I came across an interesting study the other day, courtesy of Dr. John Briffa's blog. It's titled "Margarine Intake and Subsequent Coronary Heart Disease in Men", by Dr. William P. Castelli's group. It followed participants of the Framingham Heart study for 20 years, and recorded heart attack incidence*. Keep in mind that 20 years is an unusually long follow-up period.
The really cool thing about this study is they also tracked butter consumption. Here's a graph of the overall results, by teaspoons of butter or margarine eaten per day:
Heart attack incidence increased with increasing margarine consumption (statistically significant) and decreased slightly with increasing butter consumption (not statistically significant).
It gets more interesting. Let's have a look at some of the participant characteristics, broken down by margarine consumption:
People who ate the least margarine had the highest prevalence of glucose intolerance (pre-diabetes), smoked the most cigarettes, drank the most alcohol, and ate the most saturated fat and butter. These were the people who cared the least about their health. Yet they had the fewest heart attacks. The investigators corrected for the factors listed above in their assessment of the contribution of margarine to disease risk, however, the fact remains that the group eating the least margarine was the least health conscious. This affects disease risk in many ways, measurable or not. I've written about that before, here and here.
The investigators broke down the data into two halves: the first ten years, and the second ten. In the first ten years, there was no significant association between margarine intake and heart attack incidence. In the second ten, the group eating the most margarine had 77% more heart attacks than the group eating none:
So it appears that margarine takes a while to work its magic.
They didn't publish a breakdown of heart attack incidence with butter consumption over the two periods. The Framingham study fits in perfectly with most other observational studies showing that full-fat dairy intake is not associated with heart attack and stroke risk.
It's worth mentioning that this study was conducted from the late 1960s until the late 1980s. Artificial trans fat labeling laws were still decades away in the U.S., and margarine contained more trans fat than it does today. Currently, margarine can contain up to 0.5 grams of trans fat per serving and still be labeled "0 g trans fat" in the U.S. The high trans fat content of the older margarines probably had something to do with the result of this study.
That does not make today's margarine healthy, however. Margarine remains an industrially processed pseudo-food. I'm just waiting for the next study showing that some ingredient in the new margarines (plant sterols? dihydro vitamin K1?) is the new trans fat.
Butter, Margarine and Heart Disease
The Coronary Heart Disease Epidemic
* More precisely, "coronary heart disease events", which includes infarction, sudden cardiac death, angina, and coronary insufficiency.