Protein and the Kidney
Various positive health effects have been attributed to a protein-rich diet, i.e., the intake of significantly higher amounts of protein than what is currently recommended. One example is weight loss while maintaining muscle mass. This has a positive effect on diabetes and hypertension, which are associated with obesity and considered the main risk factors for the development of chronic renal failure [Phillips et al. 2016]. For people with advancing age, a protein-rich diet can reduce the loss of muscle mass and strength [Phillips et al. 2016].
Protein and Kidney Function
High-protein food or supplementation of amino acids increase renal blood flow and glomerular filtration rate of the kidney. This reaction becomes evident about one or two hours after the intake and reaches its peak levels about 30 minutes later [Sharma et al. 2014]. The so-called hyperfiltration represents the renal functional reserve within the body, which is lost in chronic kidney diseases [Helal et al. 2012]. Hyperfiltration occurs in physiological conditions, such as pregnancy, as well as in pathological conditions, such as obesity, diabetes, kidney disease and others. The underlying mechanism varies for different conditions [Helal et al. 2012].
Does a Long-term High-protein Diet Harm the Kidneys?
In the 1980s and 90s, hyperfiltration was discussed as a possible reason for the development of chronic kidney disease. This hypothesis led to the assumption that a long-term, protein-rich diet may also contribute to the development of kidney insufficiency in otherwise healthy individuals. However, no significant evidence was given to support this assumption. Today, the response of the kidney to a high-protein meal is regarded as a physiologically normal, adaptive mechanism, which is similar to the response in pregnancy and does not harm a healthy kidney [Martin et al. 2005].
In their review from 2017, Kamper and Strandgaard gave a comprehensive overview of the safety of long-term (years to decades) protein-rich diets on kidney function [Kamper et al. 2017]. Although the authors concluded that a final assessment is not possible on the basis of currently available knowledge, they also point out that other factors in the diet, such as the protein source, simultaneous intake of fruit, vegetables, salt, phosphate, industrially processed foods, etc., could also play an important role. The authors recommend limiting the protein intake to 1.5 g/kg of normal body weight in the long term, which was merely intended as a precautionary measure.
Protein Intake in Patients with Renal Insufficiency
There is consensus that restriction of protein intake has a beneficial effect on the course of a kidney disease. However, protein shortage has to be avoided as it may lead to harmful deficiencies. The PREVEND Study investigated the influence of dietary protein intake on mortality and renal function in patients with existing renal insufficiency. Whereas the study found no effect on renal function, the risk of cardiovascular events was increased in both the group with the highest and the group with the lowest protein intake. The highest general mortality rate was found in the group with the lowest protein intake [Kamper et al. 2017]. The guidelines of KDIGO (Kidney Disease Global Outcome) recommend reducing protein intake to 0.8 g/kg of body weight in adults with or without diabetes, and with a glomerular filtration rate below 30 ml/min/1.73 m2, i.e., severely impaired renal function. In addition, limiting protein intake to a maximum of 1.3 g/kg of body weight is recommended for adults with chronic renal failure and risk of renal impairment [KDIGO 2012].
Illustrative Material
Kidneys with renal pelvis (Pelvis renalis) and adrenal gland (Glandula adrenalis)
The figure shows human kidneys (Ren), i.e., frontal section and entire kidneys with renal pelvis (Pelvis renalis) and adrenal glands (Glandula adrenalis). The kidneys (Ren) are two bean-shaped organs that belong to the urinary system of the body. They are responsible for the formation of urine which excretes metabolic end products, so-called uremic substances and toxins, from the body. In addition, they regulate the water and electrolyte balance of the body. The adrenal glands (Glandula adrenalis, Glandula suprarenalis) is a pair of two endocrine hormone glands. The adrenal cortex synthesizes steroid hormones (mineralocorticoids, glucocorticoids, and sex hormones), whereas the adrenal medulla releases the neurohormones noradrenaline and adrenaline into the blood.
Last update: March 2023