Health effects and cancer link
Some humans have brought up that casein has been linked to cancer. There are actually two issues being brought up:
- That casein may cause cancer
- That animal protein in general may cause cancer
In both cases, it seems that people's concern can be traced back the book The China Study and three papers, all by T. Colin Campbell.
The China Study
I (Juul (talk)) have not yet read the book. It would be better if we could read the actual research papers that the book seeks to explain, since the book makes several controversial claims and is not itself peer-reviewed. Hopefully the book makes no new claims, since a professor making health claims outside of peer-reviewed literature would be somewhat incriminating. There is a long and fairly thorough critique of the book here. Based on the critique it seems that Campbells conclusions about animal protein are somewhat questionable. It seems that he is repeatedly forgetting to control for important and obvious factors, neglecting to mention other more likely explanations for the data, and ignoring data that doesn't fit his narrative. To be blunt it all in all sounds like a very large and impressive research study that has been used uncritically by Campbell to prop up his pre-existing notions about nutrition. The author of the critique does however find the Casein studies convincing or at least she does not point out any serious flaws.
ToDo Investigate the china studies conclusions about casein.
Casein and cancer
There have been at least three studies linking casein and cancer, all by Campbell, the author of The China Study.
- Dietary protein level and aflatoxin B1-induced preneoplastic hepatic lesions in the rat by Dunalf and Campbell (1987)
- The sustained development of preneoplastic lesions depends on high protein intake by Youngman and Campbell (1992)
- Long-term intake of a low-casein diet is associated with higher relative NK cell cytotoxic activity in F344 rats by Bell, Golemboski, Dietert and Campbell (1994)
We'll discuss these papers separately.
Dunaif 1987
The paper uses aflatoxin injected into the stomach of the rats through a tube. There is mention of 8 control rats that received the same treatment without the aflatoxin, but the important data is missing from the paper. This makes it impossible to tell if there is some compounding effect from the method of delivery of aflatoxin. I find it odd, but not _quite_ suspicious that this data was left out.
I am not well-versed in cancer research, so maybe this aflatoxin method is normal and well-accepted, but it seems to me that if you're using a method like this you should do two studies with different carcinogens to minimize the chance that aflatoxin is acting in unusual concert with casein to cause these effects.
More interesting is the fact that it was not reported what type of casein was used in the study. It may simply be that they fed the rats cow casein and that rats have a serious problem with cow casein. We already know that there can be health problems associated when humans eat certain animal caseins. What about purity and form? Did the casein contain trace amounts of other components of milk like lactose? Was it in its micellar form or was it denatured?
Lastly, the amounts of casein that correlate with heightened levels of cancer are pretty insense. The first heightened levels of cancer appear when the rats receive 6% of their total caloric intace via casein. Let's compare that number to humans. Americans in 2000 ate about 593 pounds of dairy products per year. That's probably less than 10% casein (ToDo calculate this more accurately) so around 271 kg casein per year. Casein contains about 3.56 calories per gram, so the average american receives around 97 kilocalories from casein per year out of 3,770 total kilocalories. That's about 2.6% of total calories from casein. Even if humans have the same reaction as the rats in the study, they would have to get somewhere between 1.5 to 2.3 times the the average amount their calories from casein to have a measurable increase in cancer risk for this specific type of cancer. ToDo find more data on casein consumption to know how many are currently above this level and check if there is any data on a casein cancer link in humans.
Youngman 1992
ToDo
Bell 1994
ToDo
Animal protein and cancer
ToDo