Abstract: Methods of measuring gastric emptying time comprising providing to a patient a meal comprising a breath test food additive substrate, wherein the substrate is a linear or cyclic acyl aminoacid peptidomimetic that includes a radioactive or non-radioactively labeled carbon atom; having the patient digest the meal so that the carbon labeled nutrients therein are absorbed in the small intestine and metabolized to labeled CO2; and, at periodic intervals, detecting the level of labeled CO2 in breath samples taken from the patient to determine the rate of gastric emptying are disclosed.