Wheat bran ground to a coarse and fine particle size, purified cellulose and ethanol-extracted cabbage fiber, fed to 24 adult males during an 80-day metabolic trial, were examined for effects on intestinal transit time, laxation and stool composition. Brilliant blue, plastic pellets, polyethylene glycol (PEG)-4000 and Cr(III) mordanted onto isolated bran fiber were simultaneously administered for transit measurements. Intersubject variability in response to fiber source was highly significant for all transit and stool measurements. Only coarse bran or cellulose addition increased transit speed (decreased transit time) over basal rates. Grinding of bran significantly reduced fecal output because of reduced fecal water. Only subjects consuming cellulose or fine bran reported difficult or uncomfortable defecations. Though cabbage produced the smallest fecal output, stools had a high moisture content comparable to those obtained from coarse bran, which suggests a large microbial output in response to a fermentable substrate. Significant negative correlations were produced when changes in dry matter or cell wall intakes were regressed with Cr (III) transit. These findings suggest that the level of either food or fiber in the diet are variables that influence intestinal transit time and should be controlled in studies measuring it. Increases in fiber intake linearly increased fecal output of water and dry matter. Regression slopes were characteristic of each fiber source.

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A proposed approach to help address the fiher shortfall in the diets of Americans has been to increase intake of whole grains. The 2005 Dietary Guidelines for Americans recommended for the first time that all age groups consume at least half their grain servings as whole grains as 1 way to help achieve fiher recommendations. Yet the amount of fiher in products promoting their whole-grain content can vary suhstantially. Differences in the nutrient composition of whole-grain sources, variations in the amount of whole grain used in prepared products, and limitations in current whole-grain lahel statements all contribute to broad disparities in the fiber content. Current MyPlate meal patterns recommend whole-grain consumption at a level providing about one-quarter to one-third of daily fiber needs. To help close the fiher gap, we must educate consumers on how to find whole-grain foods that provide at least a good source of fiber as well as encourage the intake of any grain food that provides fiber. This is particularly important given the role of fiber in whole-grain health benefits. Nutr Today. 2011;46(6).293-298