(So before you read, apparently casien may lead to cancer in rats because they lived long enough not to die from acute high aflatoxin doses. Casien apparently prevents tumors at all but extreme exposure carcinogens. Read on)
The China Study relayed Campbell?s findings with powerful simplicity. In a series of experiments, Campbell and his team exposed rats to very high levels of aflatoxin?a carcinogen produced by mold that grows on peanuts and corn?and then fed them a diet containing varying levels of the milk protein casein. In study after study, the rats eating only 5 percent of their total calories as casein remained tumor-free, while the rats eating 20 percent of their calories as casein developed abnormal growths that marked the beginning of liver cancer. As Campbell described, he could control cancer in those rodents ?like flipping a light switch on and off,? simply by altering the amount of casein they consumed.4
Despite these provocative findings, Campbell wasn?t ready to declare all protein a threat to public health and stamp the peanut butter aisle with Mr. Yuk stickers. Animal protein, it turned out, seemed to be uniquely villainous. In several of his experiments, when the aflatoxin-exposed rats were fed wheat protein or soy protein in place of casein, they didn?t develop any cancer?even at the 20 percent level that proved so detrimental with casein.5 It seemed that those plant proteins were not only PETA-approved, but also the least likely to turn rat livers into tumor factories.
These findings led Campbell to his firm and famous conclusion: that all animal protein?but not plant protein?could uniquely promote cancer growth. Out with the steak, in with the tofu! But as several critics have pointed out,6,7 that proclamation required a few somersaults of logic (and maybe some cartwheels of delusion). The effects of casein?particularly isolated casein, separated from other components of dairy that often work synergistically?can?t be generalized to all forms of milk protein, much less all forms of animal protein. An impressive number of studies shows that the other major milk protein, whey, consistently suppresses tumor growth rather than promoting it, likely due to its ability to raise glutathione levels.8,9 Another of Campbell?s own studies suggests that fish protein acts as a cancer-promoter when paired with corn oil, but not when paired with fish oil?highlighting the importance of dietary context (and the neverending terribleness of vegetable oils).10
And the kicker: one of Campbell?s most relevant experiments?which sadly received no mention in The China Study?showed that when wheat gluten is supplemented with lysine to make a complete protein, it behaves exactly like casein to promote tumor growth.11 This means that animal protein doesn?t have some mystical ability to spur cancer by mere virtue of its origin in a sentient creature?just that a full spectrum of amino acids provide the right building blocks for growth, whether it be of malignant cells or healthy ones. And as any vegan who?s been asked ?Where do you get your protein?? for the eight hundredth time will answer, even a plant-only diet supplies complete protein through various mixtures of legumes, grains, nuts, vegetables, and other approved vegan fare. Theoretically, a meal of rice and beans would provide the same so-called cancer-promoting amino acids that animal protein does. Indeed, Campbell?s experiments lose their relevance in the context of a normal, real-world diet opposed to the purified menu of casein, sugar, and corn oil his rats received.
But that?s only the tip of the proteinaceous iceberg. In his September 2010 article, ?The Curious Case of Campbell?s Rats,?12 Chris Masterjohn ventured beyond the well lit pages of The China Study to explore the dark alleys of Campbell?s publications firsthand. And what he found regarding the low-protein rats was a far cry from the sunshine-and-lollipops descriptions we read in the book. Although rats consuming a high-casein diet were indeed developing liver cancer as Campbell described, the ones in the low-casein groups?which were portrayed as downright bright-eyed and shiny-coated in The China Study?were suffering an even worse fate. Campbell?s research actually showed that a low-protein diet increases the acute toxicity of aflatoxin, resulting in cell genocide and premature death. Because protein deficiency prevents the liver from successfully doing its detoxifying duties, less aflatoxin gets converted into cancer-causing metabolites, but the end result is massive (and eventually deadly) tissue damage.
Even the research from India that jump-started Campbell?s interest in the diet-cancer link showed that rats on a low-casein diet were dying with disturbing frequency, while the high-protein rats?tumored as they may have been?were at least staying alive.13 (It?s surprising, then, that The China Study promotes a plant-based diet to prevent cancer, when death is equally effective and requires fewer shopping trips.)
More clues for understanding the casein-cancer research come from another Indian study?this one published in the late 1980s, and examining the effects of protein in aflatoxin-exposed monkeys instead of rats.14 As with Campbell?s experiments, the monkeys were fed diets containing either 5 percent or 20 percent casein, but with one important difference: instead of being slammed with an astronomically (and unrealistically) high dose of aflatoxin, the monkeys were exposed to lower, daily doses?mimicking a real-world situation where aflatoxin is consumed frequently in small amounts from contaminated foods. In a fabulous case of scientific switcheroo, this study showed that it was the low-protein monkeys who got cancer, while the high-protein monkeys rejoiced in their tumorlessness.
This apparent paradox highlights a major problem in Campbell?s rat research: the level of aflatoxin exposure plays a critical role in how protein affects cancer growth. When the aflatoxin dose is sky high, animals eating a low-protein diet don?t get cancer because their cells are too busy dying en masse, while animals eating a higher protein diet are still consuming enough dietary building blocks for the growth of cells?whether healthy or cancerous. When the aflatoxin dose is more moderate, animals eating a low-protein diet develop cancer while their higher-protein counterparts remain in mighty fine health.
In a nutshell, the animal protein fear-mongering in The China Study stems from wildly misconstrued science. What Campbell?s rat experiments really showed wasn?t that animal protein is a vengeful macronutrient of doom, but the following:
High-quality protein promotes cell growth no matter where it comes from;
Protein deficiency thwarts the liver?s ability to detoxify dangerous substances; and
With more realistic doses of aflatoxin, protein is actually tremendously protective against cancer, while protein-restricted diets prove harmful.