The estimation of dietary protein intake in chronic renal failure

Forty-five adult clinic patients with chronic renal failure each supplied a 4-day weighed dietary record, a 24-h urine collection, and a nocturnal spot urine sample. Total nitrogen (N) losses derived from the urines were corrected for proteinuria and non-urea nitrogen excretion. Individual estimates of N intake were compared by correlation and assessing the level of agreement. Daily urea N excretion derived from the spot sample correlated well with the 24-h collection P less than 0.001, but the degree of agreement was poor, mean difference being +1.62 g with 95% limits of +5.7 to -2.47 g. The correlation between the spot-sample-derived N loss and dietary N intake was poor, r = 0.42; P less than 0.05. For 12 patients taking a low-protein diet, N intake correlated well with 24-h urine derived N losses, P less than 0.001, mean difference being +0.59 g, 95% limits +2.39 to -1.21 g. The correlation and agreement was less satisfactory for the subjects who had not received dietary instruction, due largely to individual variation in day-to-day protein intake. Use of spot urine samples is too inaccurate for routine clinical practice. Single 24-h urine derived estimates of N intake are only of value for assessing patients previously prescribed a low-protein intake.

The risks and benefits of a low protein-essential amino acid-keto acid diet

Twelve patients with progressive renal failure were placed on a very low protein diet supplemented by an essential amino acid-keto acid mixture for six to twelve months. Total daily intake was 0.04 g nitrogen/kg and 50 kcal/kg. Eight subjects had a significant change in the slope of reciprocal plasma creatinine, becoming less steep and in two cases positive. GFR did not improve, but in four patients the decline over twelve months was less than 0.5 mliter/min. There were significant falls in blood and urinary urea, serum phosphate PTH and calcium X phosphate product. Body wt decreased during the first three months. Arm muscle circumference fell by 0.9 cm (P less than 0.005). Serum albumin and transferrin levels did not change significantly. Muscle mass and plasma creatinine fell simultaneously in several patients. Creatinine excretion per kg muscle mass, assessed anthropometrically, declined by 21% in the first three months. This diet may slow the decline in renal function in a proportion of patients. However, muscle mass can be lost. Serum protein levels do not accurately reflect nutritional changes. A fall in plasma creatinine may not be due to improved GFR but instead to altered creatinine metabolism.