Content and composition of dietary fiber in 117 frequently consumed foods

Twenty-three fruits, 33 vegetables, 41 grain products, 7 legumes, 4 nuts, and 9 miscellaneous foods were analyzed by an accurate chemical method to determine their dietary fiber content and composition. The mean (+/- standard deviation) dietary fiber content of fruits was 1.4 +/- 0.7 g/100 g (fresh weight); of vegetables, 2.0 +/- 0.8 g; of 32 refined grains (less than 5% fiber), 2.3 +/- 1.0 g; of legumes, 4.0 +/- 0.7 g; and of nuts, 6.4 +/- 2.1 g; the dietary fiber content of nine higher-fiber grains (greater than 5%) was variable. The soluble fiber fraction averaged 23% of the total fiber in refined grains, 3% in nuts, and 13% to 20% in the other food groups. Dietary fiber composition of every food group was heterogenous. Pectin, which was negligible in grains, constituted approximately 15% to 30% of the fiber in fruits, vegetables, legumes, and nuts. Hemicelluloses composed about half of the total fiber in grains, and approximately 25% to 35% of total fiber in other foods. Cellulose was one third or less of the total fiber in most foods, except for legumes, in which it was about one half. Values for total dietary fiber content generally agree with those reported previously. The soluble fiber fraction was lower than what has been reported because the distribution of total fiber between the soluble and insoluble fractions is determined by the method of analysis. The analyses used in this study demonstrated that the concentration of dietary fiber in many frequently consumed foods is 1% to 3%. The generally similar fiber concentrations of food within a group--fruits, vegetables, refined grains, and legumes--suggest that an average value for the fiber concentration in that group can be used to rank food intakes and histories into low, medium, or high dietary fiber contents.