How much is too much protein, and should we worry about the phosphorus?

The concerns of high protein diets were addressed recently in an article published in the Journal of Renal Nutrition entitled, "High protein diets and renal health:'¹ In this provocative article, several Danish nephrologists discuss the current widespread use of high protein diets (i.e. protein content of more than 25% of energy or more than 2 g/kg body weight per day based on meat and dairy products) to promote weight reduction and better health for individuals in the general population with presumably good kidney function.

Yet, the authors point out that the evidence supporting these notions is quite weak and not without safety concerns. They emphasize several reasons to be concerned about adverse effects of such diets, including glomerular hyperfiltration, the hypertensive effects of a concomitant increase in dietary sodium, and an increase in urinary stone formation. These diet-induced physiological consequences might lead to an increase in the prevalence of chronic kidney disease in the general population without pre-existing kidney disease.

Further, they conclude that until clear-cut evidence for the safety and for the superiority of such diets on human health is established, there are compelling medical reasons to refrain from promoting high-protein diets, in particular those based on meat and dairy products. The Dietary Reference Intake for protein for adults is 0.8 grams of protein per kilogram of body weight per day. So if I weigh 80 kilos (176 pounds) I will need 64 grams of protein a day (80 g x 0.8) for health.² As average Americans, we probably consume two to three times this amount of protein. Is there cause for concern?

Watch for the phosphorus content

One problematic aspect of the use of high protein diets in the general population that was not discussed by these authors, but which many believe merits attention, is the high phosphorus content and the efficient absorption from animal protein sources. Many processed meat sources contain added phosphate to retain juiciness while cooking, which further contributes to the total phosphorus content of meat and dairy products.³ Wherever we have protein, we have phosphorus as they go hand in hand. The result is a growing concern over the safety of our current intake of phosphorus.

Every day, American adults typically consume an average of 1400 mg of phosphorus, an amount that is double the recommended dietary allowance of 700 mg/day and almost triple our estimated average requirement.^{4 5} Concern over high intake stems from evidence associating excess phosphorus intake with the risk of cardiovascular disease, cancer, obesity, hypertension, kidney disease, and bone loss, which has inspired a number of conferences like the one held by the Sackler Institute for Nutrition Science at the New York Academy of Sciences in 2013, "Current dietary phosphorus intake: Are there potential implications for public health?"⁶ The conference brought together leading experts to provide a public health perspective on the implications of high dietary phosphorus intake or elevated serum phosphorus levels for the general population.

In healthy adults with good kidney function, serum phosphorus is regulated by several hormones whose pathways can be disrupted with prolonged excess phosphorus intake or failure of the kidneys to eliminate high serum phosphorus through excretion in the urine. Such disruptions in the hormonal regulation of phosphorus and sustained high levels of serum phosphorus have been shown to promote tissue damage and are associated with cardiovascular disease, bone loss, and loss of kidney function.^4,7,8

Demonstrating that high dietary phosphorus intake is the cause of this tissue damage and disruptive changes in hormone regulation is nevertheless challenging due to difficulty in accurately estimating dietary phosphorus intake from insufficient information on food product labels and other confounders. ⁵

Conclusion

Phosphorus intake seemingly continues to increase as a result of the growing consumption of highly processed foods, especially restaurant meals, fast foods, and convenience foods and will only increase further with high protein diets that are thought to be healthy. The increased cumulative use of ingredients containing phosphorus in food processing clearly merits further study, given what is now being shown about the potential toxicity of phosphorus intake when it exceeds nutrient needs. However, we should not lose sight of the contributions stemming from a marked increase in dietary protein that also warrants further study. -by Peggy Harum, RD, LDN

Acknowledgement

I would like to thank Mona S. Calvo, PhD, for her assistance with this article.

References

Marckmann P et al. High protein diets and renal health, Journal of Renal Nutrition, 25(1) pp 1-5, 2015

Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids cholesterol, protein, and amino acids. Institute of Medicine of the National Academies. The National Academy Press, 500 Fifth Street, N. Washington, DC www.nap.edu.

Calvo MS, Uribarri J. Contributions to total phosphorus intake: All sources considered, Seminars in Dialysis, 26:54-6,2012

Calvo MS, Uribarri J. The public health impact of dietary phosphorus excess on bone and cardiovascular health in the general populations. American Journal of Clinical Nutrition, 98:6-15,2013

Calvo MS, Moshfegh AJ, Tucker Kl. Assessing the health impact of phos? phorus in the food supply: Issues and considerations. Advances in Nutrition 5(1):104-113, 2014

Uribarri J, Calvo MS. Introduction to dietary phosphorus excess and health. Annals New York Academy of Science 1301: iii-iv, 2013

Chang AR, lazo M, Appel LJ, Guitierrez M, Grams ME. High dietary phospho? rus intake is associated with all-cause mortality: Results from NHANES Ill. American Journal of Clinical Nutrition, 99:320-327, 2013

ltkonen ST, Karp HJ, Kemi VE, Kokkonen EM, Saamio EM, Pekkinen MH, Karkkainen MU, Laitinen EK, Turanlahti MJ, lamberg-AIIardt CJ. Associations among total and food additive phospho? rus intake and carotid intimal-media thickness: A cross-sectional study of a middle-aged population in south? ern Finland. Nutrition Journal,12:94-99, 2013