So here's the diet the rats got addicted to: "The cafeteria diet consisted of bacon, sausage, cheesecake, pound cake, frosting and chocolate..."
This is also a very high sugar diet! Again fat gets the blame and sugar gets a pass.
It's known that low-carbohydrate/high-fat diets work well for weight loss -- even when unrestricted in calories. The mainstream explanation for this is that the diets are so restrictive in food choices that people voluntarily eat less because they get bored with the food, and create a caloric deficit.
So why is a fatty diet so boring in one case (bacon!) and addictive (cheesecake!) in another?