i've got a "big boned" character i've been playing and so far she hasn't lost any weight(only 3 weeks in so maybe not been playing long enough yet), and she only works out maybe 2-3 times a week. 1 weight session and 2 laps in the pool.
Yeah, three weeks, you would only see noticeable change if you were exercising regularly enough to hit your daily Physical skill cap every day. Even then, you would likely only go down one 'build' so to speak. the OP was describing a consequence of probably daily skill capping for several skill levels & that generally takes more like months. Which will definitely burn the plumpness away as well if you don't eat up to maintain your girlish figure.