Breath 13CO2 background enrichment during exercise: diet-related differences between Europe and America.

A traditional North American diet contains a high percentage of carbohydrates (CHO) derived from C4 plants (maize, sugar cane), whereas a European diet contains primarily CHO derived from C3 plants (potato, sugar beet). The natural 13C enrichment of the first type of CHO is higher than that of the latter type. 13CO2 production from orally ingested C4 plant-derived CHO can, therefore, be used to quantify oxidation rates of orally ingested CHO at rest and during exercise. Recently it has been shown that oxidation rates assessed this way in North Americans should be corrected for an increase in breath background 13CO2 during exercise. We hypothesized that the indicated difference in metabolic origin of CHO would imply that no such correction is required for subjects on a European diet. We therefore studied changes from rest in breath 13CO2 enrichment in Dutch volunteers during cycle ergometry at 65% maximal work load (experiment 1, 2h, 6 subjects) and 70% maximal oxygen uptake (experiment 2, 90 min, 8 subjects) while ingesting water (experiments 1 and 2) and potato starch-derived glucose (experiment 2). Experiment 1 was done before and after careful instruction of the subjects to refrain from nutrient sources potentially containing CHO of C4 metabolic origin. No significant changes from rest 13CO2 enrichment were observed in tests with water and potato-derived glucose ingestion in subjects who excluded CHO of C4 metabolic origin from their diet.