EDIT: Arrgh, I'm an idiot and linked to the wrong study. Here's the correct one: http://onlinelibrary.wiley.com/doi/10.1002/ana.23593/abstract
(Incorrect but very similar study: http://www.ncbi.nlm.nih.gov/pubmed/21568955)
Briefly, this was a prospective observational questionnaire-based study which tracked fat intake of "older" women. The women who reported eating the most saturated fat had the most cognitive decline over 4 years. Those who ate the most monounsaturated fat had the least cognitive decline.
I know, I know, corrolation does not equal causation and questionnaires are notoriously unreliable. But I feel nervous when I see studies suggesting that saturated fat is bad for you, and I see a fair number of them. I find it hard to point others to studies such as the Krauss 2010 meta-analysis (which found no increased cardiac risk associated with saturated fat) when there are plenty of other ones which reach the oppsite conclusion.
Reassure me, please?