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Page 1

MEDICAL ASPECTS
OF DIETARY FIBER

Page 2

TOPICS IN GASTROENTEROLOGY

Series Editor: Howard M. Spiro, M.D.
Yale University School of Medicine

PANCREATITIS
Peter A. Banks, M.D.

MEDICAL ASPECTS OF DIETARY FIBER
Edited by Gene A. Spiller, Ph.D., and Ruth McPherson Kay, Ph.D.

NUTRITION AND DIET THERAPY
IN GASTROINTESTINAL DISEASE
Martin H. Floch, M.S., M.D., F.A.C.P.

A Continuation Order Plan is available for this series. A continuation order will bring
delivery of each new volume immediately upon publication. Volumes are billed only upon
actual shipment. For further information please contact the publisher.

Page 155

140 ION A. STORY

adsorption is real and is independent of the water-holding capacity of dietary
fiber. Gross binding is, however, definitely influenced by the amount of solute
held by absorbed solvent.

Adsorption of bile salts from micellar suspensions was first attempted by
Balmer and Zilversmit.22 They observed that a stock diet and several dietary-
fiber-containing components of a stock diet (alfalfa meal, ground wheat, corn,
etc.) bound significant quantities of both cholesterol and taurocholate from
micelles.

Eastwood and Mowbray23 subsequently examined adsorption of micellar
components from micelles typical of those found in various parts of the small
intestine. They found that adsorption is minimal in the jejunum where micelles
are rich in the products of triglyceride digestion. In the ileum, adsorption is
more likely to affect bile-salt absorption. In the large intestine, the amount of
adsorption is dependent on the relative amounts of primary and secondary bile
acids which, in turn, are partly determined by the microflora activity of the
cecum and large intestine. This activity is also affected by the source and
amount of dietary fiber present.

Recently, Vahouny et al. 24 have also examined the binding of bile salts
and cholesterol by several sources of dietary fiber in micellar solutions. Alfalfa
meal bound 10% of micellar cholesterol and displayed a preference for uncon-
jugated bile acids. Cellulose and bran did not bind bile salts, but bran did bind
a significant portion of micellar cholesterol present (38%). These results indi-
cate an in vitro interaction of alfalfa and bran with micellar lipids. The exact
role this effect might play in lipid absorption is not clear, since previous studies
with alfalfa and bran showed only alfalfa to be hypocholesteremic.

Since the adsorption phenomenon appears to be real and not just an arti-
fact of water absorption, an examination of the effects of particle size on
adsorption should be revealing. Burczak and Kellogg25 have recently examined
the role of the particle size of oats and wood particles and their bile-acid-
adsorption properties. Wood-shaving particle size was very closely related to
the amount of bile acid (cholate, deoxycholate, and chenodeoxycholate)
adsorbed, with adsorption increasing as particle size decreased. They did not
observe the same relationship with oats, in spite of a higher level of adsorption.
Deoxycholate adsorption seemed to be related to particle size, but cholate and
chenodeoxycholate adsorption were not. Use of the Eastwood et al.2l washing
method might have indicated a difference in the real adsorption of all mate-
rials. If we are to ascribe adsorption of bile acids by dietary fiber to any of the
classical adsorption mechanisms, surface area should definitely alter the
amount of adsorption. Particle size is a simplistic method of altering surface
area. A more thorough examination of this relationship should help shed light
on the nature of the adsorption mechanism. Until then, measurement and con-
trol of particle size are steps toward avoiding confusion and misinterpretation
of results.

Page 156

DIETARY FIBER AND LIPID METABOLISM 141

A question of the importance of saponins in the adsorption process has
been raised by Oakenfull and Fenwick.26 Their data indicated that only mate-
rials containing saponin adsorbed bile acids in the system used. Additionally,
extraction of saponins with 80% ethanol resulted in a loss of adsorption by these
materials. Several points of disagreement between the data presented and those
presented previouslyI7·18 need to be clarified. The pH of bile-acid solutions used,
much lower than those used by others, has been shown to decrease adsorption. 17

Lignin, isolated by several methods, has been shown by other workers to adsorb
bile acids. I7,20,27 This lack of adsorption of lignin26 cannot be easily explained.
These data emphasize the importance of control of methodology and attention
to detail in organization of investigations.

Currently, we have examined the bile-acid adsorption of alfalfa and bran
using a modification of the Eastwood et al.method.21 Using two extraction
schemes, we have sequentially removed various fractions of the plant material
and measured the adsorption of the remaining fraction (Table 2). Adsorption
was enhanced by the removal of saponins, possibly as a result of concentrated
adsorbing components. No appreciable reduction in adsorption was seen until
delignification, regardless of the extraction scheme used. These findings agree
with earlier experiments conducted by Eastwood and Hamilton l7 and seem to
be in direct conflict with the work reported previously by Oakenfull and
Fenwick.26

Adsorption of bile acids by dietary fiber appears to be a key characteristic
in its effects on lipid metabolism. However, we still face many problems in
understanding the exact nature and mechanisms of adsorption. Careful control
of conditions and materials used in adsorption will help solve these problems.

Table 2. Adsorption of Deoxycholic Acid by Various Fractions of Alfalfa and Bran'

Alfalfa Bran

Fraction 2.5mM 5.0mM 2.5mM 5.0mM

Scheme 1
Whole plant material 1.00 (38.3)' 1.00 (38.4)' 1.00 (38,2)' 1.00(32.0)'
Less fat solubles 0.91 0,97 0.97 1.09
Less saponins 1.09 1.13 1.25 1.52
Less pectins 0,98 1.01 1.04 1.20
Less lignin 0.32 0,34 0,36 0.36

Scheme 2
Whole plant material 1.00 (38,2)' 1.00 (35.9)' ND ND
Less saponins 1.09 1.20
Less pectins 1.00 1.12
Less lignin 0,34 0.25

'3 ml ['H]deoxycholate (2.5 or 5.0 mM) in phosphate buffer (pH 8.0) incubated with 100 mg adsorbing
material.

'Whole plant material taken as 1.00. Actual percentage adsorption given in parentheses.

Page 309

298

Hemicelluloses, 5, 9, 15,17-19,84,101,105,
108, 123, 130, 143, 156, 254, 264

Hepatic (entero-, ileo-, ceco-) circulation, 2-
3, 12-13,31,161

Hormones, 28, 37-38,72-73,163,185,210-
213

gastric inhibitory peptide (GIP), 37, 180,
211,231

Hydrazines, 87-88, 92-93, 99-100,104-105,
107, 110

Hydrogen (breath), 17-19,30-31
Hyoscyamine, 57, 59
Hyperglycemia, 194
Hyperinsulinemia, 230-231
Hypertriglyceridemia, 203-206, 208, 213-

214,216-217
Hypoglycemia, 189,196,213-215,231

Ileum, 2, 30, 55, 69-70, 88, 90,140,246-247
Insulin, 176-180, 185, 188- I 90, 195- I 96,

199,201,205-208,211-214,217,
230-232, 236

insulinogenesis, 230-232, 236
Intestine, small, 28-30, 33-34, 67-73, 78,

88-90,94,103,106,109,140,210,
213,231,233,240,247,262-263

Ions, 14, 16-17,39,243,252
anions, 10
cations,S, II, 39, 51, 242-246

Iron, 11, 209, 239, 242-243, 252, 254-256

Jejunum, 3, 12, 67, 70-71, 88, 140, 246

Lactulose, 18, 30-31, 160, 178-179, 182-183
Laxatives, 55, 57, 109, 126
Lignin, 9, 16, 18,84-85, 101, lOS, 108-109,

Ill, 123, 130, 141-142, 156, 160,
240, 264, 266-267

Lipids, 109, 137, 140, 142, 146, 148, 154,
159, 162-163,213

biliary, 153, 160, 165
metabolism of, 137-138, 142-143, 145,

148, 153-154, 159, 166,201,209-
210,212

plasma, 153, 155-159, 162, 164-166,201
serum, 142, 154-155, 157,201,217

Lipoproteins, 146,148,153,163,213
high-density (HDL), 146, 158, 163,202-

203,208,212
low-density (LDL), 146, 153, 158-159,

163,202-203, 208, 212-213
plasma, 6-7,153,161,167

INDEX

Liver, 2,31,87,98-99,138, 144-145, 161,
213, 230, 250

Lumen, 2, 4, 18,39,51,53,69, 88, 98,
109

Metabolism, see specific substance
Methane (breath), 17-19,30
Methylcellulose, 31,58,157,177,179,183
Microflora, see Microorganisms
Microorganisms, 2-7, 9,11,13-14,16,30,

38,50,69-73,78,88,110,123-124
effect of fiber on, 3, 14,50-51,110, 129
metabolism by, 14-15, 18, 72, 108, 210,

248
Minerals (see also Calcium, Iron, Zinc), 4,

11,51,69,209,214,239-256
fecal output of, 2, 51, 39, 247
malabsorption of, 208-209, 214, 240, 247

Mucosa, 2,14,18,39,49,52,67,69,72-73,
78, 85-86, 88, 90, 93-94, 98, 100,
103, 107-109,212,247-248,254

Mucus (mucins), 93-94,97-99, 102-103

Neoplasia, 86, 88, 91-95, 98-99,101-108,
110,119-120

Oatmeal (oats), 140, 146, 159, 166,202,239,
242

Obesity, 60,154-155,162,223-225,230,
233-236,261

Pectin, 5-6, 13, IS, 18, 22, 31, 33, 69-72, 84,
105, 109, 123, 130, 141, 143-144,
146,156-157,160,163-166,177-
180,182-184,189,202,231-233,
239, 244, 247, 254-255

Peristalsis, 18, 28
Phytate, 239-255
Plantix, 84, 130
Polyps, 76-77, 94-95, 98-99, 103
Polysaccharides, 10, 15-16,22,31,72,84,

143, 239, 242, 262-264, 268, 273-
274

Protein, 38, 68, 77, 79, 101, 123, 147, 154,
159, 162, 167,246,254

Rectum (anus, anal), 1-2,7,27,31,37-38,
50,55,77,87,98, 102

Saponins, 12, 141, 147, 159
Starch, 15,80,230-232,236,262-264
Sterculia, 54, 58-59

Page 310

INDEX

Steroid,38, 143, 145, 161
fecal (excretion), 6-7, 138, 143-146, 161,

164-166
Sterols, 12-13, 109, 159, 161, 163-164
Stomach, 27-29,75,88, 184, 188,215,227
Stool, see Feces
Sugars, 15-16,77,123,127,144, 146, 159,

182,186,210,225-226,228-229,
231,233-236,270

Surgery, 1,30,52,57-58,69,184

Tragacanth, gum, 31, 177, 179-180, 182-183
Transit, 4, 27, 36-39, 47, 52, 58-59,182,

184-185
colonic, 28, 34, 37
influence of fiber on, 6-7,13,29-30,32-

34,36-37,40,59,109,129,145
measuring, 29-36, 39-40
mouth-to-cecum, 30-31, 182
small-intestinal, 37,232
total (transintestinal), 27,31-32,38,50,

188,210
Triglyceride, 140, 142, 155, 157, 162-163,

193,203-204,206-208,210,213,
216-217,233

299

Urine, 38, 180-182, 186, 190, 195, 199-201,
205

Vegetables (and specific vegetables), 5-11,
13-14,17,22,32-33,46,48,77,79,
125, 127-128, 131, 139, 159, 16~
176,198,215-216,224,227,230-
232,244,264-279,281-282

Vegetarians (vegetarian diet), 47-48, 68, 79,
120, 131, 154,265,274-275,279

Villi, 67-70, 72, 94,100,103

Water, 2,4,9, 14, 16,22,50, 140,210,224,
246

White bread (flour), 29, 159,225-228,233,
241,243,251,255,265,267,269,
272

Whole-grain (brown) bread (flour), 29, 79,
158,198,216,225-228,231-232,
235,239-243,245,250-253,255,
265-266,273,275

Xylose, 178-182

Zinc, 11,239,243,245,247,252-254,256

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