Phosphorus: the forgotten, essential ingredient: phosphates enhance the nutritional benefits of foods by adding phosphorus, an essential mineral

Prepared Foods, Feb, 2005 by Andrew G. Ebert

As a group, phosphates comprise one of the most important functional segments of food ingredients. These high-quality ingredients can enhance the characteristics and value of the foods in which they are used. Increasing numbers of health-conscious consumers also are interested in choosing foods that provide additional nutritional benefits. By choosing phosphates as functional food ingredients, food manufacturers have the opportunity to enhance the nutritional value of their products through the addition of phosphorus.

Importance of Phosphorus

Many do not realize that phosphorus is an essential mineral for human and animal life. It is fundamental to growth, maintenance, and repair of all body tissues and is necessary (along with calcium and magnesium) for proper growth and formation of bones. In addition, the body utilizes phosphorus in protein synthesis, carbohydrate metabolism, enzyme activation and as a component of nucleotides and nucleic acids (DNA and RNA). The 1997 publication by the National Academy of Sciences updated the Dietary Reference Intakes (also referred to as the Recommended Dietary Allowances) for phosphorus to 500, 700 and 275mg per day for children, adults, and infants, respectively.

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, real nourished 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.

Phosphates as Functional and Nutritional Ingredients

Phosphates are one of the most widely used functional food ingredients. Applications of the various salt forms of phosphates include uses such as leavening agents in baked goods, moisture loss inhibitors in frozen and processed meats, emulsifiers in dairy products, and buffering agents for many different food formulations. The use of inorganic phosphate salts as food ingredients provides a dual purpose: to impart a desired functional effect and to meet a nutritional need by the addition of both phosphorus and many of the possible associated cations (e.g., calcium, potassium, magnesium and iron), which also are essential minerals for human health.

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.

Calcium Phosphates for Improved Bone Health

The current demand by informed consumers for increased levels of calcium in foods continues to rise. It long has been known the intake of appropriate levels of calcium is important to maintain proper bone mass, since bone mineral (hydroxyapatite) is a form of calcium phosphate. Several recent studies by Robert P. Heaney, M.D. at Creighton University (Omaha, Neb.) have underscored the importance of the calcium source used, and the superiority of calcium phosphates in assuring adequate calcium absorption, mineralization and bone formation.

In a 2003 study (Bone, 2003. 32:532), Heaney and Shapiro evaluated the role of phosphorus in calcium intake for bone growth, mineralization and overall growth rate in rats. Calcium carbonate and calcium phosphates also were studied. At equivalent calcium levels, the phosphorus compounds were more effective than calcium only (e.g., from calcium carbonate) in bone growth and overall development. The authors concluded that "in any growth situation, both calcium and phosphorous are needed to support an increase in bone mass." They also concluded that calcium supplementation alone is inadequate for diets low in phosphorus, and that it may even aggravate the phosphorus deficiency. "At the very least," Shapiro and Heaney state, "a phosphorus-containing calcium source would be preferable to a supplement providing calcium alone."

Heaney and Nordin evaluated calcium intake on the absorption of dietary phosphorus in humans in clinical studies completed in the U.S. and U.K. in 2002. They commented that the dominant anions in the calcium supplement market are carbonate and citrate, and that their use is not a problem if phosphorus intake is sufficiently high. However, for many persons--such as the elderly, those with osteoporosis, and people who have nutritionally deficient diets--phosphorus intake may not be sufficient. For them, calcium supplementation should be in the form of phosphate salts.