Why Is It More Difficult To Absorb Calcium From Vegetables Compared To Milk?

Vegetables contain other substances ~ namely phytic acid and oxalic acid ~ which prevent the body absorbing calcium efficiently in the digestive system. These chemicals, which occur naturally in green leafy vegetables, bind to calcium forming a complex that does not pass easily through the wall of the small intestine.

The effect of phytic acid and oxalic acid is confined to the absorption of calcium from the vegetables concerned. They do not affect how well calcium can be absorbed from other foods eaten at the same time.

Spinach, sweet potatoes, rhubarb and green beans are all high in oxalic acid. Whole grain bread, beans, seeds, nuts, grains and soy products all contain phytic acid.

The fibre from wheat bran contains a third calcium absorption inhibitor ~ phytate. People who eat large amounts of wheat bran can suffer calcium absorption problems but, in a normal balanced diet, this rarely has an impact because the amount of fibre is not that large.