Evaluation of 13CO2 breath tests for the detection of fructose malabsorption

Breath hydrogen (H2) studies have made clear that small intestinal absorption of fructose is limited, especially in toddlers. Malabsorption of fructose may be a cause of recurrent abdominal pain and chronic nonspecific diarrhea (toddler's diarrhea). Fructose absorption is facilitated by equimolar doses of glucose and, as we have found, amino acids (especially L-alanine); the mechanism underlying this effect remains unclear. To study fructose absorption in a more direct way, we combined breath H2 studies with breath 13CO2 studies. Gastric emptying was studied by using L-glycine-1-13C in 4 children from 12.1 to 16.0 years of age. After 25 gm of fructose and 27.5 gm of glucose, when given together, gastric emptying was significantly (p or = 20 ppm, and the addition of glucose or L-alanine resulted in significantly lower breath H2 increases (p < or = 0.005 for glucose, p < or = 0.001 for alanine). In contrast, the addition of alanine or glucose did not change the pattern of breath 13CO2 excretion in the 5 older children, whereas in the 4 younger children (with relatively higher doses), L-alanine addition resulted in significantly lower increases in breath 13CO2. In the latter group, for each time point, breath H2 and 13CO2 concentrations after fructose were compared with those after fructose plus L-alanine; in 20 out of 24 points, both H2 and 13CO2 were higher after fructose. These results suggest that 13CO2 not only originated from the oxidation of absorbed substrate but also, at least in part, from colonic bacterial metabolism. For the detection of [correction of or] fructose malabsorption--as opposed to, for instance, lactose--the 13CO2 breath test seems to be of limited value.