I recently watched a documentary called "Forks over Knives". The premise of this film is that you can avoid a lot of illnesses, especially cancers and heart disease, if you avoid all animal-based foods and eat only non-processed, plant-based foods. Let me state right from the start that I immediately saw this for what it is - vegan propaganda. I found some good blog posts that dissect the film bit-by-bit and point out what is wrong with the arguments and with the science. That's not the point of this post.
What I want to write about today is one particular bit of evidence that the film uses to make its case. They refer to a study done in India that studied the effects of a diet high in casein (milk protein) on the incidence of cancer in rats. They report that rats who received a high-casein diet had higher incidence of cancer than rats on a low-casein diet. From this, the film draws the conclusion that diets high in animal proteins promote cancer growth, and thus all animal products should be avoided.
If you take this as reported, it's pretty scary. In fact, even if you don't accept the leap from casein to all animal proteins, it makes you think you might want to cut down or eliminate dairy foods from your diet. But, I'm skeptical. If this link between milk and cancer had been proven, first, we would see rampant cancer in places like the U.S. where dairy consumption is high. We don't see this. Second, many more studies would have been performed to verify this claim, and it would be all over the news. It's not. So what's the truth?
First, we have to look at what the study really said and what it was trying to find out. Any scientific experiment is designed to answer a question. Scientific experiments are expensive. They are carefully controlled to limit the number of different factors that could influence the outcome. They want to get quality answers to a specific question with the least cost in time and resources. So what was the casein experiment trying to accomplish? They were specifically looking at a carcinogen called aflatoxin and the effect of the level of protein in the diet on aflatoxin's ability to cause liver cancer. Why aflatoxin? Well, aflatoxin is produced by a fungus that can grow on grains in humid climates. I assume that in India, there is a higher risk of being exposed to aflatoxin due to their diet that is high in grains and the tropical weather. Thus, it makes sense that Indians would be studying this toxin. Why study using casein? I don't really know. I'll guess that it's because it's a readily available protein that's available in a pure form that can be used to carefully regulate the protein level in an animal's diet. It's probably just the typical diet protein that biologists use.
So, now that we know what the Indians were studying, let's look at the results. What the movie didn't say was that over half of the low-protein rats actually died before they reached one-year old and were examined for cancer. Low-protein actually means malnourished. The underfed rats didn't have enough protein in their diet for their livers to grow and properly metabolize the aflatoxin. So the alfatoxin destroyed their livers and killed them. The high-protein rats were actually receiving a balanced diet. Their livers grew properly and were able to metabolize the aflatoxin. However, the aflatoxin doses were very high, so they still got cancer, but at least they lived long enough to get a cancer.
This result also gives us insight into what else the Indians may have been trying to study. In a country with rampant malnutrition, they may have been wanting to see if Indian children without sufficient nutrition were more susceptible to aflatoxin damage.
So, let me summarize all this. In India in 1968, researchers performed a series of experiments on rats to see if malnutrition would make it more likely for children to die from exposure to a toxin that is often found in their food supply. The researchers happened to use casein, a readily available protein to carefully control the nutrition level the rats received. Thirty or so years later, a doctor with a strong ideological bias that animal foods are bad for you, took this study and misrepresented the results to say that the experiment showed that high levels of animal-based proteins cause cancer growth.
There are two obvious, but unfortunately common, problems with this. First, the doctor took a study intended to measure one thing and reported only specific aspects of it to make his case, which had little to do with the original study. Second, an experimental study on rats was generalized and reported as if the results were automatically and obviously applicable to humans. Rats aren't people (even if some people are rats). However, mice and rats have enough in common with people biologically and genetically that doing initial studies on rodents can provide information that is useful for later studies with humans.
Vegan propaganda aside, we see this kind of situation all the time. We see headlines like "Eating walnuts cuts breast cancer risk in half". If you look closer at the study, you find that it was a mouse study where half the fat in the mice's diet was replaced by walnuts. Breast cancer incidence was reduced. I don't know the rest of the details of the study, but I can guarantee you that it doesn't show conclusively that you can cut your breast cancer risk in half by eating some walnuts every day.
The media sensationalizes scientific results to make a story. The result is that people don't believe anything that scientists say. "Walnuts prevent cancer? Heck, last week they said that they were bad for you." Never assume that a headline accurately represents the results of a scientific study. It's more likely that the science has made some advancement on one piece of the puzzle that is cancer (or some other disease). The true story is likely much more interesting than the glossy, sensationalized version that the media will give you. The link between malnutrition and the risk of aflatoxin poisoning is much more interesting, useful, and true than "animal-based foods cause cancer".