Measurement of starch absorption in humans

Although starch provides a large fraction of human caloric intake, there is limited information concerning the efficiency of intestinal absorption of this nutrient. Owing to the fermentation of starch by colonic bacteria, there is no quantitative test for starch absorption comparable to the fecal fat determination. The most accurate estimation of starch absorption has been obtained by intubating the terminal ileum and aspirating ileal contents following ingestion of a meal containing starch plus a nonabsorbable marker. Starch absorption is calculated from the ratio of starch:marker in the ileal aspirate relative to the ratio in the meal. Disadvantages of the technique are the requirement for ileal intubation and the possible adverse effect of intubation on the absorptive process. A more widely used technique to assess starch absorption involves measurement of breath hydrogen (H₂) excretion after ingestion of starch. Malabsorbed starch is fermented by colonic bacteria with liberation of H₂ that is absorbed and excreted in expired air. This test is simple and noninvasive and can provide quantitative measurements of starch malabsorption. Application of this technique has demonstrated that 5-10% of starch in wheat, potatoes, and corn is not absorbed by healthy subjects, while rice starch is nearly completely absorbed.