Obesity is currently very poorly (not) implemented into the game. This leads to a glaring balance issue with the XXL trait is one of the best starting traits in the game and being essentially free points as well as free calories for the first month in game.
The main problem is that the effects of obesity especially exteme obesity simply aren´t implemented in game. This is in contrast to being underweight/starving which has large reduction to your stats and speed while obesity only has a reduction to your health value. The solution would be to implement the following effect of obesity to make things more balanced:
Scaling encumbrance penalties for being obese or very overweight. That fat will weigh you down and get in the way especially if you are mobidly obese.
Make it harder for obese characters to find and wear clothing. This should be done by making clothing automatically poor fiting if your weigh changes to much (if you go from obese to normal weight or vise versa than your the same clothing just won´t fit you anymore) to making morbidly obese characters unable to wear certain types of armour (I don´t think there exists plate or riot armour for morbidly obese people).
Similar to how straving is potentially deadly being morbidly obese can be deadly in it´s own right. It should be possible to die simply from being to obese either by making a absolute limit to how overweight your character can be before you die of a hartattack. Or more realisticly by introducing a mechanic where if you are above a certain BMI threshold you simply have a chance of dying do to a heart attack if your stamina gets low. With the chance increasing the higher your BMI is over the threshold and the lower your stamina is.