Background: The monitoring of energy and protein intake is considered fundamental in uraemic patients. However, in the clinical practice only protein ingestion is indirectly evaluated by the protein catabolic rate.
Methods: In a cross-sectional study we evaluated the relationship between caloric and protein intake of 29 stable chronic haemodialysis patients (18M, 11F, mean age 49 +/- 17 years, 68 +/- 6 months on maintenance haemodialysis), and the validity of protein catabolic rate determination. Normalized protein catabolic rate was obtained according to Sargent's formula, and Watson's equation was used to calculate urea distribution volume. Caloric and protein intake were recorded during a 3-day period, and average daily ingestion of nutrients was calculated using a computerized diet analysis system.
Results: A greater reduction of daily energy intake (26.8 +/- 11.9 Kcal/kg bw) than daily protein intake (1.02 +/- 0.4 g/kg bw) was observed. Fifty-nine percent of patients had low protein intake while 86% of patients had lower caloric intake than recommended. An inverse relationship between age and protein (r = -0.65, P < 0.001) or caloric intake (r = -0.67, P < 0.001) was observed. Negative relationships between daily protein (r = -0.60, P < 0.01) and also caloric intake (r = -0.39, P < 0.05) and the ratio between the urea generation rate and the total dietary nitrogen were found, indicating that in patients with low nutrient intake the nitrogen balance tends to be negative. Normalized protein catabolic rate was directly correlated with protein intake (r = 0.77, P < 0.001). A protein catabolic rate cut-off of 1 g/kg bw correctly identified all patients with normal daily protein intake, and 14 of 17 patients with deficient daily protein intake (< 1 g/kg bw). Thus in only 10% of haemodialysis patients an imbalance between both parameters was observed. Moreover, patients with a daily protein intake lower than 1 g/kg bw were older and showed lower BUN and protein catabolic rate values than their counterparts.
Conclusions: Nutritional abnormalities are frequently found, even in apparently clinically stable patients on chronic haemodialysis. Caloric rather than protein undernutrition is the major abnormality of their wasting. Inadequate intake of proteins and calories appears more commonly in older patients, and in association with lower BUN and protein catabolic rate values. Although normalized protein catabolic rate shows a direct correlation with a daily protein intake, the identity line shows that when daily protein intake was lower than 1 g/kg bw, it was overestimated by protein catabolic rate. Conversely, when daily protein intake is higher than 1 g/kg bw it is underestimated by the protein catabolic rate. This relationship should to be considered when interpreting the protein catabolic rate in a clinical setting.