The longterm goal of the proposed research is to elucidate the mechanisms of action of dietary fiber. Some are a consequence of its presence in the gut; others are undoubtedly a result of its metabolism, which occurs principally in the large bowel through the action of microflora. Microbial activity will, however, depend upon the substrates available. The effects of fiber on small bowel digestive enzyme activities, the viscosity of the lumenal contents, the rate of transit and mucin secretion all influence the substrate available for fermentation. The primary aim of this application is to study the nature and extent of metabolism of dietary fiber and other substrates in the gastrointestinal tract and begin to examine the distribution of the energy released from these substrates between bacteria and short chain fatty acids. Methods to characterize dietary fiber and to distinguish it from other polysaccharide sources in gut lumenal contents, i.e. bacteria, mucins and undigested food carbohydrate, are a major focus of our research. These methods will be used to determine the metabolism of dietary fiber by analyzing digesta collected from conscious minipigs with cannulas surgically implanted at different sites in the gastrointestinal tract. The proportion of substrate used for bacterial growth and metabolism will be evaluated by measuring bacterial mass and disappearance of digesta. Energy available for absorption will be assessed by measuring short chain fatty acids produced during in vitro incubation of digesta. We hypothesize that soluble fibers and mucin will be rapidly fermented in the proximal colon and that insoluble fiber will be metabolized principally in the distal colon. This study will address several significant human health issues, including the role of adequate dietary fiber in the treatment of obesity and diabetes mellitus and in the process of atherogenesis. This research also will test the hypothesis that fiber affects colon carcinogenesis by modifying microbial metabolism, in part, by altering the substrate available for fermentation.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK021712-11
Application #
3227092
Study Section
Nutrition Study Section (NTN)
Project Start
1983-12-01
Project End
1991-07-31
Budget Start
1990-02-01
Budget End
1991-07-31
Support Year
11
Fiscal Year
1990
Total Cost
Indirect Cost
Name
University of Wisconsin Madison
Department
Type
Schools of Earth Sciences/Natur
DUNS #
161202122
City
Madison
State
WI
Country
United States
Zip Code
53715
Marlett, J A; Marlett, J A (2000) Changes in content and composition of dietary fiber in yellow onions and red delicious apples during commercial storage. J AOAC Int 83:992-6
Monsma, D J; Thorsen, P T; Vollendorf, N W et al. (2000) In vitro fermentation of swine ileal digesta containing oat bran dietary fiber by rat cecal inocula adapted to the test fiber increases propionate production but fermentation of wheat bran ileal digesta does not produce more butyrate. J Nutr 130:585-93
Chen, H L; Haack, V S; Janecky, C W et al. (1998) Mechanisms by which wheat bran and oat bran increase stool weight in humans. Am J Clin Nutr 68:711-9
Monsma, D J; Marlett, J A (1996) Fermentation of carbohydrate in rat ileal excreta is enhanced with cecal inocula compared with fecal inocula. J Nutr 126:554-63
Monsma, D J; Marlett, J A (1995) Rat cecal inocula produce different patterns of short-chain fatty acids than fecal inocula in in vitro fermentations. J Nutr 125:2463-70
Cabotaje, L M; Shinnick, F L; Lopez-Guisa, J M et al. (1994) Mucin secretion in germfree rats fed fiber-free and psyllium diets and bacterial mass and carbohydrate fermentation after colonization. Appl Environ Microbiol 60:1302-7
Monsma, D J; Vollendorf, N W; Marlett, J A (1992) Determination of fermentable carbohydrate from the upper gastrointestinal tract by using colectomized rats. Appl Environ Microbiol 58:3330-6
Hildebrandt, L A; Marlett, J A (1991) Starch bioavailability in the upper gastrointestinal tract of colectomized rats. J Nutr 121:679-86
Cabotaje, L M; Lopez-Guisa, J M; Shinnick, F L et al. (1990) Neutral sugar composition and gravimetric yield of plant and bacterial fractions of feces. Appl Environ Microbiol 56:1786-92
Liebl, B H; Fischer, M H; Van Calcar, S C et al. (1990) Dietary fiber and long-term large bowel response in enterally nourished nonambulatory profoundly retarded youth. JPEN J Parenter Enteral Nutr 14:371-5

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