special

article

Gene A. Spiller2

and

Ruth

M. Kay3

Dietary fiber is a complex group of polymers with differing physical and chemical characteristics. The tendency to oversimplification has led many investigators to generalize concerning nomenclature and effects. With the cooperation of chemists, biochemists, nutritionists, and clinicians, a systematic approach to the study of dietary fiber is now possible. The participants in the dietary fiber workshop at the XI International Congress of Nutrition agreed that certain physiological effects of fiber are today fairly well established. These effects are, however, specific for different physicochemical forms of fiber and extreme care needs to be used in defining the type of polymer used in any study. It appears important to summarize the conclusions and recommendations of this International Congress in an area of nutrition where much confusion still exists regarding chemistry, terminology, and the relationship of physicochemical properties to physiological action. The conclusions and recommendations developed by the workshop are as follows. Definition

and

chemistry

1) There is no doubt that both the water insoluble and the water soluble carbohydrate polymers that are not digested by human digestive enzymes should be included in the overall definition of fiber. 2) Crude fiber bears no consistent quantitative relationship to dietary fiber and use of this procedure should be abandoned. 3) The neutral detergent (NDF) method is 2102

The American

Journal

of Clinical

Nutrition

acceptable for the routine determination of insoluble fiber. In foods containing starch, it must be preceded by hydrolysis of the amylose fraction. 4) Determination of water soluble components (gums, mucilages, pectic substances) must constitute part of any routine method. Dialysis or organic solvent precipitation methods are acceptable. 5) Enzymatic methods may have widespread applicability since they enable fractionation and analysis of major fiber cornponents including water soluble materials. 6) Although rapid quantitative methodologies are acceptable for routine use such as industry quality control, the more tedious qualitative methods are essential in defining the chemical characteristics of specific fibers with known physiological effects. 7) Defined standards should be made available for quality control and for further characterization of physicochemical properties. Standards should include defined fiber isolates (cellulose, lignins, pectins) as well as chemically characterized native food sources. 8) There is a specific requirement for concise information on the physicochemical properties of different fibers since these may determine physiological effects. Of particular importance are solubility, density, particle ‘The workshop was composed of Gene A. Spiller (USA), chairperson, N. G. Asp (Sweden), R. M. Kay (Canada), B. F. Harland (USA), B. Modan (Israel), D. Schaller (USA), D. A. T. Southgate (UK), 0. Theander (Sweden), and G. Vahouny (USA). 2 Principal Scientist, Syntex Research, Palo Alto, California. Assistant Professor, University of Toronto, Toronto, Canada.

32: OCTOBER

1979, pp. 2102-2103.

Printed

in U.S.A.

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Recommendations and conclusions of the dietary fiber workshop of the Xl International Congress of Nutrition, Rio de Janeiro, 19781

DIETARY

FIBER

Gut

function

and

pathology

1) Fiber has an established role in the normalization of whole gut transit, stool bulk and consistency, and prevention and treatment of constipation. More information is required on the efficacy of food fibers other than cereal bran. 2) Some stool bulking fibers reduce intraluminal pressure, muscular hypertrophy and associated symptoms in diverticular disease; these fibers have an important role in the treatment of uncomplicated forms of the disease. 3) Further studies are required on the effect of fibers on chemically-induced carcinogenesis in animals and on the mechanism of this effect. Attention should be directed toward effects on colonic pH and redox conditions, intestinal flora and its metabolic activity, and on concentrations of bile acids and other possible procarcinogens. 4) More information is required on the effect of different fibers on lower gut morphology and on the significance of these effects.

Cholesterol

and

bile

acid

metabolism

1) Different types of dietary fiber differ considerably in their effects on plasma lipids and steroid excretion. Further studies are required to determine the qualitative effects on plasma lipids and lipoproteins, of various food fibers as eaten. 2) The mechanism of the hypocholesterolemic effect of mucilaginous fibers (i.e., pectin

2103

and guar) is not clear; it is unlikely to be due solely to an increase in fecal steroid loss. Colonic absorption of short chain fatty acid and sterol metabolites may affect hepatic cholesterolgenesis. Certain fibers also alter blood levels oflipid active hormones such as insulin. 3) There is a specific requirement for information on the effects of different fibers on the site and route of fat absorption and on chylomicron formation. 4) Studies are required to further quantitate the effects of different fibers on the bacterial modification of colonic sterols, on fecal steroid losses, biliary bile acid and lipid composition, and on mouth to ileum transit time and bile acid pool size. Carbohydrate

absorption

and

metabolism

1) Dietary fibers modify glucose absorption and may be of clinical usefulness in the prevention and treatment of adult-onset diabetes mellitus, hypoglycemia, and obesity. 2) Information is required on the effects of fibers on the site of glucose absorption and on the release of gastrointestinal hormones affecting glucose metabolism. 3) Mucilaginous fibers slow upper intestinal transit time. Clinical studies are required to determine the possible usefulness of these materials in pathological disorders of the small intestine. 4) There are suggestions that fiber may have a prolonged effect on glucose tolerance. Information should be obtained on the changes in small intestinal morphology secondary to chronic fiber ingestion. 5) Clinical trials are required to determine the value of food-derived fiber in diabetic management. It was the consensus of the meeting that although considerable refmement can be expected in our understanding of the mode of action of various fibers on a number of physiological processes, dietary fiber has certain established homeostatic and therapeutic roles in human nutrition.

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surface area, hydration capacity, cation exchange properties, organic adsorption characteristics, and susceptibility to colonic degradation. 9) The effects of the fiber polymer per se should not be confused with the possible effects of associated substances (e.g., phytates on intestinal absorption of certain minerals). size,

WORKSHOP

Recommendations and conclusions of the dietary fiber workshop of the XI International Congress of Nutrition, Rio de Janeiro, 1978.

special article Gene A. Spiller2 and Ruth M. Kay3 Dietary fiber is a complex group of polymers with differing physical and chemical characterist...
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