Ok, i get the "base fitness" parameter and agree that it is good for gameplay.
What do you think about a "base weight" when you leave a girl alone ?
I might include some sort of base weight system in the future, but it would probably work differently to base fitness. After all, your body doesn't like losing and will try to regain lost weight (yo-yo dieting etc). So the base weight might actually be the highest weight the girl reached in the past.
If base weight will be highest weight reached there is no chance for naturally skinny characters that have to be encouraged to gain weight. That would be a pity because encouragement is such a nice fantasy!
imho base weight would have to be more sophisticated, more like "metabolism" that is very hard to change, if at all.
PS.: even if your body does not like it, you will lose weight if you do not eat, but also lose muscle ie.: fitness. No yo-yo without calorie input.
Yo-yo could be implemented as a "next meal buff" after starving ...
BTW.: What you call "minor improvements" feels like a major milestone!
regards,