Removing lactose from milk does not delay bowel function or harden stool consistency in lactose-tolerant women

To investigate whether removing lactose from milk delays bowel function in lactose-tolerant women. We also examined how well the participants' subjective evaluation of the stool consistency according to the Bristol Stool Form Scale correlated with values obtained by dry matter analysis and penetrometry.

A randomized double-blind cross-over trial. Thirty-three lactose-tolerant women consumed, in random order, 800 ml of lactose-free or ordinary milk per day for 2 weeks, with their main meal, but otherwise followed a lactose-free diet. The subjects estimated stool consistency according to the Bristol Stool Form Scale, registered stool frequency and gastrointestinal symptoms and collected stool samples.

The mean intake of lactose was 3.5 and 38.4 g/day during the lactose-free and the ordinary milk periods, respectively. There were no statistically significant differences between the lactose-free and the ordinary milk periods in stool frequency, gastrointestinal symptoms, stool hardness or faecal dry matter. Faecal pH was lower during the lactose-free milk period than in the ordinary milk period. The subjective estimation of stool hardness correlated well with the values obtained by dry matter analysis and penetrometry.

Lactose-free milk does not delay bowel function in lactose-tolerant women. The Bristol Stool Form Scale is a useful method of evaluating stool hardness.