Alright so I tested it again and the same thing happened. Character was 30 when got Temp Immobile. She spent 10 years that way asking her servants to pamper her and very early on got big enough to trigger the “Too fat to fit in a Barn” event. Here are her stats right before she tried to go back to normal:
Then it took almost 5 full years of her trying to starve herself to get her body back before she finally lost the temp_obese Trait. As you can see, I have most of the various levels of body part size flags, but not all of the them. She started this adventure with lvl 1 meaty thighs before become immobile.
Now as you can see her fatty power knows no bounds and has ALL the fat focuses. Truly she has ascended into a super chonk god super chonk.