Sure, maybe. However, if you're tired of chicken and rice you are not going to find a gladiators diet to be a change for the better. Textual evidence, anecdotal evidence and isotope analysis of gladiator bones all suggest the same thing. The gladiators were almost entirely vegetarian and ate a diet consisting largely of barley, beans and various legumes. They also drank a kind of supplement made from ash and vinegar. While their diet is relatively high protein and energy rich, it is made for someone who trains a lot.

This kind of diet is meant to keep you energized through hours and hours of training almost every day. If you eat this and hit the gym for an hour 3-4 days a week in an otherwise largely sedentary and inactive western lifestyle you are going to get fat. Also, if you want to eat barely mashed in water, a kind of cold porridge basically, be my guest, but I doubt you'll find the kind of dietary variation you're looking for here.

Karl Grossschmidt popularized a theory about gladiators having a "protective layer" of fat but he bases it almost entirely on his isotope analysis and the effect that diet would have on someone today. I personally believe he is wrong and fails to properly account for just how active the lifestyle of a gladiator was. Professional athletes today also eat diets that sometimes goes up to 10-12kcal per day, often with carb laden foods that are relatively high in sugar, but they do not get fat simply because they also burn off 10-12 kcal per day.

Modern nutrition is simply better than anything the gladiators had on hand and I am fairly certain that had whey protein been readily available, cheap and available in all flavours imaginable, they would have used that too.