Oxalates are compounds derived from oxalic acid and found in
foods such as spinach, kale, beets, nuts, chocolate, tea, wheat bran, rhubarb, strawberries and herbs such as oregano, basil, and parsley. The presence of oxalates in spinach explains why the iron in spinach is not absorbed. In fact, it is reported that the iron from spinach that does get absorbed is probably from the minute particles of sand or dirt clinging to the plant rather than the iron contained in the plant.