Date of publication: October 26, 2015
News & Views
The impact of organic and inorganic phosphate
consumption on serum phosphorus concentration
Abnormal serum phosphorus levels are associated with significant consequences, including cardiovascular events and allcause mortality in both healthy subjects and patients with chronic kidney disease. A recent study by Moore et al[1]
investigated the association between dietary sources of organic and inorganic phosphate with serum phosphorus levels in
a large cohort.
Using data from the National Health and Nutrition Examination Survey (NHANES) 2003-2006, the authors analysed 24hour food recall data from 7,895 individuals, both healthy and exhibiting reduced kidney function. Multiple regression
analyses were used to correlate serum phosphorus levels to clinical and dietary intake variables.
IMPACT OF DIETARY INTAKE
After controlling for estimated glomerular filtration rate, BMI and albumin-to-creatinine levels, a significant increase in
serum phosphorus concentrations occurred with:
Dairy products with inorganic phosphate (parameter estimate (PE) ± SE: 0.07 ± 0.02 mg/dL, P< 0.01)
Dairy products with organic phosphates (PE:0.02 ± 0.01, P<0.001)
Cereals/grains with inorganic phosphates (PE:0.005 ± 0.002, P<0.01)
The impact of inorganic phosphate additives on serum phosphorus levels was considerable, despite being consumed less
frequently than meals with only organic sources.
IMPACT OF CLINICAL PARAMETERS
Patients with an estimated glomerular filtration rate <30 had significantly higher serum phosphorus levels than the
reference group (PE: 0.24 6 ± 0.08, P<0.0001), whilst filtration rates 30–44 and 45–60 were associated with lower
serum phosphorus concentrations.
Being underweight (as measured by BMI <18.5) was also associated with higher serum phosphorus levels, whilst obese
patients with BMI > 35 had lower levels.
In contrast to previous studies[2,3], no association between education level or income on serum phosphorus levels was
found. The authors did not refute the possibility that there is a link between poverty risk and higher phosphorus serum
levels but reported that this was not the case in the NHANES survey.
IMPACT OF OTHER FACTORS
The broad range of serum phosphorus levels seen in this study could not be explained by variations in kidney function or
diet alone, so the authors call for more studies investigating other possible factors, such as Vitamin D levels, FGF 23 or
parathyroid hormone. As highlighted by Hill Gallant in a commentary on this study[4], future studies may also be required
to investigate serum phosphate level variation throughout the day rather than only taking a morning measurement after
an overnight fast. Nevertheless, Hill Gallant agreed with Moore et al that phosphate content should be included on
nutritional labels as it has a significant impact on phosphorus serum levels.
REDUCING INTAKE OF DIETARY PHOSPHATES
Analysing the amount of phosphorus in foods, and its potential effect, is extremely difficult. Phosphorus in various forms
is used not only in additives but in food processing and animal feed, where its impact is hard to quantify. Also, our
absorption of organic and inorganic additive phosphate differs between individuals[5], as does the bioavailability of
phosphorus from meat and vegetables.
As the FDA only requires manufacturers to include phosphorus among the ingredients, and not in the nutritional
information, reading the labels does not help patients identify foods they must avoid. To help combat this, D’Alessandro
and colleagues[6] have recently developed a phosphorus pyramid as an aid. By organizing foods into six levels based on
phosphorus content and bioavailability, the authors have created a visual tool that clearly places foods on a spectrum
ranging from those that are unrestricted to those that should be avoided. Whilst validation studies are required to confirm
its utility and facilitate its adaptation to varying clinical and socio-economic settings, the phosphorus pyramid could prove
to be a valuable tool in the dietary management of patients with chronic kidney disease.
REFERENCES
1. Moore LW, Nolte J V, Gaber AO, Suki WN. Association of dietary phosphate and serum phosphorus concentration by levels of
kidney function. Am J Clin Nutr. 2015;102(2):444-53. doi:10.3945/ajcn.114.102715.
2. Gutiérrez OM, Isakova T, Enfield G, Wolf M. Impact of poverty on serum phosphate concentrations in the Third National Health
and Nutrition Examination Survey. J Ren Nutr. 2011;21(2):140-8. doi:10.1053/j.jrn.2010.03.001.
3. Gutiérrez OM, Anderson C, Isakova T, et al. Low socioeconomic status associates with higher serum phosphate irrespective of
race. J Am Soc Nephrol. 2010;21(11):1953-60. doi:10.1681/ASN.2010020221.
4. Hill Gallant KM. Studying dietary phosphorus intake: the challenge of when a gram is not a gram.
5. Moe SM, Zidehsarai MP, Chambers MA, et al. Vegetarian compared with meat dietary protein source and phosphorus
homeostasis in chronic kidney disease. Clin J Am Soc Nephrol. 2011;6(2):257-64. doi:10.2215/CJN.05040610.
6. D’Alessandro C, Piccoli GB, Cupisti A. The “phosphorus pyramid”: a visual tool for dietary phosphate management in dialysis
and CKD patients. BMC Nephrol. 2015;16(1):9. doi:10.1186/1471-2369-16-9.
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