[Differences between morning and afternoon in the assessment of nutritional status by bioelectric impedance in children] [Article in Spanish]

OBJECTIVE: The aim of this study was to examine if there were differences in the assessment of the nutritional status between values of bioelectric impedance (BI) measured in the morning (08:30) and in the afternoon (17:00). PATIENTS AND METHODS: We have studied 30 boys between 6.5 and 10.9 years of age. Weight, stature, skinfold thickness and total body impedance (Z) were measured at 08:30 and at 17:00 on the same day. RESULTS: In 28 of 30 boys, Z at 17:00 was lower than Z at 08:30. The mean decrease in Z was 4.64% of the morning result (p = 0.0001). At 17:00 there was an increase in total body water (TBW) and fat-free mass (FFM) measured by BI, 0.681, and 0.93 Kg, respectively (p = 0.0001), compared with morning values. We did not find differences between skinfold thickness values in the morning and in the afternoon, except for the suprailiac skinfold, which was a bit larger in the afternoon (p = 0.05). In the morning and afternoon there was a high correlation between FFM measured by skinfold thickness and values of TBW and FFM measured by BI. CONCLUSIONS: Z in boys decrease in the afternoon (17:00) compared with morning values (08:30). This fact must be considered by the pediatrician when IB is used for the assessment of nutritional status in children.