It was quite fun to see the Movie Ennis enjoying beans EVERYTIME that he was eating them. For normal diets, one needs a little meat protein to go with vegetable protein.
But, when I was in dire straits financially, I ate mostly beans which I cooked myself. The Licensed Practical Nurse and the RN at the VA Out Patient Clinic here in Tulsa, Oklahoma, told me that when I had beans, I should also mix rice with them and that would help with the lack of meat protein. I had never heard of that; but, I do like beans and rice together as a dish.
There are a couple of Biblical Proverbs which are somewhat related to this discussion, "Don't muzzle the ox who threshes the wheat" and "The worker deserves his wages."
In the "ox" proverb, the slaughter and eating a sheep when the food supply was low would fit that category with the guys being the "oxen" and the sheep being the "wheat."
While the movie implies that the boys were being paid a monthly wage, nothing about that is in the book. Aguirre might have just contracted to pay a certain wage for the whole late spring and summer season or so much per month or per day.
A certain percentage loss of livestock, aka the sheep, was expected due to the occasional extreme weather conditions up on the mountain. The sheep which scattered during the movie hail storm was not the fault of Ennis at all. The Chilean shepherds were doing the same illegal thing with their sheep as was being done with Aguirre's sheep or they would not have gotten mixed up together, IMO. Aguirre's sheep were not pastured where they were assigned to be by the Forest Service.