When considering the levels of phosphorus and other minerals present in the diet, it is important to understand the amount of total phosphorus that is actually bioavailable (i.e., absorbed or available for physiological activity) to the specific situation for which the diet is being developed (e.g., infant formulas, malnourished children, seniors with osteoporosis, etc.). This knowledge is needed by food scientists and nutritionists when determining the appropriate levels of bioavailable minerals to supplement foods to meet a dietary need.
Foods for the human population often are based on various cereal grains. These are an important source of nutrition, due to their complex carbohydrates and their high content of vitamins and minerals. However, it has been found that approximately two-thirds of the phosphorus in grains is stored in the form of phytate, a salt of phytic acid, which is not bioavailable in humans. Therefore, mineral fortification is needed to deliver bioavailable nutrients. A common misconception is that phosphate salts also have low bioavailability. In fact, inorganic forms of phosphate are readily ionizable and available for absorption following ingestion. Even phosphates that are less soluble in neutral pH conditions, such as most calcium phosphates, will dissolve in the acidic pH found in the stomach during digestion. The subsequent absorption across the intestinal wall into the blood allows both the phosphorus and the associated cation, calcium, to be available physiologically. This makes calcium phosphates an excellent choice for calcium fortification.