How dietary constituents affecting the calcium absorption?

Several dietary constituents have an effect on calcium absorption. The differences in fractional absorption from different foods can be partly explained by their constituents. Calcium is poorly absorbed from foods that are rich in oxalic acid or phytic acid. Phytates, present in the husk of many cereals, as well as, in nuts, seeds, and legumes, can form insoluble calcium phytate salts in the gastrointestinal tract. Excess oxalates can precipitate calcium in the bowel.

In comparison to calcium absorption from milk, calcium absorption from phytic acid rich grains is one half and from spinach it is only one tenth. This is so because spinach is high in oxalic acid. Among the dietary factors, which increase calcium absorption, lactose is prominent. In fact all metabolizable sugars have been shown to increase calcium absorption.