Protein toxicity

Protein toxicity is the effect of the buildup of protein metabolic waste compounds due to insufficient kidney function. It can occur in people with pre-existing chronic kidney disease, or those who have lost kidney function due to age.

Definition

Protein toxicity occurs when the body is unable to get rid of the potentially toxic wastes that are generated as a result of protein metabolism. It may be also caused by chronic kidney disease.

Occurrence

Protein toxicity occurs when an individual with impaired kidney function consumes a protein-rich diet, specifically, proteins from animal sources that are rapidly absorbed into the blood stream and are rapidly metabolized, causing the release of a high concentration of toxic nitrogenous waste material.

Effects of a high protein diet

A high-protein diet is a health concern for those suffering from kidney disease. The main concern is that a high protein intake may promote further renal damage that can lead to protein toxicity. The physiological changes induced by an increased protein intake, such as an increased glomerular pressure and hyperfiltration, place further strain on already damaged kidneys. This strain can lead to proteins being inadequately metabolized and subsequently causing toxicity. A high-protein diet can lead to complications for those with renal disease and has been linked to further progression of the disease. The well-known Nurse’s Health Study found a correlation between the loss of kidney function and an increased dietary intake of animal protein by patients who had already been diagnosed with renal disease.[1] This association suggests that a total protein intake that exceeds the recommendations may accelerate renal disease and lead to risk of protein toxicity within a diseased individual. For this reason, dietary protein restriction is a common treatment for patients with renal disease in which proteinuria is present. Protein restricted patients have been shown to have slower rates of progression of their renal diseases.[2]

Several studies, however, have found no evidence of protein toxicity due to high protein intakes on kidney function in healthy people. Diets that regularly exceed the recommendations for protein intake have been found to lead to an increased glomerular filtration rate in the kidneys and also have an effect on the hormone systems in the body. It is well established that these physiological effects are harmful to individuals with renal disease, but research has not found these responses to be detrimental to those who are healthy and demonstrate adequate renal activity. In people with healthy kidney function, the kidneys work continuously to excrete the by-products of protein metabolism which prevents protein toxicity from occurring. In response to an increased consumption of dietary protein, the kidneys maintain homeostasis within the body by operating at an increased capacity, producing a higher amount of urea and subsequently excreting it from the body. Although some have proposed that this increase in waste production and excretion will cause increased strain on the kidneys, other research has not supported this.[1] Currently, evidence suggests that changes in renal function that occur in response to an increased dietary protein intake are part of the normal adaptive system employed by the body to sustain homeostasis. In a healthy individual with well-functioning kidneys, there is no need for concern that an increased dietary protein intake will lead to protein toxicity and decreased renal function.

Symptoms

Unexplained vomiting and a loss of appetite are indicators of protein toxicity. If those two symptoms are accompanied by an ammonia quality on the breath, the onset of kidney failure is a likely culprit. People with kidney disease who are not on dialysis are advised to avoid consumption of protein if possible, as consuming too much accelerates the condition and can lead to death. Most of the problems stem from the accumulation of unfiltered toxins and wastes from protein metabolism.

Kidney function naturally declines with age due to the gradual loss of nephrons (filters) in the kidney. Therefore, a 90-year-old cannot safely consume the same amount of protein as a 20-year-old.

Common causes of chronic kidney disease include diabetes, heart disease, long term untreated high blood pressure,[3] as well as abuse of analgesics like ibuprofen, aspirin, and paracetamol.[4] Kidney disease like the polycystic kidney disease can be genetic in nature and progress as the patient ages.[5]

Diagnosis

A confirmation of kidney failure is often obtained by performing a blood test which measures the concentration of creatinine and urea (blood urea nitrogen).[6]

References

Martin WF, Armstrong LE, Rodriguez NR (September 2005). "Dietary protein intake and renal function". Nutrition & Metabolism. 2 (25): 25. doi:10.1186/1743-7075-2-25. PMC 1262767. PMID 16174292.
Brocklebank JT, Wolfe S (December 1993). "Dietary treatment of renal insufficiency". Archives of Disease in Childhood. 69 (6): 704–8. doi:10.1136/adc.69.6.704. PMC 1029661. PMID 8285787.
Parmar MS (July 2002). "Chronic renal disease". BMJ. 325 (7355): 85–90. doi:10.1136/bmj.325.7355.85. PMC 1123635. PMID 12114240.
Hörl WH (July 2010). "Nonsteroidal Anti-Inflammatory Drugs and the Kidney". Pharmaceuticals. 3 (7): 2291–2321. doi:10.3390/ph3072291. PMC 4036662. PMID 27713354.
Harris PC, Torres VE (2009). "Polycystic kidney disease". Annual Review of Medicine. 60: 321–37. doi:10.1146/annurev.med.60.101707.125712. PMC 2834200. PMID 18947299.
Gowda S, Desai PB, Kulkarni SS, Hull VV, Math AA, Vernekar SN (April 2010). "Markers of renal function tests". North American Journal of Medical Sciences. 2 (4): 170–3. PMC 3354405. PMID 22624135.