Dietary D. A.

fiber:

T Southgate,2

analysis

The

components

discussed

measurement species seems

in foods

would essential

in a range

of

in

relation

and

the

dietary to

diet

be a time-consuming to an understanding

of foodstuffs

of total

sources

dietary

is presented, fiber

Journal

of Clinical

Nutrition

fiber

their

sources1

Downloaded from https://academic.oup.com/ajcn/article-abstract/31/10/S107/4656072 by Queen Mary University of London user on 25 March 2018

reviewed

and

the

Complete

relative Am.

and

physiological

exercise; nevertheless of any physiological

is outlined.

31: OCTOBER

are

possible

as a whole.

The total intake of dietary fiber3 is derived from two sources: the structural materials of the plant cell walls present in the foods making up the diet; and nonstructural polysaccharides that occur naturally in foods (e.g., mucilages and gums) or are used as food additives (e.g., gums, algal polysaccharides, and modified celluloses) (2). Dietary fiber is a mixture of components, the composition of the mixture depending on the types of foods in the diet. Furthermore, the composition of the cell wall in many plants is dependent on the stage of maturity of the plant and on the cultural conditions under which the plants were grown. The major components of dietary fiber are listed in Table 1. The components themselves contain a range of types of chemical structures (Table 2); the complexity of this mixture making up dietary fiber is therefore very great if these variations are included. Any analytical procedure for the measurement of total dietary fiber must represent the compromise between a complete fractionation and measurement of all the various species present and a simplified system involving grouping of the different components in some arbitrary and often empirical way (3). Since the various approaches to the analysis of dietary fiber have been discussed in earlier papers and at length in recent reviews, they will not be repeated here. There are, however, some important points to be made about the analysis of dietary fiber. The original dietary fiber hypothesis relating diverticular disease to low fiber intakes (4) has been enlarged to include a wide range

The American

food

Ph.D.

ABSTRACT

intake

and

fractionation

chemistry

Nutr.

of all

of the 31: 5107-S

of

and

some characterization role. The composition

contributions

J. Clin.

the

properties

major

the

their

the

various analytical

polysacchanide

of dietary of the dietary food

groups

fiber fiber to the

1 10, 1978.

of other diseases in Western civilization (5). This expansion is related to several different types of physiological effects. It is unreasonable to expect all these effects to be caused by all the components of dietary fiber; indeed it is already apparent that the capacity of fiber to increase fecal bulk and reduce transit time is unrelated to any effect on serum cholesterol concentrations (6). Analogously, polysaccharides that can be shown to reduce serum cholesterol concentrations do not necessarily affect fecal bulk (7). It therefore seems essential to use methods that characterize the various components making up the total. If it can be shown that individual components are associated with specific physiological effects, it is probable that our aim should be the measurement of specific classes of polysaccharides and not the combined mixture. This would have the advantage of avoiding the confusion associated with the use of the term fiber for nonfibrous polysaccharides (8). It is vital, however, to avoid linking the definition of dietary fiber with any one empirical procedure in the way that crude fiber is linked. At the present time, and probably in the future, there is no one procedure that

‘From the Dunn Nutritional Laboratory, Medical Research Council and University of Cambridge, Milton Road, Cambridge CB4 IXJ, England. 2 Member of Scientific Staff, Medical Research Council. ‘In this context, dietary fiber is defined as the sum of the polysaccharides and lignin that are not digested by the endogenous secretions of the human digestive tract (1).

1978,

pp. S 107-S

110.

Printed

in U.S.A.

S107

SOUTHGATE

S 108

is appropriate for all types of foodstuffs or diets. Ultimately the method chosen will not be the one that is the simplest, nor the most rapid, nor the one that is most repeatable by analysts with a range of skills and experience, but the method that enables the measurement and characterization of dietary fiber in such a way that will predict and explain the physiological effects of the consumption of the mixture in question. Food

Characteristics foods

sources

Quantitatively the major part of dietary fiber is derived from cell wall materials in most diets although few detailed analyses have been made. The major food sources are therefore cereals, vegetables, fruits, and nuts. Calculations based on crude fiber data (9), TABLE Components Structural of the

1 of dietary

Other

fiber Noncellulosic polysaccharides Cellulose Lignin Gums and mucilages Algal polysacchanides Modified celluloses Protein, lipids, waxes, cutin, etc.

components plant cell wall

Nonstructural charides

polysac-

substances

TABLE Structural of dietary

features fiber

of the

fiber

in different

Cereals The dietary fiber content of cereals depends greatly on the degree to which the cereal has been refined. Wheat flour at the extraction rate used in bread making contains about 3 to 4% as measured by the method of Southgate (11, 12). As the extraction rate is increased, the total dietary fiber increases to the levels found in whole grain of between 11 and 14%. Other cereals are not usually consumed at a range of extraction rates, and some typical values are shown in Table 3. Table 3 also shows the composition of the total in terms of noncellulosic pohysaccharides, cellulose, and lignin. The composition of the noncelluhosic fraction varies according to the extraction rate and among the various

components

Noncellulosic

groupings

.

pohysaccharides

Pectin Gums,

mucihages

Algal

polysacchanides

Modified

Principal structural types

Galactunonans Arabinoand ronoxylans

glucu-

Glucoand gahactomannans Anabino galactans $-D-glucan Aromatic polymer

Cellulose Lignins Nonstructunal

of dietary

2

Major

Structural

which may be misleading, suggest that cereals provide about one-third to one-half the total fiber in the United Kingdom. The remainder is provided mainly by vegetables with minor contribution from fruits and nuts. Crude fiber values underestimate the contribution of dietary fiber from all foods but especially from refined cereals (10). We must await further calculations to assess the dietary fiber sources more appropriately.

celluloses

Downloaded from https://academic.oup.com/ajcn/article-abstract/31/10/S107/4656072 by Queen Mary University of London user on 25 March 2018

Galacturonans Great variety including arabino-xylans and glucoand galactomannans Sulphated galactans and gulurono-mannuronans Esters, ethers

Main

.

variations

Methoxy groups; side chains Branched and linear xylan chain; number and distribution of side chains Number and distribution of side chains Branching and side chains Degree of polymerization Type of polymer; functional groups Methoxy group; side chains Branching; side chains

Variations in the composition the back-bone chain Cross-linking

of

DIETARY

cereals. High-extraction rich in the polysaccharides nose and xylose.

FIBER:

wheat and containing

ANALYSIS

AND

rye are arabi-

Vegetables are eaten at high water contents, which effectively dilutes the dietary fiber so that with the exception of seed legumes the values for total dietary fiber in fresh vegetables are often less than 5% (10). All the vegetables we have examined contamed minor amounts of lignin; this is consistent with histological examination of these foods as consumed in the United Kingdom. 3 fiber

in some

SOURCES

Fruits The total appreciably

dietary lower

Total

dietary fibe

Noncellulosic poly. saccharides

of the fiber

Cellulose

Composition n oncellulosic

Lignin

g/10t7g

(72%) (90-95%) flour (100%)

TABLE Dietary

matter 4 fiber

5) is basis.

of fraction

Hexoses

Penioses

Uronic . acids

80 44 38 32 19 62 82 46

11 45 49 57 69 26 9 45

9 11 13 11 12 12 9 9

c

3.45 8.70 13.51

Bran, sieved Bran, coarse Oatmeal, for porridge Rice, long grain Rye, whohemeal product “Dry

fiber in fruits (Table on a fresh weight

cereals C omposition dietary

Wheat products White flour Brown flour Wholemeal

S109

In leafy vegetables collenchyma with nonlignified walls are a major element in maintaining the erect plant in contrast to the monocotyledonous grasses where lignified scherenchyma are important structural elements. Table 4 shows sOme typical values. In leafy vegetables the noncellulosic polysaccharides contain similar proportions of pentoses and uronic acids. Root vegetables on the other hand contain more uronic acids.

Vegetables

TABLE Dietary

FOOD

80 72 74 75 74 82 78 71

30.6 48.0 7.66 2.74 12.7

19 18 20 16 18 12 22 14

1 10 6 9 7 6 Tn 15

basis.

in some

raw

vegetables .

Total

dietary

Fresh weight

Composition . dietary

fiber

Dry . weight

Noncellulosic

.

.

Composition noncellulosic polysacchandes

of the fiber

Cellulose

Lignin

g/JOOg

Leafy vegetables Brocolli tops Brussels sprouts Cabbage, winter Cabbage, white Onions

.

Hexose

Pentose

of the .

Uronic acid

%

3.60 4.22 3.44 2.66 1.30

32.7 35.5 29.4 27.4 18.1

76 72 62 66 74

23 25 25 23 26

1 3 13 11 Tn

15 17 9 7 29

42 48 47 42 26

44 35 43 50 45

7.75 6.28 2.90

37.1 34.1 26.4

69 61 52

27 39 42

2 Tn 7

48 23 20

22 30 42

30 47 39

2.90 2.40 3.41

28.4 22.1 14.1

60 67 71

40 33 29

Tn Tn 1

20 17 80

35 28 ND.

45 55 20

Legumes Peas,

frozen

Peas, canned Runner beans Root vegetables Carrots Swedes

Potato

Downloaded from https://academic.oup.com/ajcn/article-abstract/31/10/S107/4656072 by Queen Mary University of London user on 25 March 2018

SOUTHGATE

SIlO TABLE Dietary

5 fiber

in some

fruits

(edible

Tota

matter

1 dietary

Fresh weight

only) Composition dietary

fiber

Dry weight

Composition noncellulosic polysaccharides

of the fiber

Noncellulosic

Cellulose

66 64 74 78 71 64 54 65 46 47

33 21 20 9 14 9 28 15 16 32

Lignin

of the

Hexose

Peniose

Uronic acid

20 54 25 17 19 21 20 28 22 14

35 19 35 43 37 38 46 46 33 42

44 27 39

s//flog Apple, flesh Banana Cherry” Grapefruit, canned Orange Peaches” Pears Plums” Strawberries Tomato, fresh” “Skin

included

1.42 1.75 1.24 0.44 1.90 2.28 2.44 1.52 2.12 1.40 in edible

9.16 5.97 6.70 2.42 13.7 16.5 14.7 9.56 19.1 21.9

Barbara Bailey and Mrs. the values reported in this

with

physiology 2.

Calculations made from average food intakes and the application of the same methods to mixed diets show that, with the usual diet eaten in the United Kingdom and the United States, the average individual intake is about 20 g/day. Diets rich in whohewheat cereals may contain up to 35 g/day, but these are relatively low levels compared with, for example, the plantain banana diet typical of Uganda where preliminary calculations suggest over 100 g/day. In the diets we have examined, hignin vatues were very low, even with diets that had been cooked and may, therefore, have included hignin artifacts. Few studies have been reported where it is possible to identify the effects of specific polysaccharides, but studies with bran show that fecal excretion of pentose containing noncelluhosic polysaccharides may increase by a factor of3 to 4 (13). Uronic acid concentrations in feces are usually very how, which may explain why pectin does not have any effect on fecal bulk. The understanding of more specific relationships will depend on metabolic studies with defmed dietary fiber sources that may have been carefully characterized.

a

The

author

acknowledges

the

parts

played

by

Mrs.

Downloaded from https://academic.oup.com/ajcn/article-abstract/31/10/S107/4656072 by Queen Mary University of London user on 25 March 2018

Edna paper.

Collinson

in

obtaining

References 1. TROWELL, EVER, A.

of fiber

40 43 41 35 25 45 44

portion.

Lignin values are low except when lignified seeds are eaten or when skins are consumed because cutin has been analyzed with the hignin. Correlation

1 15 6 13 15 27 19 19 38 21

3.

4.

5.

6. 7. 8.

9. 10.

1 1.

12.

13.

H.,

M. S. W0LD. A. JENKIN5. Dietary fibre redefined. Lancet I: 967, 1976. SOUTHGATE, D. A. T. The chemistry ofdietary fiber. In: Fiber in Human Nutrition, Edited by G. A. Spiller and R. J. Amen. New York: Plenum Press, 1976, pp. 3 1-72. SOUTUGATE, D. A. T. The analysis of dietary fiber. In: Fiber in Human Nutrition, edited by G. A. Spiller and R. J. Amen. New York: Plenum Press, 1976, pp. 73-107. PAINTER, N. S., AND D. P. BURKITr. Diverticuhar disease of the colon. A deficiency disease of Western civihisation. Brit. Med. J. 2: 450, 1971. BURKITF, D. P., AND H. C. TROWELL. Refined Carbohydrate Foods and Disease. New York: Academic Press, 1975. TRUSWELL, A. S., AND R. M. KAY. Absence of effect of bran on blood lipids. Lancet I: 922, 1975. TRUSWELL, A. S. Food fibre and blood lipids. Naringsforskning (Suppl. 1420): 5 1, 1976. SPILLER, 0. A., AND R. J. AMEN. Plant fibers in nutrition. Need for better nomenclature. Am. J. Chin. Nutr. 28: 675, 1975. ROBERTSON, J. Changes in fibre content of the British diet. Nature 238: 290, 1972. SOUTHGATE, D. A. T., B. BAILEY, E. C0LLIN50N AND A. F. WALKER. A guide to calculating intakes of dietary fibre. J. Human Nutr. 30: 303, 1976. SOUTHGATE, D. A. T. The determination of carbohydrates in food. II. Unavailable carbohydrates. J. Sci. Food Agric. 20: 331, 1969. SOUTHGATE, D. A. T. Determination of Food Carbohydrates. London: Applied Science Publishers, 1976. SOUTHGATE, D. A. T., W. J. BRANCH, M. J. HILL, B. S. DRASER, R. L. WALTERS, P. 5. DAVIES AND I. R.

D. A. T. SOUTHGATE, M. A. GASSUL

LEEDS,

MCLEAN

BAIRD.

plements

of bran.

Metabolic

Metabolism

responses

T.

AND

to dietary

10: 1129,

1976.

sup-

Dietary fiber: analysis and food sources.

Dietary D. A. fiber: T Southgate,2 analysis The components discussed measurement species seems in foods would essential in a range of in...
453KB Sizes 0 Downloads 0 Views