There’s a very important part of good science, that correlation does not prove causation. To give a crude example, if I’m eating an ice cream cone and a chimp passing by on his way back to the circus goes out of his way to cross the street just to punch me in the stomach, while the same chimp just minds his own business and keeps walking if I’m standing in the same spot but without an ice cream cone, then one can say that ice cream and abdominal pain is correlated. But then one is missing the point.

This same idea applies to all areas of science, and in some places you’ll find it more prominently than others. Like health research: Studies of religious people consistently find they live longer, healthier lives than the non-religious. Ipso facto, religion increases longevity. Just slightly beneath the surface of that concept is the fact that most religions ask their practitioners to take care of themselves, the body is a temple and all that. Clean livin’ is  the more likely culprit behind above-average aged religious folk than religion itself, but nonetheless the correlation between the two lends itself to a genuine hypothesis; that religion leads to longevity.

A hypothesis can be tested, if its supported it becomes a theory and if it’s ever definitively proven, it becomes a law (as I  understand it). But when you add the public into the mix sometimes a hypothesis is good enough, especially if it makes people say gee whiz. I found recently that seems to be the case with the idea that fat intake leads to heart disease. According to a Men’s Health article I recently came across, the link between heart disease and fats, especially saturated fats, is based on a hypothesis from the 1950s, one that never was supported into the realm of theory and hasn’t held up.

Back in 1953, Dr. Ancel Keys, a physiologist came up with the diet-heart hypothesis, which implicated fat intake and cholesterol specifically as the culprit behind the high prevalence of cardiovascular disease in Americans. Keys dedicated his career to studying how the diet affects health. He also, notably, lived to be nearly 101. During World War II, he led studies on the effect of starvation on American conscientious objectors who “volunteered” as subjects and he came up with the Mediterranean Diet.

Sandwiched in between those highlights was his landmark 1953 paper and his follow up, the 1970 Seven Country Study. In both, he surveyed the rates of heart disease and cholesterol intake among, as the study’s name implies, the population of seven countries. What he found was a strong correlation indeed. As the Men’s Health article author writes:

“The Americans ate the most fat and had the greatest number of deaths from heart disease; the Japanese ate the least fat and had the fewest deaths from heart disease. The other countries fell neatly in between. The higher the fat intake, according to national diet surveys, the higher the rate of heart disease. And vice versa. Keys called this correlation a “remarkable relationship” and began to publicly hypothesize that consumption of fat causes heart disease.”

But the that it was merely a hypothesis was left somewhere behind in the media attention that Keys helped hasten in his public implication of animal fat in heart disease. The problem in that was there was plenty of other data that contradicted or at least undermined that hypothesis. For example, if you look at the results of the 22 countries for which the data was available in 1953 rather than just the six Keys chose, the correlation kind of falls apart. Mexico and Finland had similar levels of fat consumption in the national diet, yet Fins were 24 times likelier to die of cardiovascular disease than Mexicans. And studies of certain African cultures like the Masai, which ate diets extremely high in the animal fat that Keys had fingered as responsible for heart disease had a low prevalence of it among them. It wasn’t until they were transplanted to city life that these tribe members experienced the heart disease we have come to expect from modern life.

This implicates some other culprit, yet that has long been ignored. Apparently we still can’t say for sure that animal fats are responsible for heart disease. And recent research has suggested that intake of “bad” LDL cholesterol also prompts an increase of “good” HDL cholesterol. This is not to say that fat intake is unrelated to heart disease; instead, take it as evidence that we take much for granted.