Before making DF recommendations, the physiological effects of its different g components must be known. The two main types of DF, water-soluble (SDF) j and water-insoluble (IDF), have some different mechanisms of action in vivo. t?
The SDF such as soluble P-glucans, pectins, gums, mucilages, and some hemicel- ^
luloses delay transit time in the gut, delay gastric emptying, impede the absorption of certain nutrients like glucose, and decrease serum cholesterol levels (26). Insol- |
uble DF like cellulose, lignin, and other hemicelluloses increase intestinal transit time and fecal weight, slow starch hydrolysis, and delay glucose absorption (26). Appropriate amounts of both types of fiber are important for overall health.
The health beneficial effects of a dietary recommendation should also outweigh potential deleterious consequences. Using the estimation that 35% of all cancer cases are attributable to diet, 315,000 new cancer cases or 166,000 cancer
Cho et al.
deaths would result in the United States if dietary goals for cancer prevention such as increasing DF intake levels are not achieved (27). This could cost as much as $25 billion a year. Based on international correlation statistics, an inverse relationship has been found between fiber and fiber-containing foods and colon cancer risk (28, 29). After examination of all fiber sources, the Life Science Research Office (LSRO) (30) determined that the IDF-rich wheat bran most consistently reduced colon tumor incidence in animal models. Recurrence of precan-cerous polyp lesions in the rectum has also been shown to be lower with wheat bran in humans (31). Both IDF and SDF may reduce breast cancer risk by binding estrogen, a potent promoter, and thus preventing enterohepatic reabsorption and lowering circulating levels (32). Although increased DF intake seems to be beneficial in terms of cancer, there are concerns about impaired mineral availability. Examination of populations that consume much higher levels of DF (e.g. vegetarians vs. omnivores) showed that mineral levels in various biological samples were comparable to those with lower DF intakes (30). In addition, bone mineral mass was observed to be higher or at least the same. Thus, bioavailability of minerals with higher DF intakes does not appear to be an issue as long as intakes are adequate.
Other issues that are considered in making a recommendation are the intended audience, the current intake levels of DF, and how the DF will be consumed (i.e. in foods vs. supplements) (30). Recommendations are generally based on a healthy, adult population and are not applicable to special populations like young children and the elderly. In reviewing existing data on current DF intakes of a population, the methods used for dietary assessment and chemical analysis of the DF content of a food are determined since they both influence the estimated intake level. Finally, recommendations are for DF in foods and not supplements. The use of DF supplements may affect the balance of nutrients in an otherwise healthy diet. Limited data exist on the effects of isolated DF which may differ from the DF naturally present in a food (30).
Worldwide Dietary Fiber Intake Recommendations |
Recommendations for DF intake by the World Health Organization (WHO) are t?
16-24 g/d of NSP or 27-40 g/d of TDF (Table 2). The Food and Agriculture |
Organization (FAO) of the United Nations (1995) recommends that individuals ^
should eat a variety of foods in order to obtain all the necessary nutrients for proper health (Table 3). Carbohydrates was one of seven food groups mentioned, with cereals listed as a choice. In contrast, the WHO Study group (33) advocated that complex carbohydrates should be a major portion of the diet at 50-70% of the total energy consumed. Suggested sources of NSP included fruits and vegetables (no less than 400 g/d) and pulses, nuts, and seeds (no less than 30 g/d but
Dietary Fiber Intake
Table 2 Dietary Fiber Daily Intake Recommendations
Source of recommendation
Central America 18-24 g
Italy Japan Mexico Netherlands
25 g/2000 kcal 30-40 g
NSP Report: Diet, nutrition and the pre-TDF vention of chronic diseases DF Australian Government Department of Community Services and Health
DF National Council for Nutrition (unofficial)
DF Expert Panel in 1985 (unofficial) DF Institute of Nutrition of Central
America and Panama (INCAP) NSP Health Ministry (1992) TDF National Food Agency/Nutrition Council
DF National Food Agency/Nutrition Council
DF French gastroenterologist-
unpublished DF German Society of Nutrition DF Indian Council of Medical Research, National Institute of Nutrition
DF The Food Advisory Committee of the Department of Health (1987) TDF National Nutrition Institute TDF Ministry of Health and Welfare DF National Nutrition Institute DF Dutch Nutritional Values 1989: Nutritional Council DF National Food Agency/Nutrition Council
DF Food and Drug Administration (FDA)
TDF Heart Foundation, Cancer Association, Association of Dietetics, Department of Health (unofficial)
TDF General literature references, no official figures DF National Food Agency/Nutrition Council
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Table 2 Continued
Source of recommendation
United Kingdom 18 g
United States United States
United States Venezuela
25 g/2000 kcal (adult) DF
"Age + 5'' to "Age + 10'' g (3-20 years of age) 0.5 g/kg BW up to 25 g/day (adolescents) 8-10 g/1000 kcal
NSP Department of Health Committee on Aspects of Food Policy, Department of Health Dietary Reference Values Report Food and Drug Administration (FDA)
American Health Foundation
DF American Academy of Pediatrics DF National Nutrition Institute (1993)
part of the 400 g recommendation for fruit and vegetables). The WHO further specified that free sugars should be no more than 10% of energy (33).
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