Colonic fermentation of complex dietary carbohydrates in short-bowel patients. No association with hydrogen excretion and fecal and plasma short-chain fatty acids.

Abstract

The colonic degradation of carbohydrates (fermentation) to short-chain fatty acids (SCFAs) appears to have major impacts on colonocyte function, sodium and water absorption, and large-bowel energy salvation, but how to quantify the in vivo fermentation in man is still debatable. Indicators of colonic fermentation, fecal and plasma SCFAs and breath hydrogen (H2), were measured in 10 short-bowel patients (mean +/- SE; 106 +/- 21 cm) with totally preserved large bowels who were on a 60% high-carbohydrate, 20% low-fat diet, compared with the reversed isocaloric 20% low-carbohydrate, 60% high-fat diet. This human model showed large differences in large-bowel fermentation, as excretions of calories were reduced (40%; 485 +/- 151 kcal/day) and excretions of carbohydrates were unchanged and low with the high-carbohydrate diet as compared with the low-carbohydrate diet, in contrast to unchanged calorie excretion in short-bowel patients with no colonic function. Fecal concentrations of SCFAs did not change when the diet was changed from the high content to the low content of carbohydrates (82 +/- 11 mmol/l and 79 +/- 9 mmol/l, respectively). The ratio of acetate in feces increased (from 48 +/- 4% to 54 +/- 3%; p = 0.01) on the high-carbohydrate diet, whereas the percentage of the other SCFAs decreased proportionally. Plasma SCFAs 2 h and 6 h after breakfast were also identical when comparing the two dietary regimens. Nor were the peak H2 breath excretion and the area under the H2 excretion-versus-time curve increased by the threefold increase in the intake of dietary carbohydrates. Fecal and plasma SCFAs and breath H2 excretion are of limited value in the evaluation of even large differences in colonic fermentation of complex dietary carbohydrates.