The human body needs phosphates, which are part of phospholipids, ATP, and numerous other organic compounds necessary for life. However, like salt, retinol, and many other nutrients, there is growing concern that an excessive dietary intake of phosphates can promote metabolic changes that contribute to serious ills. Modern diets high in animal products and grains tend to acidify the blood and yield an acidic (pH <7.0) urine in part because of their sulfur-containing amino acids and relatively high phosphate content. By contrast, eating more fruits and vegetables which are generally high in potassium, calcium and/or magnesium (alkalinizing minerals) and lower in phosphate and sulfur-containing amino acids than animal products, grains, and legumes will reduce the blood acid load and raise urinary pH. This is why eating more fruits and vegetables will counteract the metabolic acid load created by foods such as meat, eggs, beans, grains, and cheeses. An increased acid load (particularly from high phosphate-containing foods) may promote metabolic changes that, over time, contribute to the development of osteoporosis, kidney stones, loss of kidney function, and perhaps type 2 diabetes mellitus (DM), cardiovascular disease (CVD), and some types of cancer. [MS Razzaque. Phosphate toxicity: new insights into an old problem. Clin Sci.2011;120:91-7].
While the metabolic dangers of a more acidic diet and excessive phosphate intake have grown, the commercial food industry has been adding more and more phosphate-containing food additives to processed foods. Phosphates are added to many processed foods like soft drinks as well as more and more refrigerated and frozen meat & seafood. Phosphate additives are also used as anti-caking ingredients, leaving agents, stabilizers, and acidifiers in a growing number of processed foods. Such food additives may be listed in the ingredient list but some may be hidden as "broth". Phosphate additives have doubled in the last 15-20 years. Labeling laws do not require the food industry to list how much phosphate (added and naturally occurring) their products contain.
There is growing evidence that a diet high in phosphates contributes to the loss of renal function and may also contribute to calcification of arteries. It is known that CVD events and mortality both increase as the estimated glomerular filtration rate (eGFR) declines below 60 ml/min. In dialysis patients who have lost nearly all renal function, CVD is increased 10- to 20-fold compared to that of the general population. This represents more than half of the very high 15–25% per year mortality rate seen in patients on dialysis. [Sarnak MJ, Coronado BE, Greene T et al. Cardiovascular disease risk factors in chronic renal insufficiency. Clin Nephrol 2002; 57: 327-3356].
People with even moderately impaired renal function who consume too many phosphate-rich foods will see a marked elevation of fibroblast growth factor-23 (FGF-23) in their blood. Increased FGF-23 is a warning sign of impending renal problems and also contributes to a much greater risk of CVD long before dialysis is required. Physicians often prescribe phosphate binding agents to reduce dietary phosphate absorption, but these binders are often unpleasant to take and can cause serious toxic effects. It might make more sense to reduce intake of milk, meats, cheeses, eggs, and particularly foods with added phosphates and eat more fruits and vegetables. Diets high in phosphates not only elevate FGF-23 but also reduce renal production of 1,25 di-OH-D, which is the metabolically active form of vitamin D. People with elevated FGF-23 who take high doses of vitamin D and calcium will find that much of that extra calcium ends up in their arteries (along with the phosphate) rather than in their bones, which is why failing kidney patients often suffer from osteoporosis/osteomalacia, insulin resistance, and much more CVD. Reducing the dietary acid load has been shown to improve insulin function and slow the progression of chronic kidney disease. [H. Gin, et al. Am J Clin Nutr 1994;59:663-6 & N. Goraya, et al. Kidney Int 2012;81:86-93].
Bottom Line: As the number of Americans with failing kidneys and on dialysis continues to rise, the American food industry continues to add increasing amounts of phosphate-rich additives to a wide variety of foods. Excessive phosphate intake like that of trans fats poses a threat to public health. The required labeling of trans fat has resulted in a marked reduction in the US food supply. It is time the Food & Drug Administration demand that the food industry start putting the amount of added phosphates and total phosphate content on their labels. At the very least, the amount of added phosphates ought to be made public, which could help RDs better plan a reduced phosphate diet for patients with impaired renal function and/or other metabolic problems associated with an excess acid load and excessive phosphate absorption.
By James J. Kenney, PhD, FACN
Stephanie Ronco has been editing for Food and Health Communications since 2011. She graduated from Colorado College magna cum laude with distinction in Comparative Literature. She was elected a member of Phi Beta Kappa in 2008.