One mostly undisputed observation is that if you get the sweetness just right, an animal will eat more of a chow--and that would probably contribute to the effects in this study.

The diet they called "high fat" vs. the control diet was also entirely purified--I don't know if it contained that much more sucrose, but where the control diet had ingredients like soy meal and hulled corn, the experimental diet had sucrose, soy oil, vitamin and mineral mixes, maltodextrin, etc.