Protein Intake in Renal Disease
ABSTRACT & COMMENTARY
Synopsis: The maxim for renal disease patients should be to feed the patient at the same time as treating the patient for other complications of renal failure.
Source: Pollock CA, et al. J Am Soc Nephrol 1997;8:777-783.
Dietary protein restriction has been considered to be one of the strategies to slow the progression of chronic renal failure (CRF), and protein restriction is often prescribed to CRF patients. However, precise protein restriction can be difficult to recommend unless the spontaneous dietary protein intake (DPI) is known. The authors undertook this study to assess the DPI in patients with underlying renal disease with both normal and abnormal renal function. The effect of dietary advice to increase protein intake after initiation of dialyses was also studied.
DPI was evaluated in 766 patients by determination of 24-hour urinary urea and protein excretion using urea kinetic modeling. Data were analyzed using serum creatinine (Scr) levels. Five hundred sixty-five patients had a normal Scr (< 0.12 mmol/L), and, of these, 385 patients were not advised dietary restriction, while 180 patients were advised to follow a low protein diet. Two hundred one patients had an elevated Scr (> 0.12 mmol/L), and 148 of the patients were advised reduction in DPI.
Patients with normal renal function (mean age, 51.7 years) and no dietary restriction had a higher DPI than those who were advised protein restriction (1.08 g/kg/d and 0.9 g/kg/d, respectively). Likewise, patients with abnormal renal function (mean age, 61.9 years) with no dietary modification had a higher DPI than those with protein restriction (0.93 g/kg/d and 0.87 g/kg/d, respectively).
In both groups taken together, DPI had a direct linear correlation with serum albumin, and the level of renal function, as measured by creatinine clearance, independent of dietary advice. Thus, patients with renal dysfunction had a lower DPI. Inverse correlations were observed between DPI and age, plasma cholesterol, triglyceride, and blood sugar levels.
Fifty-two patients were assessed within three months before commencement of dialysis, and, of these, 47 patients were reassessed at three months after dialysis began and again, at 6-9 months after starting dialysis. Despite advice to increase protein intake at three months, there was no increase in DPI. It took 6-9 months before a significant increase in DPI was noted (1.04 g/kg/d compared to 0.79 g/kg/d at 3 months after starting dialysis).
COMMENT BY KAMALJIT SETHI, MD
This study presents some important data. Patients with abnormal renal function spontaneously reduce protein intake with an adverse effect on nutritional status, reflected in reduced DPI and serum albumin. The fact that this occurs independent of dietary advice is reason for concern. Recent data from the study of Modification of Diet in Renal Disease1 and other studies suggest that protein restriction may not be as uniformly beneficial as originally proposed in retarding renal failure progression. Furthermore, low DPI and malnutrition may become problems because patients may not be able to adapt to higher DPI even after commencement of dialysis, and malnutrition is an important adverse prognosticator in end-stage renal disease.2
What should clinicians do? Is it better to recommend low DPI just in case renal disease progression can be slowed down and suffer the consequences of malnutrition? Or, is it better to maintain nutrition with a USRDA recommended DPI of 0.8 g/kg/d, educate the patient, and commence ESRD treatment when indicated? The choices are clear. A well-nourished patient with a protein intake greater than 0.8 g/kg/d has lesser morbidity and mortality with ESRD than a protein-malnourished patient. The maxim for renal disease patients should be to feed the patient (protein USRDA of 0.8 g/kg/d) at the same time as treating the patient for other complications of renal failure, be it hypertension or heart failure. The well-fed renal failure patient will be healthier, will adjust more quickly to ESRD treatment with a better quality of life, and will have an improved mortality rate.
References
1. Klahr S, et al. N Engl J Med 1994;330:877-884.
2. Kopple JD. Am J Kidney Dis 1994;24:1002-1009.
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