You could do both, have a benefit and a negative, then people could choose what they want to specialise in.

I'd also recommend mixing and matching, so for example increasing charisma in one circumstance increases laziness and in another circumstance increases materialistic. That would cause players to be able to choose what they'd like to excel in, and where they don't mind taking penalties. I also think that you should either get an equivalent positive bonus to negative penalty for an action, or a better positive bonus than negative penalty.

Finally I'd say you'll probably want to make it so that each choice either has a lot of different options so people don't have to choose things they don't like, or a choice where they can avoid stat changes completely. 

Unfortunately all of this relegates the stat system to  a very secondary/minor role in the game, meaning that interesting interactions coming out of being obese or something else will likely be missed by most players as the different negative stats are deemed to be a bad things and players will try to optimise away from it. 

If instead you'd rather the stat system be rather forefront in the game but you also don't want people to feel rather annoyed every time they get hit with a new penalty two alternatives I have are:

 *  having 'skill bundles' where you get a new skill or abililty but it's bundled with a negative trait, and rather than having a slow slider (obesity from 1-100) you just have 'mildly obese' 'obese' 'very obese' stacking skills, each with their own stats. This gives tangible reward at the same time as the penalty, rather than just having 'some numbers go up' and 'some numbers go down', making the whole thing feel a bit more meaningful. 

 * Turning the whole system on it's head and have the negative traits actually be good things, e.g. if you're lazy maybe people pay you more to do stuff because they know you don't want to do it? But instead of having it be an outright boon have it be reflected in world interactions (e.g. talking to characters) and make it very obvious that those bonuses (e.g. extra dialogue options) are a result of having a high penalty skill.

For the last option you'll also need to teach the player really early on about the in-world bonuses, for example having a player start with the lazy stat and show in the first area that they can take a nap in a random bed (only because they have the lazy stat) and give them a bonus (e.g. a new npc pops up) because they did it.