MEASUREMENT OF (CO2)-C-13 IN EXPIRED AIR AS AN INDEX OF COMPLIANCE TOA HIGH-CARBOHYDRATE DIET NATURALLY ENRICHED IN C-13

The aim of this study was to determine whether breath (CO2)-C-13 measu rements could be used to assess the compliance to a diet containing ca rbohydrates naturally enriched in C-13. The study was divided into two periods: Period 1 (baseline of 4 days) with low C-13/C-12 ratio carbo hydrates. Period 2 (5 days) isocaloric diet with a high C-13/C-12 rati o (corn, cane sugar, pineapple, millet) carbohydrates. Measurements we re made of respiratory gas exchange by indirect calorimetry, urinary n itrogen excretion and breath (CO2)-C-13 every morning in post-absorpti ve conditions, both in resting state and during a 45-min low intensity exercise (walking on a treadmill). The subjects were 10 healthy lean women (BMI 20.4 +/- 1.7 kg/m(2), % body fat 24.4 +/- 1.3%), the C-13 e nrichment of oxidized carbohydrate and breath (CO2)-C-13 were compared to the enrichment of exogenous dietary carbohydrates. At rest the enr ichment of oxidized carbohydrate increased significantly after one day of C-13 carbohydrate enriched diet and reached a steady value (103 +/ - 16%) similar to the enrichment of exogenous carbohydrates. During ex ercise, the C-13 enrichment of oxidized carbohydrate remained signific antly lower (68 +/- 17%) than that of dietary carbohydrates. The compl iance to a diet with a high content of carbohydrates naturally enriche d in C-13 may be assessed from the measurement of breath (CO2)-C-13 en richment combined with respiratory gas exchange in resting, postabsorp tive conditions.