Diet and Health Implications for Reducing Chronic Disease Risk (1989) / Chapter Skim
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10 Dietary Fiber
10 Dietary Fiber
Pages 291-310
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From page 291... ...
first defined dietary fiber as components of the plant cell wall that resist digestion by secretions of the human alimentary tract. These include cellulose, hemicelluloses, pectin, and lignin.
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From page 292... ...
High fiber intakes promote increased bacterial mass but do not alter the microflora composition (Baird et al., 1977; Drasar et al., 1976; Finegold and Sutter, 1978~. Colonic bacteria attack fermentable fiber components and degrade at least a portion of them to short-chain fatty acids and gases.
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From page 293... ...
293 PATTERNS OF FIBER INTAKE IN THE UNITED STATES The paucity of accurate population-based data on fiber intake, due largely to the lack of data on fiber in foods, hinders interpretation of epidemio~ logic studies of the relationship of dietary fiber to chronic diseases. In addition, many of these studies used only crude fiber data.
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From page 294... ...
EVIDENCE ASSOCIATING DIETARY FIBER WITH CHRONIC DISEASES Hyperlipidemia and Coronary Heart Disease Epidemiologic Studies The effects of dietary fiber on lipid metabolism in humans have been described in several comprehensive reviews (Judd and Truswell, 1985; Kay and Truswell, 1980; Story, 1980; Vahouny, 1982, 1985~. Most epidemiologic data on fiber intake and levels of serum lipid, lipoprotein, and apolipoprotein come from comparisons of vegetarian and nonvegetarian populations.
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From page 295... ...
(1980) showed that serum cholesterol levels were inversely associated with fiber intake, but this association no longer held when caloric intake was taken into account in the analysis.
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From page 296... ...
In a later study of 38 countries, intemational age-standardized colon cancer rates did not corre~ate with fiber intake after controlling for intake of fat. However, there was a negative correlation of cereal intake with colon cancer, even after contro}ling for fat intake (McKeown-Eyssen and Bright-See, 19841.
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From page 297... ...
In these studies, total fiber intake was estimated from diet history questionnaires administered to populations consuming diets similar to average diets in the United States. One of these, in Canada, showed no association between colorectal cancer and crude fiber intake or total dietary fiber (lain en al., 1980; Miller en al., 1983~.
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From page 298... ...
Addition of IS% wheat bran inhib' ited both AOM - and MN U- induced colon carcinogenesis. In another study, the same substitution protected against oral and subcutaneous DMH-induced colon cancer (Barbolt and Abraham, 19781.
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From page 299... ...
Clinical and Metabolic Studies Although clinical and metabolic studies indicate that some fiber supplements can control glycemic response in diabetics, the relevance of these studies to the prevention of diabetes is unknown. In general, these studies indicate that water-soluble fibers such as guar and pectin are most effective in reducing the postprandial rise in serum glucose after mixed meals or glucose load than are waterinsoluble fibers such as wheat, corn bran, soy hulls, and cellulose (Ienkins et al., 1976, 1978b, 1979a; LSRO, 1987; Monnier et al., 1978; Morgan et a!
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From page 300... ...
OTHER CHRONIC DISEASES Hypertension Epidemiologic studies have demonstrated lower mean blood pressures in vegetarians and other groups consuming diets high in fiber than in nonvegetarians and other groups consuming diets lower in fiber (Armstrong et al., 1977; Rouse et al., 1982; Sacks et al., 1974; Trowell, 1981~. Similarly, clinical studies indicate a fairly consistent blood pressure-lowering effect of diets with high levels of fiber from various sources in normal as well as hypertensive subjects (Anderson, 1986; Dodson et al., 1984; Lindah!
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From page 301... ...
He concluded that there is little evidence that high-fiber diets alone induce a mineral deficiency in people who otherwise consume a balanced diet. OTHER POTENTIAL EFFECTS Sudden shifts from low-fiber to high-fiber diets, particularly those with increased intakes of wheat bran and guar gum, can produce undesirable gastrointestinal symptoms, including bloating, nausea, increased flatulence, eructation, and vomiting as well as steatorrhea in patients with pancreatic insufficiency (Dutta and HIasko, 1985; LSRO, 1987~; however, these effects seem to be temporary.
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From page 302... ...
The general lack of data on dietary levels of specific fiber fractions may also have contributed to the inconsistency in study findings. Total Dietary Fiber Metabolic and epidemiologic studies indicate that the excretion of fecal mutagens is more prevalent and the concentration of fecal secondary bile acids higher in populations at high risk of colon cancer than in those at low risk.
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From page 303... ...
DIRECTIONS FOR RESEARCH The committee recommends that the following types of research be undertaken: · More definitive analytical epidemiologic studies that are designed carefully to include adequate variation of dietary fiber intake in the study pops Cation; improved methods for assessing dietary intake in general; improved quality and quantity of data about specific fractions of fiber consumed by the study population; adequate sample size; and collaboration among investigators to adopt a common protocol and method of dietary assessment so that any inconsistencies in results can be related to differences in populations. · Intervention studies in human populations that could serve tO cIari*
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From page 304... ...
1983. The effect of pectin and wheat bran on platelet function and haemostasis in man.
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From page 305... ...
1983. Enhancement of rat colon carcinogenesis by wheat bran consumption during the stage of 1,2-dimethylhydrazine administration.
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From page 306... ...
1975. Low-fiber intake as an etiologic factor in cancer of the colon.
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From page 307... ...
1985. The effect of guar gum and fiber-enriched wheat bran on gastric emptying of a semisolid meal in healthy subjects.
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From page 308... ...
1985. Trace elements in serum and urine of diabetic patients given bread enriched with wheat bran or guar gum.
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From page 309... ...
1979. Effect of dietary alfalfa, pectin, and wheat bran on azoxymethane- or methylnitrosourea-induced colon carcinogenesis in F344 rats.
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