Poor people do not make bad decisions because they are poor, although sometimes they are forced into doing things that are unhelpful by poverty. However poverty, other than extreme poverty, of which there is very little and mainly episodic in this country,is not a good reason for a poor diet. For most people a primarily vegtable based diet is cheaper than one based on cheap processed foods.
The vast majority of those on small incomes live in towns and cities, most of which, with few exceptions will have street markets selling fruit and vegetables far more cheaply than in the supermarkets. Brassicas and root vegetables, apples and bananas are just as good for you as any 'super' fruit or veg and most of us manage to survive without eating strawberries all year round.
Canny shoppers, rich and poor go to markets towards the end of the day when fresh food is reduced even further because traders do not want to take it home.