There have been many studies looking at this phenomenon. One hypothesis is that this is due to "food deserts" where the lack of access to fresh foods leads to

There have been many studies looking at this phenomenon. One hypothesis is that this is due to "food deserts" where the lack of access to fresh foods leads to over-reliance on processed foods for caloric needs. It is no coincidence that there is also a strong correlation between food deserts (at a national and local level) with lower income. The solution probably isn't banning specific foods, but to solve the access problem and address socio-economic factors. Better health and nutrition education may also be key.