Article Text
Statistics from Altmetric.com
There is no easy and reliable test universally accepted in clinical practice to measure fat digestion. Fat balance studies are insensitive and unpleasant for regular clinical assessment, direct measures of pancreatic function are impractical for repeated use, the “steatocrit” method is not quantitative; tubeless tests have not proved to be effective substitutes; and clinical measures, such as stool frequency, appearance, and consistency, are subjective.
In 1981 an isotope breath test named the “mixed triglyceride (MTG) breath test” was described by Ghoos et al to measure intraduodenal lipase activity as an index of exocrine pancreatic function in adults.1 It was later modified by the substitution of 13C for 14C.2 The labelled carbon, originating from the labelled fat as a result of digestion, absorption, and oxidation, can be detected in exhaled carbon dioxide and the amount recovered in the breath is an indirect measure of lipolysis within the small intestine. The MTG breath test derives its name from the presence in the test molecule of both long and medium chain fatty acids. The labelled substrate consists of a triglyceride with two molecules of stearic acid at the Sn-1 and three positions and 13C octanoic acid in the Sn-2 position (1,3-distearyl [13C octanoyl] glycerol).
The MTG has a number of advantages over other triglycerides, such as trioctanoin and triolein,3 which have been used as substrates with which to measure fat digestion in adults and children.4 ,5 Although the MTG is not representative of a naturally occurring dietary fat, the rate limiting step in its digestion is hydrolysis of the two stearyl groups by pancreatic lipase. Normal diet contains little octanoate, and the labelled tracer is not therefore diluted by unlabelled substrate. Octanoic acid, as a medium chain fatty acid, is rapidly and completely …