Background
Some 13CO2 breath tests require prolonged breath sampling. The study aimed to validate a meal which could be served to subjects without interference with the measured breath 13CO2 profile.
Material and Method
Eight healthy volunteers were examined on three separate days. On two occasions they took equicaloric meals of 320 kcal composed of foodstuffs known to be poor in 13CO: cooked rice (R) or a wheat bread sandwich with butter and ham (S). On the control day they fasted. Samples of expiratory air were taken every 15 min for 6 hours. The 13CO2 concentration in the samples was measured by isotope ratio mass spectrometry. Statistical analysis involved repeated measures analysis of variance (RANOVA).
Results
The intra-subject variability of breath 13CO2 concentration was remarkably low on the three study days, as reflected by mean coefficients of variation (CV) of 0.90+/-0.32%, 0.79+/-0.19%, and 0.80+/-0.34% for the control, meal S, and meal R days, respectively (RANOVA: F2;14=0.296, p=0.75). RANOVA indicated a strong effect of a meal on inter-subject variability of breath 13CO2 concentration (F2;46=390.62 p<0.000001). Post hoc comparisons revealed a mean CV of 1.64+/-0.37% on the control day, 3.62+/-0.18% after ingestion of S, and 3.81+/-0.24% after meal R (both p=0.000128 vs. the control). Nevertheless, with neither test meal did RANOVA disclose at any time a statistically significant deviation in breath 13CO2 concentration from the basal fasted value.
Conclusions
Both the test meals fulfilled the requirement of neutrality as concerns a null effect on the breath 13CO2 profile.

Keywords: Reproducibility of Results, young adult, Food, Fasting, Carbon Isotopes - chemistry, Carbon Dioxide - analysis, Breath Tests - methods