B.A. Lewis’s research while affiliated with Cornell University and other places

There is a need to standardize the NDF procedure. Procedures have varied because of the use of different amylases in attempts to remove starch interference. The original Bacillus subtilis enzyme Type IIIA (XIA) no longer is available and has been replaced by a less effective enzyme. For fiber work, a new enzyme has received AOAC approval and is rapidly displacing other amylases in analytical work. This enzyme is available from Sigma (Number A3306; Sigma Chemical Co., St. Louis, MO). The original publications for NDF and ADF (43, 53) and the Agricultural Handbook 379 (14) are obsolete and of historical interest only. Up to date procedures should be followed. Triethylene glycol has replaced 2-ethoxyethanol because of reported toxicity. Considerable development in regard to fiber methods has occurred over the past 5 yr because of a redefinition of dietary fiber for man and monogastric animals that includes lignin and all polysaccharides resistant to mammalian digestive enzymes. In addition to NDF, new improved methods for total dietary fiber and nonstarch polysaccharides including pectin and beta-glucans now are available. The latter are also of interest in rumen fermentation. Unlike starch, their fermentations are like that of cellulose but faster and yield no lactic acid. Physical and biological properties of carbohydrate fractions are more important than their intrinsic composition.

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.

The effect of particle size of dietary wheat bran on human colonic function was studied in young adult men. Controlled, low-fiber diets supplemented with 32 g of either coarse or finely ground bran were served daily in a metabolic unit. Measurements of the mean transit time were made using polyethylene glycol and barium impregnated radioopaque pellets. In subjects receiving equal levels of both bran diets, coarse bran produced significantly (P = 0.95) shorter mean transit time than did finely ground bran. Values of mean transit time for coarse bran were 42.3 hr (polyethylene glycol) and 37.4 hr (pellets) while 57.9 hr (polyethylene glycol) and 56.5 hr (pellets) were found for fine bran. Daily fecal wet and dry weights from the coarse bran diet were found to be significantly greater by 14% (P = 0.99) and 7% (P = 0.95) than the weights found during the ingestion of finely ground bran. The moisture content of feces from subjects receiving the coarse bran diet was 75.2%, significantly higher (P = 0.99) than the value of 72.3% found with fine bran. No significant differences in the number of defecations per day were noted. Mean digestibilities for hemicellulose was 50% for coarse bran and 54% for fine bran. Cellulose digestibility was 6% in the coarse bran diet and 23% in the fine bran. While significant differences (P = 0.95) in digestibilities between the two brans were not shown, mean digestibilities were greater for fine bran components. Results from this study indicate that finely ground wheat bran is less effective than coarse bran in holding water in the feces and in promoting rapid transit of digesta through the gut. These findings suggest that coarse bran and food products fortified with coarsely ground bran should be the choice of patients with diverticular disease and of people desiring a high fiber diet to promote colonic health. Am. J. Clin. Nutr. 33: 1734-1744, 1980.