(Excerpts from Medscape): Even a high-protein diet, often recommended to lose weight or build muscles can be harmful to normally functioning kidneys as per two separate new studies from the Netherlands and Korea, published online in Nephrology Dialysis Transplantation. Many earlier studies have shown that a high-protein diet may harm kidney function, and this is why doctors recommend kidney patients a low-protein diet.
The high-protein culture (Atkins, Zone, South Beach, and Ketogenic diets) involve daily protein intake of 20% to 25% or more of the total daily energy intake. As per the studies one should avoid recommending high-protein intake for weight loss in obese or diabetic patients, or those with prior cardiovascular events, or a solitary kidney if kidney health cannot be adequately protected.
1. In the Dutch study, Kevin Esmeijer, MD, of Leiden University Medical Center, the Netherlands collected dietary data using a food frequency questionnaire from 4837 patients 60-80 years of age with a history of heart attack involved in the Alpha Omega Trial. At baseline and 41 months follow-up, serum cystatin C (cysC) and serum creatinine were measured from stored blood samples. The mean age of the cohort was 69 years and mean estimated glomerular filtration rate was 82 mL/min/1.73m2. Compared with the general population, patients with a history of heart attack have double the rate of annual decline in kidney function and thus are at higher risk for chronic kidney disease. For the entire cohort, mean total protein intake was 71 g/day, of which approximately two thirds was from animal protein and the remaining third from plants.
Analyses indicated that the total amount of protein intake per day was inversely associated with the annual rate of kidney function decline. The annual change in eGFR was doubled in patients with a total daily protein intake in excess of 1.20 g/kg ideal body weight, compared with an intake less than 0.80 g/kg.
Specifically, the annual change in eGFR in those with the highest total daily protein intake was –1.60 mL/min/1.73m2 compared with –0.84 mL/min/1.73m2 for those with the lowest total daily protein intake.
And for each extra daily intake of animal protein of 0.1 g/kg ideal body weight, there was an additional decline in eGFRcysC of –0.12 mL/min/1.73m2 per year.
Subgroup analyses also indicated that the association between protein intake and decline in eGFR was threefold stronger in patients with diabetes compared to those without diabetes.
2. In the Korean study, Jong Hyun Jhee, MD, of the Institute of Kidney Disease Research, Yonsei University, Seoul, and colleagues analyzed the effect that a high-protein diet had on renal hyperfiltration and declining kidney function in 9226 participants from the Korean Genome and Epidemiology Study.
Patients were classified into quartiles of daily protein intake as assessed by a food frequency questionnaire. The mean age of study participants was 52 years and the mean follow-up was 11.5 years.
Among the four quartiles of daily protein intake, the prevalence of renal hyperfiltration was significantly higher among those in the highest quartile of protein intake, at 6%, compared with 5.2% among those in the lowest protein intake quartile.
And the annual mean decline in eGFR was again highest, at –2.34 mL/min/1.73m2, among those in the highest quartile of daily protein intake, compared with –2.01 mL/min/1.73m2 among those in the lowest quartile of protein intake.
Rapid decline in kidney function is defined as a decrease in eGFR of > 3 mL/min/1.73m2 per year. They found that those in the highest quartile of protein intake had a 32% greater risk of experiencing a rapid decline of eGFR per year compared with those in the lowest quartile.
They also found that the faster drop in renal function happened only among those with pre-existing hyperfiltration. These findings indicate that a higher intake of protein may be an independent risk factor for renal hyperfiltration that can accelerate deterioration of kidney function.
The recommended dietary allowance for protein intake is only 0.8 g/kg/day and the requirement for protein is likely even lower, at only about 0.6 g/kg/day, provided adequate essential amino acids are consumed. However, most adults in Western societies eat 1.0 to 1.4 g/kg/day of protein. Protein intake may be as high as 20% to 25% or more of the total energy source they add — considerably higher than the 10% to 15% recommended by most guidelines.
Emerging data across individuals and populations suggest that glomerular hyperfiltration associated with a high-protein diet may lead to a higher risk of de novo CKD or may accelerate progression of pre-existing CKD.
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