As far as I am aware there was no such thing as a prenuptial agreement back when I got married and certainly not for ordinary people without millions in the bank. Had there been and with hindsight, I would have insisted that we both signed an agreement that stipulated that neither of us could unilaterally take up vegetarianism or partake in other faddish, choice-restricting diets.
I have nothing against vegetarians. In fact, I respect them and believe that morally they are right. However, they are so annoying to live with. You can't go out to eat as very few pubs offer a vegetarian choice that is interesting and worth paying for (vegetable lasagne being the ubiquitous option). You can't stop off for a MacDonalds on the way home from seeing a movie or any other fast food outlet for that matter. Dinners at home become tediously boring as it is just too complicated to prepare two different meals. Life becomes a lot more expensive as stuff that is good for you is always a lot more expensive than food that is going to kill you eventually. Worst of all, having a vegetarian in the house means, at least, twice the amount of washing-up. Usually, it is more because vegetables seem to require all sorts of fiddly gadgetry in their preparation that are a right pig to clean.
I'm not saying that one's wife turning veggie is grounds for divorce but it is certainly grounds for having a good moan about it on social media.