I’m talking about before we figured out we could grow vegetables and fruits. Early humans are often shown as being fit and in shape, yet our diet pretty much only consisted of meat. We were hunters. So why the hell were they so fit? I thought a healthy diet mattered more than just being active constantly?
You have a false premise. Early humans did not eat primarily meat. It was a well balanced diet of about 65% animal products and 35% plant based. Source
Also, there was less specialization of roles, so people simply did more physical labor than people today, who sit at a desk 8hrs a day.