L R Hackler’s research while affiliated with Cornell University and other places

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.

The apparent and true digestibilities of the same preparations of six proteins (spray dried whole egg, cottage cheese, canned tuna, peanut flour, soy isolate, and wheat gluten) were estimated in four to five men and in rats and compared to estimates of digestibility from three different in vitro enzymic digestion procedures. For all six proteins, the correlation coefficient was 0.46 between true digestibility in humans and in rats; with values for tuna excluded, r = 0.96. With all six proteins, none of the in vitro values was significantly correlated with values from humans or rats. However, with either the three animal proteins alone or the three plant proteins alone, correlations were high (r greater than 0.90) between one or more of the in vitro estimates and the observed true or apparent human and rat digestibilities. The differences in the relationship between enzymic digestion estimates and the human digestibility estimates for plant or animal proteins suggest that for accurate prediction of protein digestibility in humans by these enzymic methods, different equations would have to be used for plant and animal proteins. For protein sources containing both plant and animal protein, use of the in vitro enzymic procedures would give only an approximate estimate of digestibility in humans.

The intake of crude fiber in the American diet was assessed for 7 time periods between 1909 and 1975 using food consumption and composition tables. Crude fiber intake dropped 28% from 6.8 g/day in 1909 to 4.9 g/day in 1957 to 1959 and has remained at that level until the present. The intake of fiber from vegetables has remained relatively constant from 1909 to 1975 while potatoes, fruit, cereals, dry peas, and dry bean consumption have declined. The trends shown for crude fiber consumption in the United States support the hypothesis that fiber intake has decreased coincidentally with increases in degenerative diseases.

Published values on the water-holding capacities of various food sources of plant fiber were found to be incorrect. The proper calculation for estimating the water-holding capacity is shown. Corrected values for the water-holding capacity of these foods suggest that on a fresh weight basis, or as consumed, wheat bran is far superior to fruits and vegetables in holding water.