Urine and stool measures of adherence to a dietary wheat bran supplement

Development of a reliable marker of adherence to high fiber diets is essential for accurately assessing fiber intakes in community interventions or clinical trials. To date, these estimates have used primarily either stool weights or dietary methods. Stool measures require 3-3 day collections to obtain valid estimates due to large day-to-day variation in stool size and frequency. Dietary measures can be biased in studies that promote higher fiber intakes. Our wheat bran intervention study collected blood, 24-hr urine and 3 day stool samples from 45-65 year old, predominately Black, lower SES, Southern men and women before and up to 6 weeks after a daily supplement of 1/2 cup of wheat bran cereal (13.5 g fiber) spiked with 50 mg of riboflavin (biomarker of supplement intake). This supplemental dose was shown to correlate with urinary riboflavin excretion (r= 0.96, p< 0.001). Pre and post measures (mean ±se) were 2.9 ±0.9 vs. 10.7 ±2.4 mg/day riboflavin (n=8), 129 ±14 vs. 163 ±20 g/day stool wet wt. and 32 ± 3 vs. 39 ±4 g/day stool dry wt (n=7). Comparison of the difference between pre and post measures showed significant increases in riboflavin (p=0.016) and increased stool measures that were not significant. These results indicate that riboflavin is the more feasible biomarker of fiber intake in a community study and exhibits greater change in mean values than stool measures.