Not much can really be said about the Megalodon's diet.
Mainly because we have never seen them so we have not had
the opportunity to study them. However one fact can come
to clarify some efforts of research towards the Megalodon.
All sharks eat about 2% of their weight each day. With a
normal Carcharias that is less than what humans eat in a
day. Considering the Megalodon's size, it would probably
survive off of 90 pounds of Whale blubber in a day. On
fish or other meat it would need about 70 pounds worth.
The Megalodon most likely fed off of anything half its
size and bigger. Humans would most likely NOT be on the
the Megalodon's menu. The reason for sharks not eating
much is because they are cold blooded, so they don't
have to eat as much as warm-blooded animals do. A lot of
food-intake from warm-blooded animals is what keeps their
bodies warm, however cold-blooded animals can regulate
regulate their body temperature to a certain limit. This
means they require less food. If Megalodon's are still
alive, and if they were to live topside, then they would
most likely feed on the local whale and shark populations.
They may even feed on large schools of tuna and blue fish
as does most species of modern sharks.