High-fiber rye bread improves bowel function in postmenopausal women but does not cause other putatively positive changes in the metabolic activity of intestinal microbiota

We have reported previously that rye bread (RB) as a part of the conventional diet affects bowel function and the metabolic activity of the microbiota differently in men and women. Because a higher intake of fiber by men could explain the difference in response, in the present randomized crossover trial, we studied the effects of a RB with increased fiber content vs white wheat bread (WB) in 39 postmenopausal women aged 59 ± 6 years (mean ± SD). The women consumed RB and WB for 8 weeks in random order. The composition of fecal microbiota; activities of bacterial β-glucosidase, β-glucuronidase, and urease; and concentration of short-chain fatty acids in feces, concentration of plasma enterolactone, fecal frequency, and consistency were determined. Mean intakes of dietary fiber were 47 ± 9 and 15 ± 4 g during the RB and WB periods, respectively. Rye bread significantly increased fecal frequency and produced softer stools, and increased the concentration of plasma enterolactone and the activities of β-glucosidase and urease as compared with WB (P < .05). There were no differences in the composition of the fecal microbiota, the activity of β-glucuronidase, and the concentration of short-chain fatty acids in feces between the test bread periods. This study shows that RB in comparison to WB improves bowel function and increases the concentration of plasma enterolactone in postmenopausal women, thus improving bowel health. However, lack of other putatively positive changes observed previously in men consuming RB indicates possible sex differences in the response of colonic microbiota to dietary fiber.