Replacing animal protein with vegetable protein not shown to improve renal function.
High-protein diets have been shown to accelerate renal deterioration in a number of studies of populations with even mildly reduced kidney function.
Most Western-style diets are high in animal protein and relatively low in plant protein sources such as legumes. Consequently, researchers have suggested limiting animal protein as a way to preserve renal function. Animal proteins have higher dietary quality protein because they have a better balance of the two required sulfur amino acids—cysteine and methionine—than plant protein.
A common misunderstanding is that the total sulfur amino acid content of animal protein is higher than that of plant protein, but they are similar in total sulfur content per gram.
Excessive sulfur-containing amino acid consumption is detrimental whatever the source because their catabolism increases the amount of sulfuric acid generated. Another concern is that because vegetable proteins have poorer dietary quality than animal proteins, a higher intake may be required to maintain adequate protein nutrition.
In spite of these basic facts of nutritional biochemistry, vegetarian diets are being promoted as better for preserving kidney function than omnivore diets. What is the current evidence available for advising patients?
Adam M. Bernstein, MD, of the Harvard School of Public Health in Boston, and his colleagues recently reviewed the literature on vegetable-based diets and kidney function (J Am Diet Assoc. 2007;107:644-650). “Although data on persons with chronic kidney disease are limited,” the authors wrote, “it appears that high intake of animal and vegetable proteins accelerates the underlying disease process not only in physiologic studies but also in short-term interventional trials. The long-term effects of high protein intake on chronic kidney disease are still poorly understood.”
Only a few studies comparing animal and vegetable protein diets have been published. James W.
Anderson, MD, and colleagues (Am J Clin Nutr. 1998;68[suppl]:1347S-1353S) reported findings of an eight-week randomized cross-over study of eight diabetics with proteinuria and moderate renal insufficiency. A decrease in glomerular filtration rate (GFR) was observed both in patients receiving a 1 g/kg animal protein diet versus a 1 g/kg protein diet with one half of the protein as isolated soy protein, suggesting there is no difference in diabetic CKD.
Giuliano Barsotti, MD, and colleagues (Am J Nephrol. 1991;11:380-385) followed patients with non-diabetic nephropathy and moderate-to-severe renal insufficiency on a vegan protein diet at 0.7 g/kg/day for three months. Compared with a conventional animal-protein based diet at 0.6 g/kg, no difference in creatinine clearance was observed.
In a later study, Dr. Barsotti and his collaborators (Nephron. 1996;74:390-394) followed 22 patients with nondiabetic nephrosis transitioned from a mixed animal-vegetable (1.0 to 1.3 g/kg/d) to either a conventional low-protein diet at 0.6 g/kg or a vegan diet at 0.7 g/kg/day. After four to six months, both groups showed a significant decrease in GFR and no effect on proteinuria.