13C-Carbohydrate Breath Tests: Impact of Physical Activity on the Rate-Limiting Step in Lactose Utilization

Abstract

Background: ¹³CO₂ breath tests can be used to monitor carbohydrate digestion in the small intestine. However, after ingestion of ¹³C-substrates, ¹³CO₂ excretion in breath originates from two sources: a digestive/oxidative fraction, derived from the small intestine, and a fermentation fraction, derived from undigested substrate spill-over in the colon. In this study, the determinants of the digestive/oxidative fraction were analysed in order to improve the sensitivity/specificity of the ¹³C-carbohydrate breath tests. Methods: ¹³C-carbohydrate breath tests were performed in healthy adults using ¹³C-lactose, pre-digested ¹³C-lactose, ¹³C-glucose, and ¹³