If you are a health-savvy consumer who reads labels at the grocery store to scope out calories, fat, sugar, and fiber, it’s a good idea to note which foods contain added phosphates, too. A study from Houston Methodist Hospital suggests too much phosphorus in the form of phosphates artificially added to processed foods could harm your health.
Phosphates, comprised of phosphorus and oxygen molecules, are found naturally in a host of foods, including chocolate, beans, chicken liver, beef liver, carp, cheeses, and oysters. The phosphates added to processed foods in the form of salts are used as preservatives and thickening and leavening agents in countless products, ranging from cake mixes and dairy products to cereals.
Phosphorus isn’t normally a villain in the body — at least, not in excess. It’s an important mineral for many physiological processes and helps regulate muscle and nerve function. Along with calcium, phosphorus builds strong bones, too.
Normal working kidneys remove extra phosphorus in the blood. So, unless you have chronic kidney disease, it’s long been assumed that having a lot of phosphorus in your diet shouldn’t pose a serious health problem for most people.
However, the Houston Methodist Hospital research concludes the phosphorus you take in from phosphate additives is another story and may damage kidneys and other organs. Unlike phosphates that occur naturally in food, phosphate additives can cause phosphorus to spike to potentially dangerous blood levels.
"Excess phosphorus has adverse effects on patients who already have kidney disease but it can also cause kidney problems," said Wadi Suki, MD, director of Houston Methodist Hospital's nephrology fellowship program and the report's lead investigator. "High phosphorus in blood is associated with increased patient mortality, increased blood vessel stiffening, as well as increasing the rate of calcium deposition in heart valves. This calcium comes out of bones and, therefore, weakens bones as well as damaging kidneys.”
For their study, the researchers zeroed in specifically on phosphates artificially added to food to see if they have the same impact on blood levels as similar amounts of naturally-occurring phosphates.
"We are seeing an increase in the proportion of Americans who have kidney disease, but we have no good explanations why. We thought that it might matter how the phosphates exist in different foods, and how we absorb them," explained Linda Moore, RD, director of clinical research programs for Houston Methodist Hospital’s Department of Surgery and the report's lead author.
The investigators looked at data on nearly 8,000 people who participated in the National Health and Nutrition Examination Survey, a U.S. Centers for Disease Control and Prevention project, to see what foods the research subjects ate between 2003 and 2006 and how their diets affected blood phosphorus levels. The researchers also studied results from lab tests that measured participants’ blood phosphate levels and kidney function.
The results showed that people who ate dairy products and cereal and grain-based foods that contained artificially added phosphates had the most significant increases in blood phosphate levels. Although eating a lot of dairy foods that didn’t contain added phosphates also raised blood phosphate levels, it was a less significant increase.
"The study suggests people should be more aware of what they eat," said Moore. "The Institute of Medicine recommends 700 milligrams of phosphate per day and we think that's a good number. What we were seeing in this study was twice the consumption of that amount for a lot of people. Too much phosphate is concerning to people who are healthy — but it is of special concern to people who already have kidney damage or chronic renal disease."
The U.S. Food and Drug Administration (FDA) doesn’t require food producers to list on labels whether phosphate is naturally occurring or artificially added. In fact, reading labels won’t guarantee you’ll know how much phosphate a product contains. The FDA doesn’t require food producers to quantify the phosphate amounts.
"We believe the FDA can reconsider how it requires food producers to describe phosphorus and phosphate additives," said Suki, who is a former president of the American Society of Nephrology. "An educated consumer can make better dietary choices."
For now, he added, if you aren't sure which foods contain added phosphates, concentrate on the outside aisles at grocery stores, where there is usually fresh food. Middle aisles typically contain more processed convenience foods.
"Pancake and 'quick bread' mixes and processed cheeses often contain a lot of inorganic phosphate, so those should be consumed less frequently," advised Moore.
November 10, 2015
Christopher Nystuen, MD, MBA