Fecal bulking effect of whole grain flour from selected grains

Cereal Chem. 68(5):556-558 In a four-week study, young rats were fed diets containing whole grain 22.6 (wheat-fed), 15.2 (oat-fed), 20.9 (rye-fed), or 44.9 (barley-fed) g for flour from wheat, oats, rye, or barley. At the 50% level used, these diets the four-week period. These weights were poorly correlated with SF intakes provided a total of 1.6, 3.0, 3.5, and 10.4 g of soluble fiber (SF) and but highly correlated with TDF (r = 0.97) and insoluble fiber (r = 1.00). 17.0, 10.6, 17.5, and 45.1 g of total dietary fiber (TDF), respectively. Fecal densities were significantly lower in rats fed celluloseor wheatTwo groups of rats were fed SF-free diets (cellulose-based) that provided based diets than in rats fed comparable (based on TDF intake) diets 10.5 or 44.9 g of TDF. Fecal dry weights in the grain-fed rats averaged based on the other three grains. A high fecal bulk, usually the consequence of a high fiber diet, is associated with a lower incidence of colon cancer (NCI 1985, Anderson 1986, Pilch 1987). Whole grain flours, because they contain more fiber than do the resultant refined flours, provide a greater fecal bulk than do refined flours. The content of fiber in whole grain flours is not the only factor that determines their fecal bulking capacity. Other factors, such as particle size, water-holding capacity, the presence of resistant starch, and the amount of soluble fiber (SF) they contain may also affect fecal bulk (Nyman and Asp 1982, Nyman 1985, Cadden 1986, Nyman et al 1986, Ranhotra et al 1991). SF is a significant component of total dietary fiber (TDF) in grains such as oats, barley, and rye. These grains are increasingly being incorporated into foods as a source of SF to lower elevated blood cholesterol, which is a risk factor in heart disease (Jenkins et al 1979). They undoubtedly also provide fecal bulk, but their relative capacity to do so is not well understood. The present study was undertaken to assess this capacity. Wheat, which is low in SF, and cellulose, which contains no SF, were used as control materials. Rats were used as the test model; they have been shown to respond in a manner similar to humans in this type of study (Nyman and Asp 1982, Nyman 1985, Nyman et al 1986). MATERIALS AND METHODS Test Samples All grains were ground (Wiley mill, model 4, Arthur H. Thomas Co., Philadelphia, PA) to pass through a 0.84-mm screen. The cellulose used as a control fiber source was obtained from a commercial source. Table I provides information on the composition of these samples. Diets Test samples were included in the diet at the 50% level (Table II). The two control (cellulose-based) diets represented the lower (4.6%) and the upper (19.6%) levels of TDF as encountered in the four grain-based diets. All diets were complete in nutrients required by rats (NRC 1987). Animals Six groups of male weanling rats (10 per group) of SpragueDawley strain (Harlan-Sprague-Dawley, Indianapolis, IN) were housed individually in suspended mesh-bottom stainless steel 'Presented at the AACC 76th Annual Meeting, Seattle, WA, October 1991. 2 Nutrition Research Group, American Institute of Baking, 1213 Bakers Way, Manhattan, KS 66502. 3 ConAgra Grain Processing Co., 1521 N. 16th St., Omaha, NE 681 10. @ 1991 American Association of Cereal Chemists, Inc. 556 CEREAL CHEMISTRY cages in a controlled environment. Sliding trays for fecal collection were provided under each cage. Each rat was allowed to consume an adequate, but the same (pair-fed), amount of total diet over the four-week test period; deionized water was offered ad libitum. Records of body weight were kept. Fecal Collection Feces were collected quantitatively (separately for each rat) throughout the four-week period, pooled, air-dried, and weighed, and their volumes were determined. Analyses The standard AACC methods (AACC 1983) were used to analyze test samples for protein (Kjeldahl), fat (acid hydrolysis), moisture, and ash. Fiber (TDF and SF) was determined by the enzymatic-gravimetric method of Prosky et al (1988). Fecal volume was determined in a long-stemmed, graduated cylinder, using fine sand as the embedding material. Density was calculated by dividing the fecal dry weights by volume. Statistical Analyses Mean comparisons were made with Duncan's multiple-range test using the Statistical Analysis System (SAS 1982). RESULTS AND DISCUSSION Diet and Fiber Intakes To eliminate the effect of ad libitum feeding on fecal bulk, all groups of rats were allowed to consume identical amounts of diets (Table III). These diets, however, differed in TDF and SF contents (Table II) and, as such, the intakes of TDF and SF varied greatly among groups of rats. Body Weight Gains All diets contained the same level of fat and protein (Table II). However, they differed in caloric density because the fiber levels differed; diets low in TDF and containing some SF promoted higher body weight gains in rats than diets devoid of SF or containing high levels of TDF. Fecal Weight Although a low fecal weight (or bulk) does not necessarily promote cancer, a high weight may protect against colon cancer (NCI 1985). Fecal weight is invariably higher in rats on fibercontaining diets than in those on fiber-free diets (Schneeman 1987, Ranhotra et al 1988). However, fiber-containing diets may differ in their potential to increase fecal weights even when they contain identical amounts of TDF. Such seems to be the case for sets of diets A and E and diets B and F. Diets A and B, in which cellulose was the fiber source, promoted significantly (P < 0.05) higher fecal dry weights than did the corresponding diets (diet E, oat-based, and diet F, barley-based). This may result from SF in oats and barley TABLE I Composition (%) of Test Samples Total Protein Dietary Soluble Sample Moisture (N X 5.7) Ash Fat Fiber Fibera Carbohydrates Celluloseb 3.8 . 0.2 0.2 95.8 . Whole grain flours Wheat 10.9 16.7 2.1 3.2 14.8 1.4 52.3 Rye 11.2 10.5 1.6 2.6 15.2 3.0 58.9 Oat 9.8 16.3 2.0 7.4 9.1 2.5 55.4 Barley 8.8 15.8 2.3 7.8 39.1 8.9 26.2 a Values were not used in calculating carbohydrate values. bAlphacel (ICN Biochemicals, Cleveland, OH). TABLE II Test Diets of Rats Diet