All four groups of mice gained weight throughout the experiment, with a ?nal body weight greater in the group that ate an unscheduled high-fat diet.

IOW--calories still matter. And you'll gain weight when you eat more calories than you burn (and lose it when you eat fewer).

(btw I presume the insulin reactions among the groups were altered by the macrocomposition of the 4 diets, but this was not sufficient to prevent weight gain when excess calories are consumed)