I think that food stamps only enforce poverty. People can only use them on food and can't do anything with the ones that remain so they just buy more food. People can't save up by smart purchasing decisions. If you look in the US the most common purchases with them are sodas and sweets.
Follow
Or maybe it doesn't matter 
"SNAP households tend to overconsume calories shortly after benefits are received each month, which can lead to insufficient budget for and foods (especially for healthy products like fruits and vegetables) at the end of the benefit month, resulting in reduced dietary quality"
@matrix
Food deserts are neat, ain't they?
@r000t The study mentions that
Hmmmm
"our results suggest that any reductions in food security are not translating into improved dietary quality for black SNAP households. This finding is consistent with work by Nguyen and colleagues, who report that SNAP participation is not associated with improvements in dietary quality or weight status among black adults regardless of their food security status"