Absorption of Short-Chain Fatty Acids from the Human Colon Measured by the¹⁴Co₂Breath Test

The absorption and metabolism of short-chain fatty acids (SCFAs) have been studied in 31 patients. Physiological amounts (7.5 mmol) of (1-14C)-labeled acetic, propionic, and butyric acid and (2-14C)-labeled propionic acid were instilled into the cecum and ascending part of the colon during colonoscopy, and the metabolism of acids to CO2 was measured for 24 h by the 14CO2 breath test. During the first 6 h the cumulative output of 14CO2 from the (1-14C)-labeled acetic, propionic, and butyric acids were (median and range) 50% (46%-56%), 50% (43%-56%), and 63% (58%-73%) and during 24 h 55% (50%-63%), 58% (46%-60%), and 70% (63%-83%), respectively, of the instilled dose. The elimination patterns of the (1-14C)-labeled acids were rather similar, although butyric acid was eliminated to a somewhat greater extent than acetic and propionic acid (p less than or equal to 0.01). (2-14C)-labeled propionic acid was eliminated more slowly than (1-14C)-labeled propionic acid, with a cumulative output of 37% (30%-39%) after 6 h (p less than 0.01), but reached the same value after 24 h, 54% (47%-60%). In agreement with findings in other species, humans have a great capacity for uptake and metabolism of SCFAs formed in the colon.