Recent research published in the scientific journal PLOS ONE investigated the diet of Roman gladiators in the second and third centuries A.D. and were able to determine the diet of the gladiators and what appears to have been a Roman era energy drink.
Researchers were able to examine the skeletal remains of 22 Roman gladiators buried in a gladiator cemetery in the city of Ephesos (modern day Turkey) using stable carbon, nitrogen, and sulphur isotope analysis, and determining the levels of inorganic bone elements (strontium, calcium) they were able to workout the main constituents of the gladiator diet.
Interestingly it seems that very little meat found its way into the gladiator diet, instead of the bulk of the diet was made up of beans and Barley. Barley was such a significant part of the gladiator diet but there is evidence of these warriors being referred to as hordearii (meaning Barley eaters), there was also clear evidence that the gladiator diet featured both oatmeal and dried fruit.
However perhaps the most interesting element of the gladiator diet was a drink mentioned by Pliny the Elder, apparently made by mixing plant ashes and vinegar that has been compared to a modern day energy drink by researchers. It seems likely that this drink was intended to be served after fights and possibly after training to remedy body pain and speed healing. It has been suggested that this drink could be part of the reason for the high levels of strontium and calcium found in the skeletons.
Wider analyses has led researchers to state that the diet of the gladiator was significantly different from the diet of the wider population.