Citrus fruits such as oranges, lemons and grapefruits should not be fed to Bearded Dragons and many other lizards for two reasons. Firstly, they are very acidic and can cause diarrhea. Secondly, because consumption of citrus fruits has potential to disrupt the dietary Ca:P ratio. The Ca:P ratio is especially important to Bearded Dragons and other lizards because for every gram of phosphorus they eat they must also eat a gram of calcium: calcium is directly required in order to absorb the phosphorus through the intestinal wall into the bloodstream.

Calcium deficiency may lead to bone degeneration as the body attempts to attain the calcium it requires from the bones, and most research suggests that the ideal dietary ratio is 2:1 (calcium: phosphorous). Many people wrongly assume that eating citrus fruits lowers the Ca:P ratio because these fruits are high in phosphorus, but in fact the peel of these fruits contains far more calcium than most fruits and even vegetables. However, these fruits are also very high in oxalic acid, which reacts with Ca to form calcium oxalate, a relatively insoluble salt which at the same time removes calcium from the body’s pool of available dietary calcium.