Clausen M R, Jørgensen J, Mortensen P B
Department of Medicine CA 2121, The Rigshospital, University of Copenhagen, Denmark.
Dig Dis Sci. 1998 Dec;43(12):2696-707. doi: 10.1023/a:1026659512786.
Whether carbohydrate malabsorption causes diarrhea probably depends on the balance between the osmotic force of the carbohydrate and the compensatory capacity of the colon to dispose of the carbohydrate by bacterial fermentation. The present study evaluated the specific role of the osmolarity by comparing the severity of diarrhea after ingestion of two nonabsorbable carbohydrates, the fructooligosaccharide Idolax and the disaccharide lactulose. Both carbohydrates are readily fermented by the colonic flora but differ in osmolarity, the osmotic force being twice as high for lactulose as for Idolax. Twelve subjects were given increasing doses (0, 20, 40, 80, 160 g/d) of Idolax and lactulose in a crossover design. Every dose level was administered for three days with intervals of one week. Stools were collected on the third day to determine 24-hr volume, concentrations of short-chain fatty acids, L- and D-lactate, residues of Idolax or lactulose, sodium, potassium, pH, osmolarity, and in vitro productions of organic acids. Measured by short-chain fatty acid and lactate formation in a fecal incubation system, the fermentation of Idolax and lactulose was identical and very rapid compared with a range of reference carbohydrates. A laxative effect of both Idolax and lactulose was demonstrated. The increment in fecal volume as a function of the dose administered was twice as high for lactulose (slope of the regression line = 7.3, r = 0.64, P< 10(-5)) as for Idolax (slope = 3.7, r = 0.51, P<10(-3)), i.e., isosmolar doses of lactulose and Idolax had the same effect on fecal volume. The variation in fecal volume was substantial (lactulose 80 g/day: 110-1360 g/day; Idolax 160 g/day: 130-1440 g/day). High responders had earlier and larger fecal excretions of the saccharide compared with low-responders. Fecal volume in carbohydrate-induced diarrhea is proportional to the osmotic force of the malabsorbed saccharide, even though all or the majority of the saccharide is degraded by colonic bacteria. The capacity to modify the diarrhea varies considerably from person to person and is associated with colonic saccharide disposal, whereas the variation in response to isosmolar amounts of different saccharides is small within the same individual.
碳水化合物吸收不良是否会导致腹泻可能取决于碳水化合物的渗透力与结肠通过细菌发酵处理碳水化合物的代偿能力之间的平衡。本研究通过比较摄入两种不可吸收碳水化合物（低聚果糖Idolax和二糖乳果糖）后腹泻的严重程度，评估了渗透压的具体作用。这两种碳水化合物都很容易被结肠菌群发酵，但渗透压不同，乳果糖的渗透力是Idolax的两倍。12名受试者采用交叉设计，给予递增剂量（0、20、40、80、160 g/天）的Idolax和乳果糖。每个剂量水平给药三天，间隔一周。在第三天收集粪便，以测定24小时粪便量、短链脂肪酸、L-和D-乳酸的浓度、Idolax或乳果糖的残留量、钠、钾、pH值、渗透压以及体外有机酸的产生量。通过粪便培养系统中短链脂肪酸和乳酸的形成来衡量，与一系列参考碳水化合物相比，Idolax和乳果糖的发酵情况相同且非常迅速。已证实Idolax和乳果糖都有轻泻作用。乳果糖导致的粪便量增加与给药剂量的函数关系（回归线斜率 = 7.3，r = 0.64，P < 10(-5)）是Idolax（斜率 = 3.7，r = 0.51，P < 10(-3)）的两倍，即等渗剂量的乳果糖和Idolax对粪便量的影响相同。粪便量的变化很大（乳果糖80 g/天：110 - 1360 g/天；Idolax 160 g/天：130 - 1440 g/天）。与低反应者相比，高反应者的糖类粪便排泄更早且更多。碳水化合物诱导的腹泻中粪便量与吸收不良糖类的渗透力成正比，即使所有或大部分糖类被结肠细菌降解。改变腹泻的能力因人而异，且与结肠糖类处理有关，而同一人对等渗量不同糖类的反应差异较小。
