You may have seen a recent news report that stated that high fat foods were "addictive."
Instead of linking to the report, I'll just link you to the Fat Head analysis.
I admit, I hit the roof when I read about it, because they almost completely ignore the role of SUGAR in the addictive nature of certain foods.
I doubt very much that the rats couldn't stop eating a plain stick of butter. Have you ever tried to eat just butter? I can do it in small amounts, but I guarantee you I couldn't eat the whole stick.
But if you soften the butter and mix it up with sugar, I'm betting you could eat it all juuuuust fine.