I hate to even allow for the possibility that I might agree with worm-brain, but he might have a point.
Revisionist History did an episode about this.
There was a researcher who wanted to prove that animal fats led to increased cardiac disease and earlier death. He set up in an institution (I think an old folks home) and split the population in two. One half got their meals made with animal fats, and the other half got all their meals made with vegetable fats.
He was partly right. People who got animal fats had an increase in cardiac disease. However, the people who got vegetable fats were dying earlier.
The researcher didn't like the result so he didn't publish. His son found the data after his death and released it.
That's interesting, however it sounds like a flawed study because it's a small data set that could be influenced by a number of variables.
Another way to look at it is by the 'butter vs olive oil' map of Europe. Italy and Spain have the highest life expectancy rates in Europe, Romania and Bulgaria have the lowest.
To be clear, I'm not actually saying that this map is proof, just pointing out that it's easy to find correlation either way.
I checked the link to the study (which I didn't realize was shared from the Revisionist History site), and I was incorrect about the scale:
Setting
One nursing home and six state mental hospitals in Minnesota, United States.
Participants
Unpublished documents with completed analyses for
the randomized cohort of 9423 women and men aged
20-97; longitudinal data on serum cholesterol for the
2355 participants exposed to the study diets for a year or more; 149 completed autopsy files.