Cost affects what we eat. As a society, we have the power to change what’s affordable. So, let’s tax junk, and subsidise nutritious food to make it cheaper, so those with less don’t need to turn to junk. 
Fight temptation, and reduce social inequalities! Just look at the sugar tax! We taxed sugar, and companies put less in soft drinks. And the group who had the biggest drop in sugar consumption were from areas of high deprivation.