Protein toxicity with proteinuria can result in those with preexisting kidney disease, or those who have lost kidney function due to age.
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.
Protein toxicity occurs when an individual with impaired kidney function consumes protein rich diet. Specifically proteins from animal sources that are rapidly absorbed into the blood stream and are rapidly metabolized causing the release of high concentration of toxic nitrogenous waste materials.
Effects of a high protein diet
A high protein diet is a health concern for those suffering from renal 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 cause the kidneys to be unable to metabolize the protein adequately and subsequent toxicity may occur. A diet high in protein 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. 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.
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. 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.