

*Actually, I'm more or less summarizing her work. Her knowledge regarding this subject is simply too extensive for me to ignore.

Point #1 of Minger's Critique - Unhealthy Levels of Cholesterol Are Causative of Cancer, and Animal Sources of Food Are to Blame? (Nope!)

I think the heading above adequately conveys Campbell's thesis here. He believes that having a serum cholesterol level between 90-170 milligrams/deciliter is positively associated cancer mortality. Moreover, he believes animal protein is causative of this unhealthy cholesterol measurement, and he further believes that plant protein is, inversely, protective against cancer. But, does the evidence support this hypothesis? Minger says no.

Where Campbell's Right

According to Minger, Campbell is right on one account. Animal protein, according to his data, does correlate with higher serum levels of cholesterol. Moreover, unhealthy levels of cholesterol have been associated with higher risk of cancer.

Where Campbell's Wrong

Minger further points out, however that -

when we actually track down the direct correlation between animal protein and cancer, there is no statistically significant positive trend. None.

According to Minger, none of the data Campbell uses shows a direct correlation between animal protein and cancer. In fact, looking at the data, we can see that animal protein was, in actuality, negatively associated with cancer risk in several instances -

Lymphoma: -18

Penis cancer: -16

Rectal cancer: -12

Bladder cancer: -9

Colorectal cancer: -8

Leukemia: -5

Nasopharyngeal: -4

Cervix cancer: -4

Colon cancer: -3

Liver cancer: -3

Oesophageal cancer: +2

Brain cancer: +5

Breast cancer: +12

Note: (-) Negative numbers indicate a negative association, and (+) positive numbers indicate a positive association.

Though you will likely have noted that animal protein does seem to be correlated (correlation does not logically infer causation) with oesophageal cancer, brain cancer, and breast cancer, there are 10 other types of cancer with which animal protein is negatively associated.

But What About Plant Protein?

Another component of Campbell's hypothesis is that plant protein offers protection against most types of cancer. This portion of Campbell's hypothesis arises from looking at his initial claim from another angle -

Cancer associates with cholesterol, cholesterol associates with animal protein, and therefore we infer that animal protein associates with cancer. Or from another angle: Cancer associates with cholesterol, cholesterol negatively associates with plant protein, and therefore we infer plant protein protects against cancer (Minger).

We've already established that the claim incriminating animal protein as causative of cancer is unfounded, but, what of the inverse claim?

Though plant protein does correlate (once again, this does not infer causation) with lower serum levels of cholesterol (according to Campbell's data) -

we also have more positive correlations [between plant protein and cancer] than we saw with animal protein (Minger).

Looking at the data -

Nasopharyngeal cancer: -40**

Brain cancer: -15

Liver cancer: -14

Penis cancer: -4

Lymphoma: -4

Bladder cancer: -3

Breast cancer: +1

Stomach cancer: +10

Rectal cancer: +12

Cervix cancer: +12

Colon cancer: +13

Leukemia: +15

Oesophageal cancer +18

Colorectal cancer: +19

Looking at these numbers, we can clearly see that plant protein is more highly correlated (I've said it already, but here it is again, correlation does not mean causation) with risk of cancer than animal protein.

Wait....What!?

That's right, when we look solely at the correlation between protein source and risk of cancer, we have greater reason to indict plant protein. As Minger states -

when we look solely at the variable “death from all cancers,” the association with plant protein is +12. With animal protein, it’s only +3. So why is Campbell linking animal protein to cancer, yet implying plant protein is protective against it?

Only Campbell can answer Minger's question, so, rather than put words in Campbell's mouth, I'll let the question stand.

Points of Research Campbell Likely Missed

By putting the bulk of his focus on trying to indict animal protein of high crimes against humanity, Campbell may have missed several other factors which more strongly correlate with elevated cholesterol and cancer. Minger points to a number of potential factors, such as: "schistosomiasis infection (correlation of +34*) and hepatitis B infection (correlation of +30*)."

Minger further states -

Not coincidentally, cholesterol’s strongest cancer links are with liver cancer, rectal cancer, colon cancer, and the sum of all colorectal cancers...[S]chistosomiasis and hepatitis B are the two biggest factors in the occurrence of these diseases. So is it higher cholesterol (by way of animal products) that causes these cancers, or is it a misleading association because areas with high cholesterol are riddled with other cancer risk factors? We can’t know for sure, but it does seem odd that Campbell never points out the latter scenario as a possibility.

In Closing

I will readily admit that Minger's claims hardly exuding total certainty. As I discussed in a post entitled "The Truth About 'Proof'", science is, by necessity, a tenuous enterprise. I can't say with total certainty that animal protein is always going to be more or less protective against or causative of cancer in relation to plan protein. I can only speak in probabilistic terms.

Nevertheless, probabilistically speaking, I would like to assert that there is no strong link between animal protein and cancer. Additionally, I believe we would be better served by looking at more strongly associable dietary and lifestyle variables and their correlation with disease risk.

Such is my opinion, but I think it's an opinion worthy of our attention.