In an analysis of data from the Nurses’ Health Study, a group led by Eric L. Knight, MD, MPH, found that women with mild renal insufficiency had a correlation of higher protein intake with decrease in GFR (Ann Intern Med. 2003;138:460-467). Subanalysis revealed that the consumption of non-dairy animal protein led to greater decreases in GFR than either dairy or vegetable protein; however, high intakes of any protein had deleterious effects.
The differences in protein adequacy of low-animal versus vegetable protein for preventing protein malnutrition is even less studied. Only the 1996 study by Dr. Barsotti’s group examined this possibility; in that study, the researchers observed no change in body weight, serum total protein, serum albumin or serum transferrin over three months in 22 patients placed on the vegan diet.
Since the various high-protein foods differ greatly in amino acids as well as accompanying nutrients, such as iron, zinc, omega-3 fatty acids, and isoflavones, more study is needed to determine if any of these secondary nutrients may affect renal function with longer consumption of animal versus vegetable diets. For example, researchers have reported that consumption of 0.5 g/kg isolated soy protein compared with 0.5 g/kg purified casein for four weeks not only decreased urinary albumin by 9% but also improved the lipid profile of men with type 2 diabetes mellitus and nephropathy (J Nutr. 2004;134:1874-1880).
In another study (Nephrol Dial Tranplant. 2007;22:229-234), researchers substituted 25 grams soy protein for 25 grams animal protein for five weeks in 20 renal transplant patients. Total protein intake was about 1.0 g/kg. The investigators observed no difference in creatinine clearance, urinary protein excretion, and serum albumin, but LDL cholesterol decreased from 136 to 123 mg/dL. Lipid peroxides also decreased.
Overall, the limited research available suggests no advantage of low- and moderate-protein diets with vegetable versus animal protein, but high-protein diets from any food source can be deleterious.