Follow up question, did they have any understanding of the nutrition requirements of an active person (soldier/athlete) versus more pedestrian lifestyles?

I don't know what they would consume to be an athlete, but I do know that the Romans had a working knowledge of nutrition.

In Augustus - The Life of Rome's First Emperor by Anthony Everitt, we are told that Augustus Caesar was always a sickly man. It was predicted that he would die young.

To keep him healthy, he was advised to regularly eat small portions of fruits, olives, vegetables and cheeses. He never drank more than a pint of wine per day and generally avoided meats. It seems that poultry was acceptable.

We don't know what ailed Augustus. The book assumes diverticulitis/colitis/digestive issues. All we know is that it affected him his entire life. It appears that his diet may have helped him battle the illness - he lived well into his seventies.

So, Romans knew some foods were "good for you" and others "bad." They also understood that diet could affect your physical well being.

The Stoic philosopher Epictetus talks about this. It sounds like it was a very demanding regime. They were professionals, not dilettantes, and their training was quite rigorous and specialised.

"I wish to conquer at the Olympic games."

"And I too, by the gods: for it is a fine thing." But consider here what precedes and what follows; and then, if it is for your good, undertake the thing. You must act according to rules, follow strict diet, abstain from delicacies, exercise yourself by compulsion at fixed times, in heat, in cold; drink no cold water, nor wine, when there is opportunity of drinking it. In a word you must surrender yourself to the trainer as you do to a physician. Next in the contest, you must be covered with sand, sometimes dislocate a hand, sprain an ankle, swallow a quantity of dust, be scourged with the whip; and after undergoing all this, you must sometimes be conquered. After reckoning all these things, if you have still an inclination, go to the athletic practice...

If a man is a runner in the long course, there is a certain kind of diet, of walking, rubbing and exercise: if a man is a runner in the stadium, all these things are different; if he is a Pentathlete, they are still more different.

Of course, Epictetus was talking about philosophy, but he must have been a fan of athletics. He uses their training and their competitions many times as examples in his work.

Edit: I forgot to mention that Epictetus often talks about weights, so weight training must have been important.