Do you even lift, bro?
One of the most alarming things for me when this game first came out was how quickly all of my played Sims got rather ... large. I mean, no matter what they did all of my sims gained a lot of weight...
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They mostly work out to keep their original body shape (so they rarely push their limits). I use Roburky's Fitness Control mod so that unplayed sims don't lose or gain weight or fitness because I don't like it when their body shape changes too much.
