I think this line of research is necessary in helping us (society) understand ourselves better. Although I've not been poor myself, the ongoing mental stress/strain when met with challenges in which I feel I stand a high chance of failure (e.g. job interviews when I was a new graduate, finding a PhD advisor, submitting first paper for publication) has led me to making poor diet, exercise, and sleep decisions. I would imagine that the poor are faced with an even greater amount of stress in terms of food security, relationship strain, and being cast in a negative light by people around them; making it, as you put it, physiologically harder to make good decisions.