In Woody Allen’s classic film “Sleeper,” released in 1973, a health food store owner from the 1970s is frozen and wakens decades later to a new world. In the following exchange, his doctors discuss his dietary needs:

“Has he asked for anything special?”

“Yes, something for breakfast. He requested something called wheat germ, organic honey and Tiger’s Milk.”

“Ah, yes; those are the charmed substances that some years ago were assumed to have health-giving properties.”

“You mean there was no deep fat? No steak, or cream pies or hot fudge?”

“Those were thought to be unhealthy, precisely the opposite of what we now know to be true.”

The bit was funny at the time, and has become even funnier in succeeding years as one dietary Holy Grail after another has been grasped and cast aside by an American public obsessed with novel diet regimes.

One day, for instance, coconut and palm oils were a staple in fast-food frying because they do not burn and decompose into toxic substances, as most oils do, when extreme heat is applied. The next day, their high saturated fat levels were decried and refined oils from other plant sources or hydrogenated oils like Crisco were substituted. Then it turned out that this refining and hydrogenation makes the substitutes even more unhealthy then the tropical oils. Most recently, coconut oil is back, now with claims that its medium-chain fat molecules are actually so healthy for you that it’s being marketed as a nutritional supplement. What will they think next week? Stay tuned.

The question of diet has become controversial on our own pages recently with regard to the issue of dairy products, especially the claim that eating animal products of any kind is unhealthy for everybody, supported in one letter by a reference to a book by T. Colin Campbell called “The China Study.” The book, based on an extensive set of statistics collected by Cornell and Oxford universities in 65 provinces in China in 1983/84 and 1989/90, concludes that the consumption of animal protein is highly correlated with various kinds of disease, including cancer and heart disease, and that therefore everyone should avoid eating it entirely.

But a very little digging reveals that one can examine the exact same data set as Campbell and come up with some quite different conclusions. A critique at rawfoodsos.com/2010/06/01/a-closer-look-at-the-china-study-meat-and-disease/ (which, as you will see, is not unfriendly to Campbell in every respect) lets the reader look at the same raw data Campbell was working with, and argues that in many cases the correlations in the underlying study do not justify Campbell’s blanket conclusions.

For instance, the raw data set does show that there is a positive correlation between the consumption of animal protein and hypertensive heart disease. But there is also a positive correlation—of exactly the same degree—between eating plant protein and the incidence of heart attacks and coronary heart disease. In other words, at least as far as this particular data set shows, meat protein may aggravate one type of cardiovascular disease; plant protein may aggravate another.

The raw data also do not seem to support claims of a general correlation between consuming animal protein and the occurrence of cancer. Of 14 cancers studied, none show a statistically significant relationship with the consumption of animal protein, either for good or bad. The consumption of plant protein shows only one statistically significant correlation with cancer: eat more plant protein and you are less likely to get nasopharyngeal cancer.

That’s only one tiny sliver of the data Campbell deals with, and we’re not trying to make up anybody’s minds for them on the question of plant vs. animal food in diets. But we recommend a visit to the above site, including its comment strings (in which there are both defenders and critics of Campbell) as a good way to get an idea of how deeply complex these matters are, and how unsuitable popular simplifications or generalized conclusions are to their nuanced nature.

There could be a variety of reasons to suggest that people shift the proportions of plant and animal food in their diets. But when it comes to sweeping claims about the ideal diet from a health point of view—especially when they rule out entire food groups or advise mega-doses of others—caution is warranted. If you see one nutritional theory, it’s a good idea to seek out the opposition view and find out what data support both sides—double blind placebo studies (which does not describe “The China Study”) are considered scientifically the most conclusive.

Then pay attention to how your own body reacts to different diets and draw your own conclusions.