So, having played a bit on the station, I tried out the Obesity disability a decent amount. And I have to say, while it's annoying to move at such a crawl, for more sedentary jobs the Obesity disability really isn't too much of a problem, especially with not having to eat as much. I think it should be more of a genuine trade-off with more interaction with it and medical. so here's my suggestion.
Obesity, on top of making you slower, should increase your heart rate. I'm thinking somewhere north of 80. On top of that, there ought to be a ticking malus for being obese - sugar makes you diabetic easier, and every minute adds a small amount of damage to your heart. It ought to be balanced so that around 40 minutes-an hour, it gets to be a real problem, and can result in full cardiac arrest.
I basically think it should be balanced as so: Obesity lets you eat less, but at a cost to your health, and enough of an annoyance to the medical staff that they have a mechancial reason to tell you to drop the pounds. The last thing they want to be dealing with during a terror spider invasion is a civvie who ate everything the kitchen put out because he was bored. Of course, that'd basically be on him as a player. My observation is, not many people sit around and eat to that amount, so it wouldn't be a massive roadblock to the playerbase. It'd be more of an available route for RP that gives an extra layer of life to the station. It could even result in CMO's wanting to be damn sure that they won't have to deal with it that they start doing physicals - a good opportunity for antags to strike a big group of people, and a good minor action for slower extended shifts.
I hate to be so scant on coding advice, but I've coded for paradox mods, and not so much for this.If I had to take a wild guess, it's probably just a matter of ripping, say, the alcohol toxins damage and flipping it around to the tag for Obesity, but tying the damage going away not to waiting the damage out, but more to not being obese+overweight anymore.