Dragons must have to eat a LOT. A huge-sized dragon might weight in the range of 1800-2200 kg (4000-5000 lbs) and would likely have to consume meat equal to a human every day to gain enough calories. Or, excluding bones and such, half to a third of the meat from a cow. A dragon could devastate the ecology of a region.

Of course, dragons are the alpha predator to end all alpha predators and could probably feed on animals that normally have no fear of predation, such as lions, elephants, and hippos.