There isn't mass cannibalism, however the results from a big city is pretty grusome.
1) There isn't enough food within walking distance to feed even a small proportion of the population and what food there is often gets spoiled by the fighting over it.
2) The vast majority of people would rather die than turn cannibal - but a small percentage of a very large number is still a large number.
However, rest assured, this isn't actually shown in the first book. The plot follows groups who were either smart enough to get out of town immediately or were lucky enough to be in isolated areas. The grusomeness happens off stage.
1) There isn't enough food within walking distance to feed even a small proportion of the population and what food there is often gets spoiled by the fighting over it.
2) The vast majority of people would rather die than turn cannibal - but a small percentage of a very large number is still a large number.
However, rest assured, this isn't actually shown in the first book. The plot follows groups who were either smart enough to get out of town immediately or were lucky enough to be in isolated areas. The grusomeness happens off stage.