THE IMPACT OF DIETARY-PROTEIN INTAKE ON URINARY CREATININE EXCRETION IN A HEALTHY PEDIATRIC POPULATION

Objective: The aim of the study was to investigate the effect of daily protein intake on urinary creatinine (CR) excretion in healthy childr en. Methods: In a cross-sectional study, 24-hour urinary CR excretion rates were measured in 350 children aged 4 to 13 years. Body compositi on was assessed according to anthropometric measurements, and intake o f protein was estimated from dietary records. Results: CR excretion ad justed for fat-free mass (FFM) showed a strong age dependency and corr elated clearly with total protein intake and animal protein intake. St epwise regression analyses revealed that age was the main predictor; h owever, animal protein intake improved the proportion of explained var iance in FFM-related CR excretion. Comparisons of urinary CR output in subgroups of children with low (Ist tertile) or high (3rd tertile) an imal protein intake showed that on average, a difference of about 9% i n CR excretion corresponded to a difference of 1.1 g/kg of body weight per day of animal protein intake. Conclusions: Animal protein intake must be taken into account when urinary CR output is used for evaluati ng body composition in children. Additionally, the finding of a clearl y stronger increase in urinary CR than in FFM with age offers an expla nation for the commonly observed phenomenon of a decreasing ratio of n umerous urinary analytes related to CR during childhood.