Bioelectrical impedance: effect of 3 identical meals on diurnal impedance variation and calculation of body composition

Background: Bioelectrical impedance analysis (BIA) can be used for estimati ng body composition. Earlier studies showed that the ingestion of meals low ers bioelectrical impedance, but none studied the effect of repeated ingest ion of an identical meal in narrow intervals on impedance measurements duri ng 24 h. Objectives: The objectives were to study the effect on bioelectrical impeda nce of 3 identical meals and to compare the results from single-frequency B IA measurements with those from multiple-frequency BIA measurements. Design: Bioelectrical impedance was measured 18 times during 24 h in 18 hea lthy subjects [10 women and 8 men; (x) over bar +/- SD age: 31.5 +/- 11.7 y ; body mass index (in kg/m(2)): 22.2 +/-2.7]. An identical meal was given a t breakfast, lunch, and dinner. Results: Bioelectrical impedance decreased after ingestion of a standard me al (P<0.05). The decrease in impedance lasted 2-4 h after each meal. The de crease was additive during the day, although it was more pronounced after t he first meal because of the combined effect of rising from the supine posi tion and meal ingestion. This is an important consideration when calculatin g body composition: percentage of body fat varied by 8.8% from the highest to the lowest measurement in women and by 9.9% from the highest to the lowe st measurement in men. The bioelectrical impedance at 50 kHz was identical when measured with multiple frequencies or a single frequency. Conclusion: The ingestion of meals leads to an additive decrease in bioelec trical impedance and thus to a decrease in the calculated percentage of bod y fat.