@ReneHollyDesign1 I just meant that in Sims 3, if you made a sim lose weight, then didn't make them exercise (whether you were playing them or not), they'd gradually revert to their genetic weight. So Claire gaining back the pounds isn't a surprise.
Sims wouldn't typically gain weight past their genetic weight when inactive unless they're on-screen. For example, a sim might overeat at a party with a buffet, or keep going back to the deep fryer you placed on a community lot. As in real life.
For the Sims 4 system, I feel that, as with many other features, the devs tried to make a more complicated and believable system than in previous Sims games but ended up with something unnatural and annoying to use.
If I were building it, I'd prefer that the weight system was a little less responsive on the margins. A sim eating two standard home-cooked meals a day shouldn't gain or lose weight at all. Weight gain should come from too much food, or lots of junk food; weight loss should come from eating salads or smaller portions. If I were drawing it, I'd have a minimum and maximum line for calories, with some (more) room in between, and sims would have to be outside the boundaries to change weights. The day's exercise should move both lines upwards by an appropriate margin.
I don't know whether it would be feasible to build exercise-like effects into various kinds of everyday movement—whether that would be too much of a hassle or too much data for the game engine to handle. It would be nice if a sim who spent 4 hours gardening got the same benefit as one who spent 90 minutes on the treadmill, but that opens up a lot of possibilities. Chasing around a toddler is hard work, but how do you measure it? Stairs are work too, and running to "go here" is more exercise than walking. Even standing is healthier than sitting, so does standing at the easel or woodworking bench count as a plus? Or is that neutral, and sitting count as a minus? It might be the kind of thing that requires an entirely new game engine to manage.
