Adequate Intake of Fiber

1. Adequate Intake of Fiber By Anna Bondy

2. Sources of Fiber • Any food that comes from a plant source has fiber • This includes fruits, vegetables and whole grains • In order to maximize fiber from these sources, it is suggested that they are eaten in their least processed form • Whole fruit instead of fruit juice • Whole grains flours instead of processed flours • Uncooked vegetables

3. Types of Fiber • The latest report from the Food and Nutrition Board uses the terms Dietary Fiber & Functional Fiber • Nutrition labels use soluble and insolublefiber

4. Functional Fiber • The USDA is in the process of identifying functional fibers – fibers with certain physiological benefits including: • Laxation • Normalization of blood lipid concentrations • Attenuation of blood glucose responses Bananas are a source of resistant starch, a functional fiber

5. Potential Functional Fibers

7. Functions of Fiber • Viscous fibers, such as gums and pectins, delay gastric emptying and prolong absorption in the small intestine, causing a longer feeling of fullness and decreased energy absorption • Nonviscous fibers include cellulose and lignin Beans are high in pectin, a viscous fiber

8. Functions of Fiber • Fermentable fibers, such as pectins, β-glucans, inulin and oligofructose, provide energy for microflora in the colon in the form of butyrate, which may be related to increased colon health and decreased risk of colon cancer • Nonfermentable fibers include cellulose Steel-cut Oats

9. Symptoms of Deficiency • Technically, there are no biochemical or clinical symptoms of fiber deficiency • Constipation, weight gain, blood sugar fluctuations, diet-related nausea • Can result in “inadequate fecal bulk and may detract from optimal health” (24) • Sufficient fiber intake is more important for quality of life later in life in the elderly

10. Symptoms of Toxicity • No UL established for fiber but still has adverse effects in large quantities (57) • Phytate in fiber rich foods can decrease the bioavailability of iron, calcium, zinc, and other trace metals (53-54) • Intakes far above the AI for fiber resulted in increased flatulence and excessive abdominal fullness (56-57)

11. Biochemical Basis of Symptoms • Inadequate fiber consumption may result in constipation because fiber is responsible for: • Softening stool • Adding bulk to stool • Speeding up the passage of stool through the colon

12. Biochemical Basis of Symptoms – Glycemic Control • When large bursts of glucose enter the blood, beta cells in the pancreas respond by secreting more insulin • Constant elevations in blood glucose is thought to increase the risk for Diabetes Mellitus • Meals high in fiber lower insulin levels over time because they promote smaller, sustained releases of blood glucose

13. Biochemical Basis of Symptoms – Coronary Heart Disease • Recent studies have shown that increased consumption of dietary fiber may decrease the amount C-reactive protein circulating in the blood. C-reactive protein is a biomarker for inflammation that is strongly associated with the risk of myocardial infarction and stroke. Molecular Model of C-reactive protein

14. Biochemical Basis of Symptoms – Decreased Lipid Levels • Interferes with reabsorption of bile acids and cholesterol and recirculation through the liver. • 15 g pectin increased net cholesterol excretion by 14 percent

15. Research Study Objective • The Alpha-Tocopherol, Beta Carotene Cancer Prevention (ATBC) Study was a collaborated effort • Pietinen used this cohort of Finnish men as a source of data to compare fiber intake and risk of cardiac events.

16. Characteristics of subjects or populations • The subjects in this study were all Finnish men, ranging in age from 50 to 69 at the beginning of the study in 1985. All of the participants were smokers. • The Finnish population was chosen specifically by Pietinen due to the frequent consumption of rye bread and other high-fiber foods.

17. Design of Study • Randomized, double-blind, placebo-controlled primary prevention study • Subjects provided personal health histories, filled out a food frequency questionnaire and gave feedback on exercise frequency, educational background and cigarettes smoked per day. • Pietenen chose subjects that had completed food frequency questionnaires and divided the sample into quintiles based on their dietary fiber intake

18. Chemical and Biological Assays • No biological or chemical assays can directly measure fiber status because fiber is not absorbed • Instead they measured: • Blood pressure • Serum total cholesterol • HDL cholesterol

19. Table 1. Relation of Energy-Adjusted Dietary Fiber Intake to Selected Coronary Heart Disease Risk Factors and Intake of Nutrients and Foods at Baseline*

21. *Adjusted for age (5-y categories); treatment group; smoking; body mass index; blood pressure; intakes of energy, alcohol, and saturated fatty acids (quintiles); education (<7, 7 to 11, and >11 y); and physical activity (<1, 1 to 2, and >2 times per week).

24. AI for Fiber • It is possible to set a recommended intake level for fiber because of the prospective studies done by Pietinen (1996), Rimm (1996) and Wolk (1999). All of these studies divided subjects into quintiles of fiber intake and provided data on energy intake, so that a recommendation could be made based on grams of fiber per 1000 kilocalories per day.

25. In Pietenen’s study of 21,930 Finnish men, the group with the highest dietary fiber intake consumed 34.8 g/d. These men have a median energy intake of 2,705 kilocalories per day. Therefore they consumed 12.9 g of Dietary Fiber per 1,000 kilocalories. (Pietinen et al., 1996). Looking at all three studies collectively, data suggests that 14 g of Dietary Fiber/1,000 kilocalories, particularly from cereals, is optimal to promote heart health. • Intervention trials and epidemiological studies have come to similar conclusions. • An EAR cannot be set because dietary fiber has an impact on CHD rates across a range of intakes.

26. Based on the data for average dietary fiber intake and its effect on CHD, as well as the beneficial effects of functional fibers, an AI for total fiber can be set for age and gender groups. • This is done by multiplying 14 g/1000 kcal by median energy intake (kcal/1,000 kcal/day). To set the AI for those between the ages of 19 to 50 years and 50 years and older, the highest median intake level for each group was used. There is no research that indicates that the relationship between fiber and energy intake change during the life cycle.

27. Questions?

28. Bibliography • Fiber: Start Roughing it. (2010). Harvard School of Public Health. http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/fiber-full-story/index.html • Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients) (2005). National Academy of Sciences. Institute of Medicine. Food and Nutrition Board. Retrieved from http://www.nal.usda.gov/fnic/DRI//DRI_Energy/339-421.pdf • Higdon, J. Fiber. (2010) Linus Pauling Institute at Oregon State University. Retrieved from http://lpi.oregonstate.edu/infocenter/phytochemicals/fiber/ • Kovacs, B. (2007). Fiber facts, types, function, benefits, dietary requirements. MedicineNet. http://www.medicinenet.com/fiber/page2.htm • Fries, W.C. (2010). 4 Warning Signs that your diet may lack fiber. WebMD. Retrieved 6 Nov 2010 from http://www.webmd.com/food-recipes/features/4-warning-signs-your-diet-may-lack-fiber • Pietinen, P., Rimm, E.B.,  Korhonen, P., Hartman, A.M., Willett, W.C. Albanes, D., Virtamo, J. (1996). Intake of Dietary Fiber and Risk of Coronary Heart Disease in a Cohort of Finnish Men: The Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study. Circulation. 94:2720-2727. Retrieved from http://circ.ahajournals.org/cgi/content/full/circulationaha;94/11/2720