Just to be sure that this wasn't another urban legend, I turned to Amazon.com. Well, Jane Plant and her book Your Life in Your Hand (the US edition is entitled The No-Dairy Breast Cancer Prevention Program: How One Scientist's Discovery Helped Her Defeat Her Cancer) checks out. So much the worse for Plant as you'll see. Go read the widely available excerpt from her book (that particular website goes to show how governments are not necessarily keepers of the light, enlightenment that is).
Allow me to put cart before the horse and provide you my conclusion: Geologist and professor Jane Plant is incompetent. I say that because she's supposedly a scientist and yet she commits errors in thinking and analysis that would earn science undergrads a failing grade. How she could, in the same breath, remind us she's a scientist and write as a woowoo is jaw dropping.
Now for my arguments.
Plant tells us that it dawned upon her that in China practically no one drinks cow's milk and that dairy products including cheese are not part of the diet. She also says that statistics show that only 1 in 10,000 women in China die from breast cancer, while the figures for Western countries is around 1 in 10. (Let's at the moment just take for granted that she has her numbers right, although those would need to be checked too of course--I'm suspicious of the 1 in 10 stat). So Plant puts two and two together and comes up with the hypothesis that dairy product consumption might be a or the culprit.
Can we jump to the conclusion that milk is dangerous to women's health? Most certainly not. There's a truism in statistics and science: Correlation does not necessarily imply causation. Correlation is the phenomenon wherein two or more variables/events are associated with one another. For example, the temperature of the ground is correlated with the time of day--the closer it is to noontime the warmer the ground is. And of course this is because the sun heats the earth up. However, just because two variables are correlated does not mean one causes the other. The clock we used in recording the time of day obviously does not cause the ground to heat up. Yet another example. Over two decades ago researchers in Taiwan found that there is a strong correlation between the number of electrical appliances (including toasters) that a household owns and the frequency of use of birth control methods. Does this mean then that buying more appliances causes people to resort to contraceptives more often? Or does it mean that higher frequency of employing contraceptives makes Taiwanese buy more appliances? One of these would have to be our conclusion if correlation were equivalent to causation. The truth of the matter, however, is that the above variables are both correlated with yet other variables, namely, income and educational attainment. And it is these two latter factors that cause the increase in both number of appliances owned and contraceptive use. Income and education are both correlated with the former two variables. They also are causal factors.
In summary, if X is correlated with Y then either X causes Y, or Y causes X, or neither X nor Y is a cause of the other. On the other hand, if Q is the known cause of P, then Q and P will by necessity be correlated with one another. So while correlation does not necessarily imply causation, causation necessarily implies correlation.
In discussing Plant's hypothesis, another friend reminded me of how the Chinese consume a lot of soybean in its various forms--tofu, soybean milk, soy sauce, salted soy beans, etc. That in itself would correlate significantly with breast cancer mortality since Westerners consume less soybeans than Orientals. Just as with dairy products we could also say something like, It might be that the high consumption of soybean products guards against the occurrence of breast cancer. And these surely are not the only variables that correlate with breast cancer incidence and mortality. You could scour the world for various factors and find correlations, both positive and negative.
Plant goes on to tell us that based on this correlation and hypothesis of hers, she stopped taking any product that contained milk. She narrates what happened soon thereafter:
About two weeks after my second chemotherapy session and one week after giving up dairy produce, the lump in my neck started to itch. Then it began to soften and to reduce in size. The line on the graph, which had shown no change, was now pointing downwards as the tumour got smaller and smaller.She goes on to conclude that based on her experience she was right in identifying milk as the cause.
It was difficult for me, as it may be for you, to accept that a substance as ‘natural’ as milk might have such ominous health implications. But I an i living proof that it works....Well, unfortunately for Plant, her reasoning is flawed. She commits the post hoc ergo propter hoc fallacy (after this, therefore, because of this). This is a causal attribution error whereby just because event B comes after A, we conclude that A caused B. Thus, just because the sun rose after the rooster crows obviously does not imply that the chicken made the sun rise. But this is precisely what Plant is saying. She tells us that she stopped taking any dairy product after which she noticed that her lump started waning until it totally disappeared. She then attributes this to her diet change. This is a textbook case of causal attribution error.
But note how she herself tells us that she was simultaneously undergoing chemotherapy, a treatment modality that is known to work against cancer. Why does she not attribute the remission to chemo? So what actually caused her lump to up and disappear? Well, we don't know for sure. It may have been the chemo, the diet change, both of these, spontaneous remission, or something else. To jump to the conclusion that it was diet change is to commit the post hoc fallacy.
Furthermore, Plant has the gall to jump to a conclusion based on her own personal experience. One anecdote is not evidence. And even if a thousand other women shared a similar story, it would still not be evidence. Thus, the aphorism goes: The plural of "anecdote" is not data, it's "anecdotes." And even if this had been a clinical trial, it is impossible for it to be a randomized controlled study for the simple reason we'd need to have at the very least two participants in the study--with one serving as the control. A clinical study with a sample size of two is in itself laughable--the margins of error would be so huge as to make its results practically useless. Hence, a sample size of one is just absurd.
Linda Bily, a reviewer on Amazon.com of Plant's book, likewise apprehends the lack of critical thinking that Plant manifests and has this to say:
The premise that since Oriental women don't consume a lot of dairy products and have less incidence of breast cancer is plausible, but unproven. I shudder to think of the thousands of women who will change their diets based on this book. I am most concerned that the high intake of estrogens and phytoestrogens, especially in the soy products recommended, could be detrimental to some women. There is still controversy in the medical community about the use of soy. If you read this book as an interesting scientific, but unproven, premise, you will be fine. If you take this book to heart, without consulting your medical specialist, you could be opening a can of worms. Dr. Plant is a respected scientist in her field. As a breast cancer survivor and advocate, I question some of her findings. The studies she cites to validate her ideas are older, some of obscure practice and are not widely confirmed. I also take issue with her description of her own breast cancer diagnosis. It returned 5 times according to the author and yet she states that it was an early stage at diagnosis. The tumor on her neck disappeared during chemo and she credits only her non-dairy diet for this shrinkage. She says that it spread to her lymphatic system, but her lymph nodes were clear. The book is interesting reading, but while I do not doubt her personal beliefs or her expertise as an earth-based scientist, I do hesitate to recommend this book to anyone. I am afraid that too many women, looking for a quick fix, will adapt her lifestyle without question. There still is no known cause or cure for breast cancer. Feel free to search alternative options and methods, but please, discuss any changes in your treatment, diet or life with your medical team and make an informed decision.
So, is Jane Plant's hypothesis that dairy products are a casual factor in breast cancer wrong? Certainly not. Let me repeat that in case you think that's a typo. It may be that regular consumption of dairy products are (partly) responsible for breast cancer. My critique above does not imply that Plant's hypothesis is totally off the mark. What is utterly awry are the methods/reasoning by which she reaches her conclusion, which means it is nowhere close to being conclusive. Keep in mind that an argument may have false premises but true conclusions. When the argument contains various fallacies then the conclusion cannot be known to be true. However, if the argument is sound (i.e, the premises are known to be true and the argument contains no fallacies) then the conclusion must by necessity be true. Because Plant does not follow scientific protocol (ie., objective, unbiased methods of testing hypotheses) we cannot have any confidence in her conclusion.
As a scientist, what Plant could have done is applied for a grant and performed randomized, double-blind, controlled clinical trials (RCT) employing at least several dozens of participants. Barring this (for ethical or whatever reason), she could've performed an epidemiological study (just as was done with tobacco use and lung cancer decades ago), although such studies hardly provide the degree of certitude of RCTs. (But since she has no degree nor expertise in medicine I doubt she would've been awarded research money in the first place; thus she should've left testing of this hypothesis to the experts).
It is said that when a layperson makes a mistake in matters of, say, rocket science then that mistake is out of ignorance. But when a rocket scientist commits an error involving rocket science, that's stupidity. Prof. Jane Plant claims to be a scientist. But she made elementary mistakes about hypothesis testing and induction. Now that's utter stupidity.
As we've seen above Plant says of her cancer treatment: "I am living proof that it works." No, Prof. Plant. You're living proof that you failed to learn the essentials of Scientific Method 101. For shame!