In 2006, T. Colin Campbell's "The China Study" emerged, proposing that all animal foods contribute to diseases like heart disease and cancer. Despite Campbell's credentials, including a PhD from Cornell and numerous scientific papers, the book's claims have faced criticism. While embraced by the vegan community, "The China Study" has been scrutinized for its scientific rigor and potential misinterpretations of data.
The Genesis of Animal-Food Doubt
Campbell's early work in the Philippines, aimed at combating malnutrition, laid the foundation for his later conclusions. His research involved exposing rats to high levels of aflatoxin, a carcinogen, and feeding them diets with varying levels of casein, a milk protein. Rats consuming 20% of their calories as casein developed liver cancer, while those consuming only 5% remained tumor-free.
The Casein-Cancer Connection
These findings led Campbell to suggest that animal protein, unlike plant protein, uniquely promotes cancer growth. However, critics argue that generalizing the effects of isolated casein to all forms of animal protein is a logical leap. Furthermore, an experiment omitted from "The China Study" revealed that wheat gluten, when supplemented with lysine to create a complete protein, behaved similarly to casein in promoting tumor growth. This suggests that the amino acid profile of complete proteins, regardless of origin, may influence cell growth, whether malignant or healthy. Complete protein can be supplied through mixtures of legumes, grains, nuts, vegetables, and other vegan fare. Theoretically, a meal of rice and beans would provide the same so-called cancer-promoting amino acids that animal protein does.
The Fate of Low-Protein Rats
Chris Masterjohn's investigation into Campbell's publications revealed that rats on a low-casein diet, portrayed positively in "The China Study," suffered from increased acute toxicity of aflatoxin, leading to cell death and premature death.
Aflatoxin Exposure: A Critical Factor
An Indian study on aflatoxin-exposed monkeys, using lower, daily doses of aflatoxin, showed that the level of aflatoxin exposure influences how protein affects cancer growth. When aflatoxin doses are extremely high, animals on low-protein diets may not develop cancer due to widespread cell death, while those on higher protein diets have enough building blocks for cell growth.
Read also: Is Green Tea the Key to Weight Loss?
The China Study: An Epidemiological Endeavor
"The China Study," also known as the China-Cornell-Oxford Project, was a large-scale epidemiological study exploring diet and disease patterns in rural China. Campbell based his conclusions on unreliable blood variables rather than actual foods. Campbell stated that he and his research team found that one of the strongest predictors of Western diseases was blood cholesterol, and proceeds to treat cholesterol as a proxy for animal food consumption. However, blood cholesterol is affected by non-dietary factors and can rise or fall as a result of disease.
Discrepancies in the China Study Data
The direct relationship between animal protein and diseases isn’t discussed in The China Study for one monumental reason: that relationship doesn’t exist. Peer-reviewed papers from the China Study data, co-authored by Campbell, reveal inconsistencies with the book's claims. While wheat is barely mentioned in "The China Study," Campbell's research indicated that wheat consumption was associated with higher insulin levels, higher triglycerides, coronary heart disease, stroke and hypertensive heart disease. Additionally, a 1990 paper by Campbell conceded that neither plasma total cholesterol nor LDL cholesterol was associated with cardiovascular disease in the China Study data.
Recommendations
Despite its controversial aspects, "The China Study" promotes a whole-food diet, advocating for the elimination of vegetable oils, high fructose corn syrup, refined grains, and other industrial products. Dean Ornish and Caldwell Esselstyn also advocate for limiting sugar, corn syrup, white flour, margarine, vegetable oil, alcohol and any processed food with more than two grams of fat, and forbidding vegetable oils, refined grains, white flour, and products made from enriched flour such as bread, pasta, bagels and baked goods.
The Importance of Sound Methodology
The General Conference Nutrition Council (GCNC) emphasizes the importance of careful and transparent integrity in formulating a sound rationale to support health messages. The design of a study influences the conclusions that can be made from its results. How the data are analyzed is also very important. The China study was what is called an ecological study. An ecological study provides a “snapshot” of the study population at a given point in time. Campbell acknowledges the limitations of such studies. Care must be taken in using ecological or animal data as proof that certain dietary factors cause disease in humans.
Limitations of the China Study
The China study was undertaken at a time of great social turmoil and upheaval in China. Campbell’s team encountered difficulties collecting information and blood samples from the subjects. In addition, the blood samples were transported and stored under less than adequate conditions needed for a major scientific study. An investigation may gather thousands of pieces of data, but it is how those data are used that is important. Campbell states, “… this project eventually produced more than 8,000 statistically significant associations”.
Read also: Heart Health and the Carnivore Diet
Correlation vs. Causation
Campbell rightly notes, “Correlation does not equal causation,” and further, “if someone wants proof that a single factor causes a single outcome, a correlation is not good enough”. It is well-recognized and accepted that when large numbers of tests are performed, there are always some false results. That is, if enough tests are done, it is inevitable that some will appear statistically significant when they really are not. For example, Campbell found no clear association between esophageal cancer and smoking and a negative association with daily alcohol intake. But both smoking and alcohol are known to be important risk factors for esophageal cancer.
Confounding Factors
Based on correlations, researchers may conclude that diet factor X influenced a certain disease Y. However, there might have been another factor Z, that occurred in the diet along with factor X, and it might be that factor Z actually caused the apparent association between X and Y. One way to reduce this confounding is through study design. However, this is not possible in an ecological study like Campbell’s.
The AICR Guidelines
The American Institute for Cancer Research (AICR) has developed evidence-based guidelines to rate the findings of scientific studies. These guidelines recognize that some studies are better designed than others and thus can produce more reliable results. The five categories that classify the strength of associations are given in descending order of strength as Convincing Evidence, Probable Evidence, Limited Evidence, Inconclusive Evidence, No Evidence.
Casein and Cancer: A Reassessment
Campbell's claim that casein is "the most relevant carcinogen ever identified" is contrasted by the AICR guidelines. The evidence supporting his conclusion would be classified as “limited” or “inconclusive”. In addition to all these cautions, research outcomes need to be replicated across gender, age groups, and ethnicities to substantiate the conclusions.
Read also: The Hoxsey Diet