The release of The China Study by T. Colin Campbell rocked the world of nutrition (as well as the walls of Whole Foods). Printed by a small publishing company known for other scientific masterpieces such as The Psychology of the Simpsons and You Do Not Talk About Fight Club, Campbell’s book quickly hit the word-of-mouth circuit and skyrocketed towards bestseller status, with sales exceeding half a million copies to date.
The premise is that all animal foods—ranging from Chicken McNuggets to a fillet of wild-caught salmon—are responsible for modern ailments like heart disease and cancer. Such diseases, the book claims, can generally be prevented or even cured by shunning animal products and eating a diet of whole, unprocessed plant foods instead.
Although this startling thesis was hard for some to swallow, the book appeared credible due to its exhaustive references and the author’s laundry list of credentials—including a PhD from Cornell, authorship of over three hundred scientific papers, and decades of direct research experience. Perhaps not surprisingly, The China Study was quickly absorbed into the vegan community as a bible of sorts—the final word on the harmfulness of animal foods, and indisputable proof that a plant-only diet is best for mankind. To the exasperation of meat lovers everywhere (especially those who enjoy arguing for sport), once lively debates with vegans were now extinguished with one simple phrase: Just read The China Study!
But despite the book’s black-and-white declarations about animal products—and its seemingly well-referenced arguments—The China Study is not a work of scientific vigor. As we’ll see in this article, the book’s most widely repeated claims, particularly involving Campbell’s cancer research and the results of the China-Cornell-Oxford Project, are victims of selection bias, cherry picking, and woefully misrepresented data.
Does Animal Protein Cause Cancer?
The seeds of animal-food doubt were first planted early in Campbell’s career, while he was working in the Philippines on a project to help combat malnutrition. A colleague informed him of a startling trend: liver cancer was plaguing affluent Filipinos at a much higher rate than their less-wealthy counterparts—a phenomenon that, despite a slew of other lifestyle differences, Campbell believed was linked to their higher intake of animal protein.1 Bolstering his suspicions, Campbell also learned of a recent study from India showing that a high protein intake spurred liver cancer in rats, while a low protein intake seemed to prevent it.2 Intrigued by this gem of little-known research, Campbell decided to investigate the role of nutrition in cancer growth himself—an endeavor that ended up lasting several decades and producing over one hundred publications (none of which pertained to Fight Club).3
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 Studyto 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:
1. High-quality protein promotes cell growth no matter where it comes from;
2. Protein deficiency thwarts the liver’s ability to detoxify dangerous substances; and
3. With more realistic doses of aflatoxin, protein is actually tremendously protective against cancer, while protein-restricted diets prove harmful.
Did the Real China Study Show That Animal Foods Are Associated With Disease?
The China Study only devotes one chapter to its namesake study, but that doesn’t mean it’s not a doozy. Also known as the China-Cornell- Oxford Project, the China Study was an enormous epidemiological endeavor exploring diet and disease patterns in rural China—a project coined “the Prix of epidemiology” by the New York Times. Spanning sixty-five counties and collecting data on a whopping three hundred sixty-seven variables, it generated over eight thousand statistically significant correlations between nutrition, lifestyle factors and a variety of diseases.15
Although a project of such magnitude inevitably found some contradictory and non-causal links, Campbell asserts in his book that the data generally pointed in one direction: “People who ate the most animal-based foods got the most chronic disease,” and “People who ate the most plant-based foods were the healthiest and tended to avoid chronic disease.”16 Although—as echoes through the hearts of statisticians everywhere— correlation doesn’t equal causation, these associations in conjunction with Campbell’s other research are supposed to make a compelling case for animal foods being legitimately harmful.
But were the results of the China Study really a sparkling endorsement for plant-based eating?
It seems this conclusion is based, in large part, on unreliable blood variables rather than actual foods. In his book, Campbell states that he and his research team “found that one of the strongest predictors of Western diseases was blood cholesterol,”17 and proceeds to treat cholesterol as a proxy for animal food consumption. Throughout this chapter, we learn that the China Study data found associations between cholesterol and many cancers, as well as cholesterol and animal protein intake—implying that animal protein and those same cancers must themselves be intimately linked.
But because blood cholesterol can be affected by a number of non-dietary factors and can even rise or fall as a result of disease, examining the relationship between food itself and health outcomes is likely to be more informative than using cholesterol as an overworked, fickle middleman. But the direct relationship between animal protein and diseases isn’t discussed in The China Study for one monumental reason: that relationship doesn’t exist. An examination of the original China Study data shows virtually no statistically significant correlation between any type of cancer and animal protein intake.18 Only fish protein correlates positively, but probably non-causally, with a small number of cancers: nasopharyngeal cancer, a rare disease that only strikes one out of every seven million people; liver cancer, which shows up in fish-eating regions because aflatoxin proliferates in humid areas near water; and leukemia, which is likely linked to other elements of the industrialized lifestyles associated with coastal regions (and thus fish consumption) in the China Study.19
Ironically, when we look at plant protein— which The China Study argues so vigorously is cancer-protective—we find almost three times as many positive correlations with various cancers as we do with animal protein, including colon cancer, rectal cancer, and esophageal cancer.20 Likewise, for heart disease and stroke, plant protein has a positive correlation while animal protein and fish protein have negative or nearly neutral correlations—meaning the animal-food eaters in rural China, if anything, are getting less cardiovascular disease than their more vegetarian friends.
But matters get even more interesting when we look at some of the peer-reviewed papers generated by the China Study data, most of which are co-authored by Campbell himself. As with the casein research, the China Study findings as described in Campbell’s book are a hop, skip, and eighteen thousand jumps away from what the original research says. Although wheat gets nary a mention in the China Study chapter, Campbell actually found that wheat consumption—in stark contrast to rice—was powerfully associated with higher insulin levels, higher triglycerides, coronary heart disease, stroke and hypertensive heart disease within the China Study data—far more so than any other food.21,22 Likewise, in a paper from 1990, Campbell conceded that “neither plasma total cholesterol nor LDL cholesterol was associated with cardiovascular disease” in the China Study data, and that “geographical differences in cardiovascular disease mortality within China are caused primarily by factors other than dietary or plasma cholesterol”—revealing that not even the beloved cholesterol middleman could live up to its heart-disease-causing accusations. 23
And in the spirit of saving the best for last, another of Campbell’s own papers, published a mere two years before The China Study hit the shelves, states point-blank that—despite Campbell’s claims about the superior health of the near-vegan rural Chinese—“it is the largely vegetarian, inland communities who have the greatest all risk mortalities and morbidities and who have the lowest LDL cholesterols.”24 Maybe the lesson here is the same one we gleaned from Campbell’s rats: it’s pretty tough to get sick when you’re dead!
Despite its increasing popularity (and glowing endorsements by high-profile vegan converts like Bill Clinton), The China Study is, in many ways, more a work of fiction than a nutritional holy grail. The book has spawned a number of myths about the hazards of animal protein and the true results of the China Study itself—myths that easily crumble under a scrutinizing eye, but nonetheless continue trickling into the mainstream and gaining mounting publicity.
If there’s anything positive to take away from the book’s four hundred seventeen pages, it’s the promotion of a whole-food diet—and the resulting elimination of vegetable oils, high fructose corn syrup, refined grains, and other industrial products that tend to displace real food on our modern menus. But for those seeking scientific literature of a higher caliber, The Psychology of the Simpsons is likely to be a more satisfying (and animal-product-friendly) read.
- The China Study: Startling Implications for Diet, Weight Loss, and Long-Term Health
- What “The China Study” Gets Wrong About Vegan Diets (Prefer to listen to an audio version of this article? Click the play button below):