Did they really have mostly meat though. They were hunters and gatherers. The seeds, roots, nuts, fruit and so on the women gathered probably supported the family much of the time. When the hunters did manage to bring down an animal, there would of been alot of meat to go around and almost feasting. Some of the meat may of been dried and stored, but for the most part they probably survived off the gathered foods. They also got a ton more exercise everyday just surviving. It's hard to compair a modern humans lifestyle to a group that may of walked from sunup to sunset, who ran for miles to catch prey or avoid becoming it.