High protein diets are all craze. Thanks to the weight loss market and the supplement industry, protein as a macronutrient has domination over the other two macros i.e. fats and carbohydrates. Though we will not go in the detail of the pros and cons of such diet patterns but will stick to the common myth: “high protein intake leads to kidney damage”. A lot of people who know the answer to this, suddenly start blaming the doctors, and their ignorance. I’m sorry, but the docs may be mistaken, but certainly were not wrong, as the real good studies, started pouring in a couple of years back only.
According to researchers Denis Fouque & William E. Mitch, in a 2014 study in the journal Nephrology Dialysis Transplantation, clinical evaluations from 1869 plus experimental investigations from the 1930s concluded that excess dietary protein adversely affected the symptoms of patients. Such reports led to creative efforts in the 1940s to design regiments like the egg-potato diet based on meals that were poor in the number of proteins for patients with chronic kidney disease (CKD).
Athletes, coaches and fitness buffs may eat high-protein diets because they believe that muscle mass increases by eating high protein foods. Another population that frequently utilizes high protein diets consists of people trying to lose weight. Someone trying to lose weight might increase their protein intake to feel fuller and curb cravings.
When protein is metabolized, numerous wasteful by-products are formed. These pass through the millions of blood-filtering nephrons housed within the kidneys, which remove them from circulation and ultimately excrete them from the body through the formation of urine. The more protein that is ingested and metabolized, the harder the nephrons must work to rid the body of these waste products.
Each nephron consists of a coil of capillaries called the glomerulus. Urea is the major excretory product of protein metabolism, it is formed in the liver from amino acids by an enzyme driven process called the urea cycle. When protein is broken into its component parts (amino acids) and metabolized it releases nitrogen which converted to urea and excreted as a waste product. Following the synthesis in the liver, urea released by the liver into the bloodstream and is carried to the kidneys, where it is filtered by the glomerulus and excreted in the urine.
The major changes that take place in the kidneys are an increase in glomerular filtration rate (GFR) (often referred to as “hyperfiltration”), and an increase in the size and volume of glomeruli, which are the functional filtration units of the kidney.
According to a 2004 study in the American Journal of Kidney Disease, by Allon N. Friedman, there are no clear renal-related contraindications to high protein diets in individuals with healthy kidney function. However, High protein diets have the potential for significant harm in individuals with chronic kidney disease and should be avoided if possible.
In a 2005 study in the journal Nutrition & Metabolism, researcher William Martin & team found that there is concern that high protein intake may promote renal damage by chronically increasing glomerular pressure and hyperfiltration. Researchers found that, although excessive protein intake remains a health concern in individuals with pre-existing renal disease, the literature lacks significant research demonstrating a link between protein intake and the initiation or progression of renal disease in healthy individuals. More importantly, evidence suggests that protein-induced changes in renal function are likely a normal adaptive mechanism well within the functional limits of a healthy kidney. However, at present, there is not sufficient proof to warrant public health directives aimed at restricting dietary protein intake in healthy adults for the purpose of preserving renal function.
In a 2013 study in the American Journal of Kidney Disease, a team of researchers led by Dr. P. Stephen from the John Hopkins School of Medicine, analyzed the effect of a high protein diet on kidney function in Healthy Adults, using the OmniHeart (Optimal Macronutrient Intake) Trial.(In brief, the OmniHeart trial was a large-scale, study sponsored by the National Heart, Lung and Blood Institute; the effects of 3 diets with different macronutrient profiles on traditional cardiovascular disease risk factors (blood pressure and blood lipids) were tested. All 3 diets differed in macronutrient composition, but otherwise were similar: a carbohydrate-rich diet (55% of total kilocalories) similar to the DASH (Dietary Approaches to Stop Hypertension) diet, a diet (referred to as the unsaturated fat diet) in which 10% of kilocalories from carbohydrate were replaced with unsaturated fats, and a diet (protein diet) in which 10% of kilocalories from carbohydrates were replaced with protein.All 3 diets were designed to be “healthy” and were low in saturated fat (6% kcal) and cholesterol (150mg/d). Furthermore, the diets provided other nutrients (calcium, magnesium, potassium, and dietary fiber) at recommended levels and were reduced in sodium (2,300 mg/d). The food sources used for protein replacement primarily were vegetable-based. Institutional review boards at Johns Hopkins University, Brigham & Women’s Hospital, and the Harvard School of Public Health approved the study protocol.)For the study 164 adults with prehypertension, were fed each of 3 diets for 6 weeks. Weight was held constant on each diet. The 3 diets emphasized carbohydrate, protein, or unsaturated fat; dietary protein was either 15% (carbohydrate and unsaturated fat diets) or 25% (protein diet) of energy intake. The findings suggested that a higher proportion of calories from protein in healthy adults increases GFR, but whether long-term consumption of a high-protein diet leads to kidney injury is uncertain.
A 2014 meta-analysis study in the journal Plos One, by Austrian researchers Lukas Schwingshackl & Georg Hoffmann, investigated the effects of the high protein (HP) versus normal/low protein (LP/NP) diets on parameters of renal function in subjects without chronic kidney disease. 30 studies including 2160 subjects were included in the meta-analyses. Researchers found that HP diets were associated with increased GFR, serum urea, urinary calcium excretion, and serum concentrations of uric acid. But most of these changes could be interpreted as a physiologically adaptive mechanism induced by the HP diet without any clinical relevance. However, in light of the high risk of kidney disease among obese, weight reduction programs recommending HP diets especially from animal sources should be handled with caution.
A 2015 study by the American Society for Nutrition, by a Spanish research team, led by Marta C. Sanchez, made the following conclusion: “High-protein diets may be appropriate for some individuals, but not for others; hence, specific individual needs, as well as potential negative consequences, must be considered cautiously before such a diet is adopted. The protein content of a diet may be measured using several methods; however, because of the great individual variability in caloric requirements, measuring intake based on the proportion of proteins in total energy intake seems to be the most realistic method. A moderate intake of 1.5 g/kg/d may be easily included in the acceptable protein intake range (AMDR 10–35%) for most individuals. It is important to distinguish between the amount of protein that is required to optimize bone and muscle health and the amount necessary to prevent a deficiency. It is also important to note that high-protein diets are harmful to CKD patients; however, for healthy kidney patients, in view of the findings of several studies, the consumption of a high-protein diet appears to be more advantageous than deleterious. In addition, dietary protein seems to play an important role in other metabolic processes, such as satiety, cellular signaling, and thermogenic and glycaemic regulation in the body. However, this effect becomes important only when consumption is above the RDI; thus, it seems likely that protein intake above the RDI could be advantageous in many situations.”
A 2016 study in the Journal of Nutrition & Metabolism, by Dr. Jose Antonio & team, determined the effects of a high protein diet over a one-year period. Fourteen healthy resistance-trained men completed the study. Subjects consumed their habitual or normal diet for 2 months and 4 months and alternated that with a higher protein diet (>3g/kg/d) for 2 months and 4 months. Thus, on average, each subject was on their normal diet for 6 months and a higher protein diet for 6 months. Researchers found that, in resistance-trained men that consumed a high protein diet for one year, there were no harmful effects on measures of blood lipids as well as liver and kidney function. In addition, despite the total increase in energy intake during the high protein phase, subjects did not experience an increase in fat mass.
A 2018 meta-analysis study in the Journal of Nutrition, by a Canadian research team led by, Michaela Devries, compared high protein (HP) (≥1.5 g/kg body weight or ≥20% energy intake or ≥100g protein/d) with normal- or lower-protein (NLP; ≥5% less energy intake from protein/d compared with HP group) intakes on kidney function. The researchers reviewed 28 studies which showed that, a non-existent or trivial effect of HP consumption on GFR in individuals with normal kidney function. The analysis indicates that HP intakes do not adversely influence kidney function on GFR in healthy adults.
In a 2018 study in the journal Clinical Nutrition, a Malaysian research team, led by Sharmela Sahathevan, investigated the clinical efficacy of whey protein supplement in 126 malnourished patients on dialysis. Patients in the main group received protein powder (27.4g) for 6 months plus dietary counselling while the control group received dietary counselling only. Researchers found that 6-month whey protein supplement feeding improved markers of nutritional status in malnourished dialysis patients with good compliance and tolerance to the product.
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