Nutrition and Chronic Kidney Disease

Denis Fouque; Solenne Pelletier; Denise Mafra; Philippe Chauveau

Disclosures

Kidney Int. 2011;80(4):348-357. 

In This Article

What is the Optimal Protein Intake in Maintenance Hemodialysis?

In the seventies, a number of metabolic studies were performed in dedicated research wards to better characterize protein and energy requirements of maintenance dialysis patients. Most of these studies were by the same teams, including a limited number of patients due to the time-consuming nature of research: every time one nutritional parameter is modified (for example, testing 1.0 g protein/kg/day in six patients), a new metabolic equilibrium is to be reached only after 2–3 weeks. Thus, testing three different protein intakes after a baseline period will need at least 2 months of full hospitalization for each patient with daily collection of blood, urine, feces, and dialysate output.[70–72] These constraints explain why so few patients were studied and why some large interindividual needs were identified. As a consequence, the optimal protein and energy needs were defined above the minimal requirements observed in the patient who requested the highest level, whereas some other did well for slightly lower values (safety principle). From these experimental studies, a protein intake between 1.0 and 1.1 g/day (as measured by direct food intake) was associated with neutral nitrogen balance,[70–72] and a general agreement was made upon requirements of 1.2 g/kg/day in maintenance hemodialysis and 1.2–1.3 g/kg/day in peritoneal dialysis. These values were enforced in 2000 by the Kidney Disease Outcome Quality Initiative Nutritional guidelines.[9] However, after some months or years, physicians who started to evaluate their patients' intakes were uncommonly able to reach these values and felt these targets were inadequate.

More recent epidemiological research provided slightly different information. Large prospective reports on thousands of patients showed that survival or body composition did not impair when nutritional intakes were lower than recommended.[73–75] In a French cohort of more than 3000 maintenance hemodialysis patients followed during 30 months between 2007 and 2009 (ref. [76]), mortality was increased only when normalized protein nitrogen appearance was lower than 0.7 g protein/kg/day (Figure 1), whereas no additional mortality was observed for normalized protein nitrogen appearance values greater than 1.5 g protein/kg/day, by contrast to Shinaberger's report.[73] Thus, there is little doubt that low-protein intakes should be avoided in maintenance hemodialysis, whereas larger intakes do not clearly impair survival in these patients.

Figure 1.

Mortality rate of hemodialysis patients based on protein intake. Protein intake (g/kg/day) and 30-month hazard ratio for mortality in a prospective cohort of French hemodialysis patients from June 2007 to December 2009 (n=3000, adjusted for age, gender, serum albumin, body mass index, cardiovascular history, and diabetes; from Fouque et al.,76 with the permission of the National Kidney Foundation). nPNA, normalized protein nitrogen appearance.

It is interesting to note that body composition will not further improve when patients eat above 1.0–1.1 g protein/kg/day. Indeed, in a prospective cross-sectional Japanese study in 129 maintenance hemodialysis patients, lean body mass or subcutaneous/visceral fat was not improved when patients had intakes greater than 0.9–1.1 g protein/kg/day.[74] In another study, two different protein intakes were tested in a crossover design for 40 weeks each (normalized protein nitrogen appearance of 1.01±0.18 vs 0.9±0.14 g/kg/day).[75] Fifty-eight patients were randomized and their energy intake was 28–30 kcal/kg/day. Actual dietary protein intake was 1.15 g/kg/day and normalized protein nitrogen appearance 1.0 g/kg/day in the high-protein intake period vs 0.94 and 0.90 g/kg/day, respectively, during the low-protein intake period. There was no change in body weight, lean body mass, and fat mass in either group, nor was any change in serum albumin during the different intakes for 40 weeks each, a sufficient time exposure to reveal wasting. Thus, in this report, an intake of 0.95 g protein/kg/day or a normalized protein nitrogen appearance greater than 0.9 appeared sufficient to maintain adequate body composition and laboratory values, and there was no greater nutritional benefit from a higher protein intake.[75] With this in mind, recent guidelines have therefore slightly reduced protein requirements to 1.1 g/kg/day based on dietary interviews or 1.0 g/kg/day based on normalized protein nitrogen appearance.[68]

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