Because of its prevalence, the belief that casein causes cancer must have some basis in fact right? Actually, that depends.
The China Study, as written by T. Colin Campbell and his son, was published in 2005 and can likely be considered the most prominent source for this belief.
Let’s dissect the flawed research that supported this correlation to see where and why it went wrong.
After the details are ironed out, I’m hoping that you will all feel much better about reaching for the gallon of milk or for a casein protein shake before bed.
Animal studies and the casein-cancer association:
The rat studies that supposedly back up the casein-cancer link involved giving rats an extremely (toxically) high dose of the tumor-causing agent aflatoxin.
Each group was given a grain and fat diet that included either 5% or 20% casein protein. Tumor growth was significantly higher in the 20% casein group (likely the result that drove the casein-cancer myth).
The thought is terrifying, right? Providing fuel (protein) for tumors doesn’t sound like a good option. However, the outcome of the other, lower-protein group warrants consideration before we draw any final conclusions.
They, uh, became “unalive” too quickly. Due to the rats’ livers inability to keep up with its detox duties, the rats with extremely high exposure to aflatoxin and low protein levels died so suddenly, they didn’t have time for the development of tumors.
Earlier studies that sparked Campbell’s interest in casein and cancer correlations found the same thing: the low-protein group had a much higher mortality rate than the high-protein group.
The problem with this result is that when you’re already dead, it’s hard for your tumor to get any bigger. Thankfully, the casein and aflatoxin experiment was redone on monkeys a decade or so later, with a lower dose of the toxin.
This dose would lead to tumor development but would probably not be lethal to the animals.
Having two groups of animals with similar survival rates throughout the experiments made it possible to compare tumor growth rates.
The monkeys groups had the same casein percentages as Campbell’s rats (5% or 20%). This time, tumors developed in the low-protein group but not in the high-protein group. This result emphasizes the importance of carefully planned scientific experiments.
Researchers in the rat studies used extremely high doses of the agent known to cause tumors, guaranteeing that all of the animals would experience tumor growth and tissue damage.
In that case, tumor size was reduced due to a lack of protein, but animals still died from their injuries.
Because protein promotes cell growth and because there was sufficient tumor-causing agent present to ensure that both healthy and cancerous cells multiplied, the protein-rich animals not only survived but also developed larger tumors.
The animals that were fed a high-protein diet survived longer and were actually protected from cancer when exposed to more realistic levels of the toxin.
Interestingly, when Campbell repeated the casein study but substituted the casein protein for wheat protein with added lysine (to create a complete amino acid profile), he still found that the higher protein group had larger tumors and the lower protein group had more deaths. Even more interesting is that he didn’t include this research in his book.
However, the more accurate conclusions drawn from these studies—that complete protein supports cell growth and high doses of aflatoxin kill—are not even supported by the research he does cites and include.
Studies on humans and the exaggerated health risks of meat:
Campbell’s more broad claims about animal protein and health rest on a single, massive study in China, and that study has some serious flaws.
The first most significant issue is that, although his conclusion is about animal protein consumption and cancer, no direct correlation between these two was actually found from the massive data set of the study which spanned across 65 countries and nearly 7,000 human subjects.
It should be noted that fish consumption was found to be associated with a statistically significant increase in risk for certain cancers. However, it is also possible that this increase is due to other enviormental factors affecting the people who live in areas that consume more fish.
Furthermore, the number of positive associations found between plant proteins and cancer in the original data was nearly three times higher than that of animal protein.
However, since a thorough evaluation of other relevant variables was not carried out, we should also be cautious about jumping to the conclusio that plant proteins cause cancer.
Campbell also conveniently failed to mention these connections between plant proteins and cancer in his book. At best the findings he does articulate appear to have been heavily influenced by confirmatio bias, and at worst is a flagrant case of deliberate data manipulation.
After the failed animal protein-cancer link was discovered, Campbell seems to have sought out alternative methods of evaluation.
Rather than using the ACTUAL food consumption data (which was assessed and also available in the data set that Campbell anlayzed), he instead used blood biomarkers, which he claimed would be elevated in people whose diets included a lot of meat and who convieniently were also the ones with higher rates of cancer. Hence he was able to once again draw a link between meat consumption and cancer.
The problem is that regional differences in diet, as well as differences in sex, different ages, and hormone levels can lead to markedly different biomarkers and associations with specific foods for different people.
When the consumption data was evaluated, the results showed no solid link between eating meat and increased cancer risk.
The Reality of Animal Products
Animal protein aka meat, can also contain a lot of animal fat. Animal fat is typically saturated and, hence, one of the least healthy fats you can eat. In contrast, the majority of plant-based fats are monounsaturated and polyunsaturated, and therefore, much healthier for you.
Some people may object to meat for ethical or animal rights reasons, which is their prerogative, and may even have valid reasoning. However, these reasons should not be confused with the nutritional side of the argument.
Additionally, there are plenty of studies that show that a whole food, plant based diet can also lead to general decrease in all cause mortality. So in conclusion, although eating animal protein does not increase your risk of developing cancer, it does not mean that you necessarily should consume it without moderation.