The Recommended Dietary Allowance of phosphorus is 700 mg/d for adults ≥19 years of age (1). However, the mean daily intake of phosphorus for all age groups exceeded 1000 mg/d in a 2011–2012 analysis of the National Health and Nutrition Examination Survey (NHANES), and over 1400 mg/d in males ≥12 years of age (2). This assessment was on the basis of 1 day of dietary recalls from a nationally representative sample. Although higher (double in males) than the recommended levels, phosphorus was not deemed a “nutrient of concern” in a 2015 Dietary Guidelines Advisory Committee scientific report because intakes were still below the tolerable upper limit of intake of the dietary reference intake (maximum level of a daily nutrient not likely to be associated with an adverse health effect), which, for phosphorus, is 4000 mg/d (1).
Higher phosphorus intakes have been associated to higher serum phosphorus levels in individuals with or without CKD, with limited evidence in those without CKD (1,3). Further, through several epidemiologic studies, higher phosphorus intake and/or levels have been associated with an increased incidence of chronic diseases. These findings have raised public health concerns surrounding phosphorus, leading to a push for an improved transparency on the Nutrition Facts Label, especially because previous studies have shown a strong association between food labeling and a healthier dietary pattern (4).
Phosphorus and Its Additives
Phosphorus in foods can be found as naturally occurring (organic) or as food additives (inorganic) (1). Inorganic phosphorus can also be found in dietary supplements as well as in over-the-counter and prescribed medications, representing an underrecognized source of dietary phosphorus (3).
A major and important difference between these sources is their absorption efficiency in the human gut. Organic phosphorus from meat and dairy sources is estimated to be absorbed at approximately 60%, whereas plant-based phosphorus at <40%. By contrast, inorganic phosphorus added in foods is believed to be more readily absorbed at rates >60% (3). However, no human studies have been conducted to assess the absorption of phosphorus from different dietary sources, or the overall phosphorus absorption rate of a mixed diet with different ratio of processed foods (with phosphorus additives) to organic phosphorus (plant- or meat/dairy-based phosphorus).
Phosphorus additives are used for a variety of reasons; they can, for example, be leavening agents, acidifiers, or taste and color enhancers (1). The Food and Drug Administration (FDA) categorizes them as “Generally Recognized as Safe,” having been deemed “safe under the conditions of its intended use,” without the need of a premarket review and approval by the FDA, but rather by scientific experts aware of the safety of substances added to foods (5). Over 48 phosphorus additives are included in the FDA Generally Recognized as Safe list. Furthermore, >50,000 food products in the United States contain one or more phosphorus additive. These products represent >85% of all food products sold in the United States in the past few years (6).
In addition to being exposed to phosphorus additives through ingestion of food products that contain these chemicals, consumers can also ingest inorganic phosphates in fast foods and restaurant foods (1). Even meat products have added phosphates, making it challenging for patients, such as those on dialysis, to maintain an adequate protein intake (7).
One of the most concerning aspect surrounding the lack of transparency with phosphorus additives is the discrepancy between food composition databases and direct chemical analyses. Indeed, several studies have chemically analyzed the phosphorus content of grocery items and meat products and found alarming discrepancies between their results and what is reported in nutrient databases (1,7). Specifically, the food composition databases underestimate the actual phosphorus content of foods (3,7). Thus, prior analyses using food composition databases, such as the NHANES report mentioned above, underestimate American’s true phosphorus intake.
Phosphorus and Health Outcomes
Phosphorus has been associated with several adverse health effects. Various observational studies link hyperphosphatemia to an increased incidence of cardiovascular disease, osteodystrophy, and mortality (1,3). Similar results have been reported in the general population. As an example, dietary phosphorus intake was associated with increased mortality among 9686 normal adults aged 20–80 years in NHANES. Specifically, those that consumed >1400 mg/d of phosphorus had an adjusted hazard ratio for mortality of 2.23 (95% confidence interval, 1.09 to 4.5) per 1-unit increase in log(phosphorus intake) (8).
The Politics of Phosphorus
In 2014, the Nutrition Facts Label received its first revision in 20 years. The proposed changes were meant to facilitate the understanding of the information provided by the label (e.g., a bigger font for calories, inclusion of added sugars to the total amount of sugar). The FDA received thousands of comments about the regulation, including hundreds from patients with CKD or on dialysis, physicians, dietitians, associations, and foundations, each supporting the inclusion of phosphorus on the label (9). Indeed, the American Society of Nephrology (https://www.regulations.gov/document?D=FDA-2012-N-1210-0251) and the National Kidney Foundation (https://www.regulations.gov/document?D=FDA-2012-N-1210-0275) both urged the FDA to make phosphorus labeling a mandatory regulation, citing research that links high phosphorus levels and phosphorus intakes with morbidity and mortality in the CKD and dialysis population, as well as the general population.
In the final rule published in May 2016, the FDA responded to these comments by stating that the label is not meant to be used by individuals to treat chronic diseases, but rather “[…] to help consumers make more informed choices to consume a healthy diet […].” However, in the same rule, the FDA justified having vitamin D and potassium on the label by stating that they are “vitamins and minerals of public health significance” that were important for bone development and general health, and BP lowering, respectively; that they are underconsumed by the population; and that they are therefore nutrients of concern (9). As such, they were included on the Nutrition Facts Label.
Additionally, on April 2, 2018, a new bill, the Food Labeling Modernization Act of 2018, was introduced in the House of Representatives, and referred to the Committee on Energy and Commerce (10). The bill recommends for phosphorus to be listed on the Nutrition Facts Label, as milligram per serving (10). Although it is currently unclear if this bill will be passed or even considered on the House floor, it is important to applaud the continued effort of our representatives in advocating a policy that is not only essential for the kidney community, but also for the general population.
The food industry opposed the proposed changes to the Nutrition Facts Label. It is safe to assume that any major additional changes to the label might result in an opposition from the food industry and their supporting associations. Working with the food industry to facilitate transparency of phosphorus additives in food products might be a first step toward a larger goal: the inclusion of total and added phosphorus on the Nutrition Facts Label. One such example could be to highlight all of the phosphorus additives in the ingredient list, or make the font bold, as the listing of food additives in the ingredient list is mandatory as per FDA regulations (5).
Dietary restriction of phosphorus and its additives remains a crucial and challenging aspect in the treatment plan of patients with CKD or on dialysis. Patients often report frustration about the myriad of dietary restrictions their chronic diseases bring to their lives. Recently, several studies have associated higher phosphorus intakes in healthy adults without known kidney disease with vascular calcification, cardiovascular disease, and mortality. Future research could address the effects of phosphorus intake on health in a population without kidney disease, through existing longitudinal prospective cohorts; the mechanisms by which phosphorus is associated with increased mortality in the general population; the physiologic differences, including phosphorus absorption and bioavailability, between intakes of organic and inorganic phosphorus; the possible economic effect that a labeling change could have on the food industry and, potentially, the cost of foods; and how the inclusion of phosphorus on the label would affect patients on dialysis.
Although it is disappointing that the new and revised Nutrition Facts Label that can now be seen on food products does not contain phosphorus content, proposed laws, such as the Food Labeling Modernization Act of 2018, are encouraging steps in continuing this conversation.
L.B. received support from the National Institutes of Health/National Heart, Lung, and Blood Institute (grant K23HL133842).
The content of this article does not reflect the views or opinions of the American Society of Nephrology (ASN) or the Clinical Journal of the American Society of Nephrology (CJASN). Responsibility for the information and views expressed therein lies entirely with the author(s).
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