With your caveat of "Anectodes != data and whatnot, but by my observations", people don't make rational food decisions when given free money. They tend to spend on snacks and sugar, not on veggies. Unless discipline is enforced, free money is a disaster.

Are you also going to have "free health care" with UBI ? That would be cataclysmic as you would need to also give free diabetic and obesity treatments until end of lifespan.