Whole Grains and their Bioactives E-Book
167,99 €
Mehr erfahren.
- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
A review of various types of whole grains, the bioactives present within them, and their health-promoting effects
As rates of obesity and other chronic conditions continue to rise, so too does the need for clear and accurate information on the connections between diet and disease, particularly regarding the cereal grains that dominate the Western diet. In this volume, editors Jodee Johnson and Taylor Wallace assemble a panel of leading experts to address this issue. The result is a comprehensive examination of the cereal and pseudo-cereal grains and their most important bioactive compounds.
Not only does this volume offer summaries of existing research, it also places these findings within the larger context of health promotion and disease prevention. This includes frank discussions on the limitations of existing studies, as well as current gaps in research for those who want to offer evidence-based recommendations to their patients. Topics addressed include:
- Methodical analyses of domesticated grain species, their horticultural history, nutritional composition, and known effects on health
- Beneficial properties of certain bioactive compounds found in particular grain species
- How bioactive compounds work within an individual’s overall diet to increase health and prevent disease
Academic and industry researchers, as well as medical practitioners and public health professionals, will appreciate Whole Grains and their Bioactives, not only as an engaging overview of current research, but also as an illuminating contribution to the often-murky debate surrounding health and the human diet.
Sie lesen das E-Book in den Legimi-Apps auf:
Seitenzahl: 1078
Veröffentlichungsjahr: 2019
Ähnliche
Table of Contents
Cover
List of Contributors
Part I: Introduction
1 Introduction to Whole Grains and Human Health
1.1 History of Whole Grains
1.2 Who Consumes Whole Grains?
1.3 What are Whole Grains?
1.4 Components of Whole Grains
1.5 Whole Grain Bioactives
1.6 Health‐Promoting Effects of Whole Grains
1.7 Conclusion
References
Part II: Whole Grains,Whole Food Nutrition
2 Wheat
2.1 Introduction
2.2 History of the Grain
2.3 Types
2.4 Nutritional Composition
2.5 Health Effects on Chronic Diseases
2.6 Conclusion
References
3 Oats
3.1 Introduction
3.2 Nutritional Composition
3.3 Health Effects in Chronic Diseases
3.4 Conclusion
References
4 Rice
4.1 Introduction
4.2 History of Whole Grain Rice
4.3 Variety in Whole Grain Rice Quality and Preferences
4.4 Nutritional Composition and Bioactive Compounds in Whole Grain Rice
4.5 Whole Grain Rice Consumption and Prevention Against Chronic Disease
4.6 Whole Grain Rice Consumption and Protection Against Gut Pathogens
4.7 Conclusion
Acknowledgments
References
5 Corn
5.1 Introduction
5.2 Macro‐ and Micronutrients in Corn
5.3 Corn Phytochemicals
5.4 Health Benefits
5.5 Conclusion
References
6 Barley
6.1 Introduction
6.2 The Beginning
6.3 The Whole Grain Barley Kernel
6.4 Health Effects of Bioactive Compounds in Barley on Chronic Diseases
6.5 Conclusion
References
7 Rye
7.1 Introduction
7.2 Types
7.3 Consumption
7.4 Epidemiological Studies of Rye Intake
7.5 Rye Products
7.6 Nutritional Composition
7.7 Phytochemicals
7.8 Rye Fiber
7.9 Health Effects on Chronic Diseases
7.10 Gut Health
7.11 Cancer
7.12 Conclusion
References
Part III: Pseudo Cereal Grains, Whole Food Nutrition
8 Amaranth
8.1 Introduction
8.2 History of Amaranth
8.3 Amaranth Genetic Diversity
8.4 Amaranth Plant Physiology
8.5 Amaranth Seed Morphology
8.6 Amaranth Seed Chemical Composition and Nutritional Properties
8.7 Phytochemical Compounds in Amaranth Seeds
8.8 Amaranth Seed Storage Proteins
8.9 Health Effects of Amaranth Grain
8.10 Conclusion
References
9 Buckwheat
9.1 Introduction
9.2 History of the Grain
9.3 Nutritional Composition of Buckwheat
9.4 Metabolism and Bioavailability
9.5 Health Effects on Chronic Diseases
9.6 Conclusion
Acknowledgments
References
10 Quinoa
10.1 Introduction
10.2 History of the Quinoa Grain
10.3 Types of Quinoa
10.4 Nutritional Composition
10.5 Phytochemicals/Bioactives and Antinutritional Factors
10.6 Health Benefits
10.7 Food Applications
10.8 Future Prospects
10.9 Conclusion
References
Part IV: Health-Promoting Properties of Whole Grain Bioactive Compounds
11 Avenanthramides
11.1 Introduction
11.2 Presence in Whole Grains
11.3 Chemical Structure and Biosynthesis
11.4 Effects of Processing
11.5 Absorption, Distribution, Metabolism, and Excretion
11.6 Health Benefits
11.7 Conclusions and Future Research
References
12 β‐Glucans
12.1 Introduction
12.2 Presence and Distribution in Whole Grains
12.3 Chemistry
12.4 Mechanisms of Action
12.5 Effects of Processing
12.6 Conclusion
References
13 Phenolic Acids
13.1 Introduction
13.2 Presence of Phenolic Acids in Whole Grain
13.3 Factors Affecting Phenolic Acid Content in Grains
13.4 Bioaccessibility and Bioavailability of Grain Phenolic Acids
13.5 Health Benefits of Grain Phenolic Acids
13.6 Conclusion
References
14 Carotenoids
14.1 Introduction
14.2 Chemistry
14.3 Presence in Whole Grains
14.4 Dietary Databases
14.5 Bioavailability
14.6 Effect of Processing, Storage, and Environment
14.7 Conclusion
References
15 Alkylresorcinols
15.1 Introduction
15.2 Chemistry and Nomenclature
15.3 Presence of Alkylresorcinols in Cereals
15.4 Effect of Food Processing on Alkylresorcinols
15.5 Measuring Alkylresorcinols
15.6 Intake of Alkylresorcinols
15.7 Bioavailability and Pharmacokinetics of Alkylresorcinols
15.8 Biological Effects of Alkylresorcinols
15.9 Mechanisms of Action
15.10 Use of Alkylresorcinols and Their Metabolites as Biomarkers of Whole Grain Intake
15.11 Conclusion
References
16 Lignans
16.1 Introduction
16.2 Presence in Whole Grains
16.3 Chemistry
16.4 Metabolism of Lignans by Human Gut Microbiota and Bioavailability
16.5 Biological Activities
16.6 Impact of Agronomic Factors on Lignan Content in Foods
16.7 Effect of Processing
16.8 Safety
16.9 Conclusion
Acknowledgments
References
17 Phytosterols
17.1 Introduction
17.2 Chemistry
17.3 Presence in Whole Grains
17.4 Bioaccessibility and Bioavailability
17.5 Mechanisms of Action
17.6 Effect of Processing
17.7 Conclusion
References
18 Phytic Acid and Phytase Enzyme
18.1 Introduction
18.2 Food Sources of Phytic Acid
18.3 Phytase
18.4 Classification of Phytase
18.5 Factors Influencing Phytase Bioefficacy
18.6 Source of Phytase
18.7 Beneficial Health Effects of Phytate
18.8 Conclusion
References
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Examples of dietary bioactives found in whole grains and their postula...
Chapter 2
Table 2.1 US common wheat market classes, based on grain color (red or white), e...
Table 2.2 Nutritional composition (%) of different classes of wheats.
Table 2.3 Nutritional composition of different milling fractions of soft white w...
Table 2.4 Percent composition of lipids in wheat kernels and their fractions.
Table 2.5 Nutritional composition (%) of hulled wheats.
Table 2.6 Essential trace element composition and distribution within the bread ...
Table 2.7 Vitamin composition of wheat flour (μg/g dry matter).
Chapter 3
Table 3.1 Nutrient composition and energy content of coarse grains.
Table 3.2 The amino acids in oats and other main cereals.
Chapter 4
Table 4.1 Representative whole grain rice varieties and selected quality feature...
Table 4.2 Lipids identified in whole grain rice with selected spectra of bioacti...
Table 4.3 Amino acids identified in whole grain rice with selected spectra of bi...
Table 4.4 Vitamins/Cofactors and phytochemicals identified in whole grain rice w...
Table 4.5 Whole grain rice or components evaluated in human clinical trials for ...
Table 4.6 Whole grain rice consumption in human clinical trials involving cancer...
Chapter 5
Table 5.1 Nutrient profiles of corn and sweet corn (data reported on wet basis)
a
Table 5.2 Free, soluble, and bound forms of different phenolic acids in yellow d...
Table 5.3 Major phenolic acids content in yellow, Mexican blue, American blue, a...
Table 5.4 Carotenoid content of white, yellow, red, blue, and high‐carotenoid co...
Table 5.5 Vitamin E content in yellow corn [69].
Chapter 6
Table 6.1 Ranges of concentrations of phytochemical and dietary fiber components...
Table 6.2 Mean and range of total dietary fiber and β‐glucan content reported in...
Table 6.3 Total carotenoid, lutein, and zeaxanthin (mg/kg) content reported in d...
Table 6.4 Range of total, free, and bound phenolic content (μg/g) reported in ba...
Table 6.5 Range of total anthocyanin (μg/g) content reported in barley genotypes...
Table 6.6 Mean and range of total tocopherol (tocopherol + tocotrienol) and % to...
Chapter 8
Table 8.1 Proximate composition of amaranth species.
a
Table 8.2 Proximate composition of amaranth and different cereal seeds.
a
Table 8.3 Mineral and vitamin content in the seed of edible amaranth species.
Table 8.4 Crude fat and fatty acid content of amaranth seed oil.
a
Table 8.5 Amino acid profile from seeds of edible
Amaranthus
species.
a
Table 8.6 Protein quality of raw and processed amaranth.
Table 8.7 Predicted biological activity of amaranth seed proteins.a
Chapter 10
Table 10.1 Proximate composition of quinoa.
Table 10.2 Essential amino acid profile of quinoa (g/100 g protein).
Table 10.3 Fatty acid composition in quinoa (g/100 g, db).
Table 10.4 Bioactive compounds present in quinoa.
Table 10.5 Recent studies indicating the effect of quinoa supplementation on cho...
Table 10.6 Recent reports of various food products enriched with quinoa seed/flo...
Chapter 12
Table 12.1 Characteristics of cereal β‐glucans.
Table 12.2 Sources and conditions of use for oat and barley β‐glucan cholesterol...
Chapter 13
Table 13.1 Five hydroxycinnamic acid contents in 11 whole grains (µg/g dry weigh...
Table 13.2 Five hydroxybenzoic acid contents in 11 whole grains (µg/g dry weight...
Chapter 14
Table 14.1 Carotenoid content of whole grains (μg/100 g dry weight) [38].
Chapter 16
Table 16.1 Lignans (secoisolariciresinol, matairesinol, lariciresinol, pinoresin...
Table 16.2 Examples of lignan content (µg/100 g) of grain products.
Table 16.3 Gut bacterial transformation of SDG lignan to enterolignans by deglyc...
Table 16.4 A range of biological activities associated with the health propertie...
Chapter 17
Table 17.1 Composition of total phytosterols in whole grains (μg/g).
Table 17.2 Composition of free phytosterols in whole grains (μg/g).
Table 17.3 Composition of phytosteryl fatty acid esters in whole grains (μg/g).
Table 17.4 Composition of phytosteryl ferulates in whole grains (μg/g).
Table 17.5 Composition of phytosteryl glycosides and acylated phytosteryl glycos...
Chapter 18
Table 18.1 Content of phytic acid in major cereals, legumes, oilseeds, and nuts ...
Table 18.2 Biochemical properties of phytase from various organisms. Heat inacti...
List of Illustrations
Chapter 2
Figure 2.1 Evolutionary history of cultivated wheat. Wheat evolved by ...
Figure 2.2 Distribution of US wheat production, by market class.
Figure 2.3 Phenolic acid concentration of whole and white wheat. Values...
Figure 2.4 Ferulic acid and its free radical resonance structures.
Figure 2.5 Carotenoid concentration in wheats and corn. Values are mean...
Figure 2.6 Colonic tumor incidence in rodents fed diets containing whea...
Figure 2.7 Liver cholesterol concentration in rodents fed diets contain...
Chapter 3
Figure 3.1 Structures of bioactive components in oats.
Chapter 4
Figure 4.1 Whole grain rice processing. The whole grain brown rice cont...
Chapter 5
Figure 5.1 Structures of common phenolic compounds.
Figure 5.2 Structures of common phenolic acids found in corn: (a) benzo...
Figure 5.3 Structure of common anthocyanins found in purple, red, and b...
Figure 5.4 Structures of carotenoids found in corn: β‐carotene (a), α‐c...
Figure 5.5 Structures of tocopherols and tocotrienols found in corn.
Figure 5.6 Structures of common plant sterols found in corn.
Chapter 6
Figure 6.1 The barley seed longitudinal cross‐section shows the thick ...
Chapter 7
Figure 7.1Figure 7.1 Different types of rye breads.
Chapter 8
Figure 8.1 Documentation of amaranth in pre‐Hispanic and colonial codi...
Figure 8.2 Seeds of wild amaranths have a characteristic black color an...
Figure 8.3 Differences in panicle development between weedy and grain a...
Figure 8.4
A. cruentus
growing in a semi‐arid area with low water preci...
Figure 8.5 Scanning electron microscopy images of
A. hypochondriacus
se...
Figure 8.6 General structure of amaranth proglobulin 11S. (a) Monomer...
Figure 8.7 Electrophoretic profile of glutelins from different
Amaranth
...
Figure 8.8 Proposed mechanisms for amaranth bioactive peptides. Amarant...
Figure 8.9 Role of amaranth ACE inhibitors on hypertension. ACE, angiot...
Chapter 11
Figure 11.1 Chemical structure of AVA.
Figure 11.2 Biosynthesis of AVA.
Figure 11.3 Glucuronidation, sulfation, and methylation of AVA.
Figure 11.4 Absorption and elimination of oat AVA after acute oat cooki...
Figure 11.5 Chemical structure of dihydroavenanthramide D.
Figure 11.6 AVA protects against exercise‐induced muscle inflammation a...
Figure 11.7 AVA exerts antioxidant and antiinflammation effects in huma...
Figure 11.8 AVA inhibits the development of atherosclerosis in multiple...
Chapter 12
Figure 12.1 Fluorescence micrographs of cereal sections stained with Co...
Figure 12.2 Schematic diagram depicting the chemical structure of a por...
Figure 12.3 Plot of viscosity versus concentration of oat β‐glucan. The...
Figure 12.4 Fluorescence micrographs of processing effects on oat β‐glu...
Chapter 13
Figure 13.1 Chemical structure of five hydroxycinnamic acids (a) and f...
Chapter 14
Figure 14.1 Structures of the major dietary carotenoids.
Chapter 15
Figure 15.1 Basic structure of alkylresorcinols. The R group in cereal...
Figure 15.2 Liquid chromatographyfluorescence detector chromatograms of...
Figure 15.3 The range of alkylresorcinols in different cereals and cere...
Chapter 16
Figure 16.1 Chemical building blocks for lignans from whole grains. (a)...
Figure 16.2 Chemical structures of dietary plant lignans and enterolign...
Chapter 17
Figure 17.1 Chemical structures of free phytosterols, classified accor...
Figure 17.2 Examples of the chemical structures of phytosteryl conjugat...
Figure 17.3 Intestinal sterol absorption. ABCG5/G8: adenosine triphosph...
Chapter 18
Figure 18.1 Hypothesized beneficial effects of phytase on P and protein...
Guide
Cover
Table of Contents
Begin Reading
Pages
xv
xvi
xvii
xviii
1
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
209
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
269
270
271
272
273
274
275
276
277
278
279
280
281
282
284
285
286
287
288
289
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
Whole Grains and their Bioactives
Composition and Health
Edited by
Jodee Johnson
Associate Principal ScientistQuaker Oats Center of ExcellenceR&D NutritionSenior Scientist at PepsiCo R&D NutritionBarrington, IL, USA
Taylor C.Wallace
Principal & CEO at Think Healthy Group, Inc.Adjunct Professor, Department of Nutrition and Food StudiesGeorge Mason UniversityFairfax, Virginia, USA
Copyright
This edition first published 2019
© 2019 John Wiley & Sons Ltd
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions.
The right of Jodee Johnson and Taylor C. Wallace to be identified as the authors of this editorial material has been asserted in accordance with law.
Registered Offices
John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA
John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK
Editorial Office
The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK
For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com.
Wiley also publishes its books in a variety of electronic formats and by print‐on‐demand. Some content that appears in standard print versions of this book may not be available in other formats.
Limit of Liability/Disclaimer of Warranty
While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.
Library of Congress Cataloging‐in‐Publication Data
Names: Johnson, Jodee, editor. | Wallace, Taylor C., editor.
Title: Whole grains and their bioactives : composition and health / edited by
Jodee Johnson, Taylor C. Wallace.
Description: First edition. | Hoboken, NJ : Wiley, 2019. | Includes
bibliographical references and index. |
Identifiers: LCCN 2019003540 (print) | LCCN 2019004883 (ebook) | ISBN
9781119129462 (Adobe PDF) | ISBN 9781119129479 (ePub) | ISBN 9781119129455
(hardcover)
Subjects: | MESH: Whole Grains–chemistry | Phytochemicals
Classification: LCC QK861 (ebook) | LCC QK861 (print) | NLM WB 431 | DDC
572/.2–dc23
LC record available at https://lccn.loc.gov/2019003540
Cover Design: Wiley
Cover Image: © Madlen/Shutterstock
List of Contributors
James A. Anderson
Department of Agronomy and Plant Genetics
University of Minnesota
St Paul, MN
USA
Juan Antonio Giménez Bastida
Department of Clinical Pharmacology
Vanderbilt University School of Medicine
Nashville, TN
USA
Esau Bojórquez‐Velázquez
Molecular Biology Department
Instituto Potosino de Investigación Científica y Tecnológica A.C.
San Luis Potosí
Mexico
Klinsmann Carolo
Antioxidants Research Laboratory
Jean Mayer USDA Human Nutrition Research Center on Aging
Tufts University
Boston, MA
USA
Sérgio M. Costa
Antioxidants Research Laboratory
Jean Mayer USDA Human Nutrition Research Center on Aging
Tufts University
Boston, MA
USA
Christine E. Fastnaught
Phoenix Seed, Inc.
Fargo, ND
USA
Daniel D. Gallaher
Department of Food Science and Nutrition
University of Minnesota
St Paul, MN
USA
Ankit Goyal
Department of Dairy Technology
Mansinhbhai Institute of Dairy and Food Technology
Mehsana, Gujarat
India
Syed Irshaan
Department of Food Process Engineering
National Institute of Technology
Rourkela, Odisha
India
Li Li Ji
Laboratory of Physiological Hygiene and Exercise Science (LPHES)
School of Kinesiology
University of Minnesota‐Twin Cities
Minneapolis, MN
USA
Elizabeth J. Johnson
Friedman School of Nutrition and Science Policy
Tufts University
Boston, MA
USA
Jodee Johnson
Quaker Oats Center of Excellence
PepsiCo R&D Nutrition
Barrington, IL
USA
Kimia Kajbaf
Department of Animal and Veterinary Science
Aquaculture Research Institute
University of Idaho
Hagerman, ID
USA
Intelli Kaur
Department of Food Technology and Nutrition
Lovely Professional University
Phagwara
India
Indrikis Krams
Institute of Ecology, University of Tartu
Tartu
Estonia
Department of Zoology and Animal Ecology
Faculty of Biology
University of Latvia
Riga
Latvia
Vikas Kumar
Department of Food Technology and Nutrition
Lovely Professional University
Phagwara
India
Vikas Kumar
Department of Animal and Veterinary Science
Aquaculture Research Institute
University of Idaho
Hagerman, ID
USA
Department of Aquaculture and Fisheries
University of Arkansas at Pine Bluff
Pine Bluff, AR
USA
José Moisés Laparra Llopis
Group of Molecular Immunonutrition in Cancer
Madrid Institute for Advanced Studies in Food
Madrid
Spain
Tong Li
Department of Food Science
Cornell University
Ithaca, NY
USA
Rui Hai Liu
Department of Food Science
Cornell University
Ithaca, NY
USA
Laila Meija
Department of Sports and Nutrition
Rīga Stradiņš University
Pauls Stradiņš Clinical University Hospital
Riga
Latvia
S. Shea Miller
Ottawa Research and Development Centre
Agriculture and Agri‐Food Canada
Ottawa, ON
Canada
Nora Jean Nealon
Graduate Student
Department of Environmental and Radiological Health Sciences
College of Veterinary Medicine and Biomedical Sciences
Colorado State University
Fort Collins, CO
USA
Clarence W. (Walt) Newman
Plant & Soil Sciences Department
Montana State University
Bozeman, MT
USA
Rosemary K. Newman
Plant & Soil Sciences Department
Montana State University
Bozeman, MT
USA
Laura Nyström
Laboratory of Food Biochemistry
Institute of Food, Nutrition and Health
Zurich
Switzerland
C‐Y. Oliver Chen
Antioxidants Research Laboratory
Jean Mayer USDA Human Nutrition Research Center on Aging
Tufts University
Boston, MA
USA
Biofortis Research, Merieux NutriSciences
Addison, IL
USA
Ami Patel
Department of Dairy Microbiology
Mansinhbhai Institute of Dairy and Food Technology
Mehsana, Gujarat
India
Ana Paulina Barba de la Rosa
Molecular Biology Department
Instituto Potosino de Investigación Científica y Tecnológica A.C.
San Luis Potosí
Mexico
Alastair B. Ross
Department of Food and Nutrition Science
Department of Biology and Biological Engineering
Chalmers University of Technology
Gothenburg
Sweden
Elizabeth P. Ryan
Department of Environmental and Radiological Health Sciences
College of Veterinary Medicine and Biomedical Sciences
Colorado State University
Fort Collins, CO
USA
Shengmin Sang
Center for Excellence in Post‐Harvest Technologies
North Carolina A&T State University
Kannapolis, NC
USA
Siyuan Sheng
Department of Food Science
Cornell University
Ithaca, NY
USA
Manvesh Kumar Sihag
Department of Dairy Chemistry
Mansinhbhai Institute of Dairy and Food Technology
Mehsana, Gujarat
India
Amit K. Sinha
Department of Aquaculture and Fisheries
University of Arkansas at Pine Bluff
Pine Bluff, AR
USA
Yao Tang
Center for Excellence in Post‐Harvest Technologies
North Carolina A&T State University
Kannapolis, NC
USA
Beenu Tanwar
Department of Dairy Technology
Mansinhbhai Institute of Dairy and Food Technology
Mehsana, Gujarat
India
Susan Tosh
School of Nutrition Sciences
Associate Dean
Faculty of Health Sciences
University of Ottawa
ON
Canada
Aída Jimena Velarde‐Salcedo
Molecular Biology Department
Instituto Potosino de Investigación Científica y Tecnológica A.C.
San Luis Potosí
Mexico
Taylor C. Wallace
Think Healthy Group, Inc.
Department of Nutrition and Food Studies
George Mason University
Washington, DC
USA
Aaron Yerke
Center for Excellence in Post‐Harvest Technologies
North Carolina A&T State University
Kannapolis, NC
USA
Iman Zarei
Department of Environmental and Radiological Health Sciences
College of Veterinary Medicine and Biomedical Sciences
Colorado State University
Fort Collins, CO
USA
Tianou Zhang
Laboratory of Exercise and Sports Nutrition (LESN)
Department of Kinesiology, Health and Nutrition
The University of Texas at San Antonio
San Antonio, TX
USA
Dan Zhu
Laboratory of Food Biochemistry
Institute of Food, Nutrition and Health
Zurich
Switzerland
Henryk Zielinski
Department of Chemistry and Biodynamics of Food
Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences
Olsztyn
Poland
Part IIntroduction
1Introduction to Whole Grains and Human Health
Jodee Johnson1,2 and Taylor C. Wallace3,4
1PepsiCo R&D Nutrition, Barrington, Illinois, USA
2Quaker Oats Center of Excellence
3Think Healthy Group, Inc.
4Department of Nutrition and Food Studies, George Mason University, Washington, DC, USA
The existing scientific literature base indicates that the consumption of whole grains has a beneficial effect on maintaining human health over the lifespan. However, to date, most of the supporting evidence on disease prevention has been derived from observational studies. For example, in a 1992 study of 31 208 individuals in the Adventist Health Study cohort, Fraser et al. [1] found that there was a 44% reduction in nonfatal coronary heart disease (CHD) and an 11% reduced risk of fatal CHD for participants who consumed 100% whole‐wheat bread compared with those who ate white bread. In 1998, the Iowa Women's Health Study investigators also found an almost one‐third reduced risk of CHD death among individuals who consumed ≥1 serving of whole grains each day compared with those who did not consume whole‐grain products [2]. In 2005, the US Institute of Medicine (IOM) Food and Nutrition Board published dietary reference intakes for dietary fiber, which were largely based on whole grain studies. An adequate intake for total fiber was set at 38 and 25 g/day for young men and women, respectively, based on the intake level observed to protect against CHD [3]. It is important to expand the number of clinical intervention studies that assess the effect(s) of specific whole grains and whole grain products, as variations in their nutritional composition (e.g., dietary fiber, micronutrient and bioactive contents), effects on glycemic load, and health-promoting properties vary.
More recent data build on the existing evidence base and indicate that whole grain consumption is a good indicator of diet quality and nutrient intake [4,5]. Studies show that consumption of whole grains as part of a balanced diet decreases the incidence of CHD and many other chronic diseases (e.g., including, but not limited to, obesity, type 2 diabetes, and certain types of cancers) and promotes gastrointestinal tract regularity and function [6,7]. The potential health‐promoting effects of whole grains likely stem from synergies exhibited by the large array of essential nutrients, dietary fibers and bioactives present in the food matrix. The wide range of protective components in whole grains and potential mechanisms for protection have also been described in the scientific literature [ 6, 7].
The 2015–2020 Dietary Guidelines for Americans (DGAs) indicate that the US population's intake of total grains is close to target amounts; however, intakes do not meet recommendations for whole grains and exceed the limits for refined grains [8]. Average intakes of whole grains are far below recommended levels across all age and sex groups. Approximately 60% of whole grain intake in the US is from individual food items, such as breakfast cereals and oats, rather than mixed dishes. The DGAs recommend that consumers shift their diet such that they consume 50% of their grains as whole grains [8]. This recommendation is based on (i) literature demonstrating the contribution of whole grains in helping individuals meet nutrient recommendations and (ii) US Department of Agriculture (USDA) Evidence Analysis Library reports (used by the 2010 Dietary Guidelines Advisory Committee to inform the 2010 DGAs [9]) showing effects of whole grain consumption on both cardiovascular disease (CVD) and type 2 diabetes. The USDA Evidence Analysis Library reports concluded that (i) there is a moderate body of evidence from large prospective cohort studies showing that whole grain intake is associated with an approximately 21% lower risk of CVD and (ii) limited evidence supports an association between whole grain intake and an approximately 26% lower risk of type 2 diabetes [10].
This chapter seeks to review the basics of whole grains, their bioactives, and related potential health‐promoting properties.
1.1 History of Whole Grains
With the advent of agriculture >10 000 years ago, whole grains became a central part of the human diet [11]. The majority of the world's population has relied on whole grains as a major component of the diet for at least the last 4000 years. Refined grains were introduced to society within the last 100 years. Prior to the introduction of technologies used to process refined grains, gristmills were used to grind grains and produce limited amounts of flour. Gristmills were inefficient in completely separating the bran and germ from the white endosperm. In 1873, the roller mill was introduced; its widespread use was applied to satisfy increasing consumer demand for refined grain products. Introduction of the roller mill was a significant factor in the sharp decline in whole grain consumption observed from 1873 through the 1970s [11].
Health benefits of whole grains have been postulated since the fourth century, when Hippocrates coined the famous proverb “Let food be thy medicine and thy medicine be food.” In that era, whole cereal grains (particularly barley and wheat) were the principal food throughout the Mediterranean. For thousands of years, humans consumed these foods in whole form (e.g., whole wheat berries), in cracked grains (e.g., bulgur and couscous), and in bread or baked goods. Hippocrates' healing diet consisted of eating whole grain barley, somewhat softly prepared, at every meal every day for a period of approximately 10 days. This practice became a widespread home remedy in early Western medicine.
In the last 200 years, whole grain intake has been traditionally recommended to prevent constipation. The “fiber hypothesis” was first published in 1972, suggesting that large amounts of unrefined plant foods, especially those starchy foods rich in dietary fiber, may offer protection against type 2 diabetes and diseases of the large bowel [12,13]. The inclusion of whole grains as part of a healthful diet has been a component of the DGAs since the first edition published by the USDA and the Department of Health and Human Services in 1980 [14].
1.2 Who Consumes Whole Grains?
Current dietary guidelines encourage consumers to increase intakes of both dietary fiber and whole grains. Since 2000, the DGAs have recommended that individuals consume at least 3 oz‐equivalents of whole grain daily and that at least half of all total grains consumed should be whole [8]. Data from the 2009–2010 National Health and Nutrition Examination Survey (NHANES) show that whole grain intakes are approximately 0.57 oz‐equivalents/day for children and 0.82 oz‐equivalents/day for adults. Total dietary fiber intakes in the US are directly associated with whole grain intake [15]. Only about one‐third of Americans aged >12 years meet the grain intake recommendation, and only 4% meet the current whole grain intake recommendations. Mean intakes of whole grains fall well below (less than one‐third) intake recommendations for all age groups. Despite increased public health messaging and the growing number and availability of whole grain‐containing products, data show that there have been no significant changes in whole grain intakes for any age group over the last decade [16]. Major sources of whole grains for the US population include ready‐to‐eat cereals, yeast bread/rolls, hot cereal, and popcorn [ 15, 16]. Whole grain intakes are shown to be highest at breakfast (53%) [ 16,17], which is likely driven by ready‐to‐eat cereal intake. Intake at breakfast contributes 44%, 39%, and 53% of the total intakes of whole grains for children/adolescents, adults aged 19–50 years, and adults aged >51 years, respectively [17]. More than 19% of whole grain consumption is obtained through snack foods.
1.3 What are Whole Grains?
According to the American Association for Cereal Chemistry International [18], whole grains consist of:
intact, ground, cracked, or flaked fruit of the grain whose principal components, the starchy endosperm, germ, and bran, are present in the same relative proportions as they exist in the intact grain.
Whole grains can be present as a complete food (e.g., oatmeal or brown rice) or used as an ingredient in food (e.g., whole‐wheat flour in bread). What constitutes a whole grain food is yet to be defined, which creates unique challenges for manufacturers, researchers, regulatory agencies, and consumers [19]. Foods that are only partially composed of whole grains can be problematic when assessing population intakes, since relative proportions may be proprietary information to the manufacturer. US Food and Drug Administration (FDA) regulations state that in order for a manufacturer to use the whole grain health claim on a product label, the food must contain at least 51% whole grain ingredients by weight per reference amount customarily consumed (RACC). Whole wheat contains 11 g of dietary fiber/100 g; thus, the qualifying amount of dietary fiber required for a food to bear the prospective claim can be determined by the following formula: 11 g × 51% × RACC/100 [20]. The most common consumed grains include wheat, oats, rice, corn, and rye. Wheat accounts for about 70–75% of grain consumption in the United States.
Although the term whole grain has been at least somewhat defined, what constitutes a “whole grain food” is less clear; a definition has not yet been developed and adopted for use by the USDA, FDA, Health Canada, or European Commission. In the United States, the USDA estimates a standard grain food serving size to be 1 oz‐equivalent, whereas the FDA estimates this value to be approximately 30 g [21]. Experts agree that a specific definition for whole grain foods that incorporates a specific amount of whole grains per 30 g serving is needed [19].
Types of whole grains include whole wheat, whole oats/oatmeal, whole grain cornmeal, popcorn, brown rice, whole rye, whole grain barley, wild rice, buckwheat, triticale, bulgur (cracked wheat), millet, quinoa, and sorghum. Other less common whole grains include amaranth, emmer, farro, grano (lightly pearled wheat), spelt, and wheat berries.
1.4 Components of Whole Grains
All grains have a bark‐like protective hull, which encases the germ, endosperm, and bran. The germ contains the plant embryo. The endosperm, composed of approximately 50–75% starch, is the largest component of the whole grain and is the major energy supply for the embryo during germination. Surrounding the germ and endosperm is a protective covering known as the bran, which provides a barrier to damage from sunlight, pests, water, and so forth. Most micronutrients (i.e., vitamins and minerals) are located in the germ and bran; the endosperm contains very few micronutrients. The germ is relatively small and accounts for only approximately 4–5% of the dry weight of most grains such as wheat, oats, and barley. By contrast, the germ in corn contributes a much higher proportion. Whole grains are typically high in B vitamins (thiamin, niacin, riboflavin, and pantothenic acid), minerals (calcium, magnesium, potassium, phosphorus, sodium, and iron), and dietary fibers. Dietary bioactives are also largely located in the bran and germ. Whole grains provide unique and efficacious profiles of dietary bioactive compounds (e.g., avenanthramides in oats) that have been suggested to influence human health beyond basic nutrition. In most developed countries, whole grains are subjected to processing, which in turn can affect the composition, stability, bioavailability, and health‐promoting properties of the bioactives present in any given food matrix.
Refined grains are defined as grains that have been milled, a process that removes the bran and germ. Milling gives grains a finer texture and improves their shelf‐life but it also removes most of their dietary fiber, iron, and many B vitamins. Examples of refined grain products include white flour, “degermed” corn meal, white bread, and white rice. As much as 75% of the dietary bioactives found in whole grains are lost during the refining process. Compared with refined grains, most whole grains provide higher amounts of protein, dietary fiber, and more than a dozen vitamins and minerals. Since the early 1940s, US regulations have mandated that refined flour must be enriched with some B vitamins (thiamin, riboflavin, and niacin) and iron [22]. In 1996, the FDA mandated that enriched grain products be fortified with folic acid to help women of childbearing age reduce the risk of neural tube defects during pregnancy [23].
1.5 Whole Grain Bioactives
Many studies suggest that the health‐promoting effects of whole grains extend beyond their dietary fiber content, with studies showing that even after controlling for fiber intake, the beneficial effects of whole grains and heart disease remain, at least to some extent. Although the dietary fiber and other essential nutrients present in whole grains likely account for a significant portion of the postulated health effects, dietary bioactives most certainly play a synergistic role in health maintenance and disease prevention. The National Institutes of Health Office of Dietary Supplements [24] defined dietary bioactives as “compounds that are constituents in foods and dietary supplements, other than those needed to meet basic human nutritional needs, which are responsible for changes in health status.” Most of the health‐promoting dietary bioactives present in whole grains are found in the germ and bran fraction of the grain kernel and include, but are not limited to, phenolic compounds, phytosterols, tocols, dietary fibers (mainly β‐glucans), lignans, alkylresorcinols, phytic acid, γ‐oryzanols, avenanthramides, cinnamic acid, ferulic acid, inositols, and betaine.
Although much research has focused on individual components of whole grains (e.g., specific dietary bioactives or fiber), epidemiological evidence suggests that the whole grain food offers the greatest protection against chronic disease compared to its individual components alone. Some dietary bioactives are specific to certain cereal grains, such as γ‐oryzanol in rice, β‐glucans in oats and barley, avenanthramides and saponins in oats, and alkylresorcinol in rye, although these compounds are also present in relatively lower amounts in other cereals such as wheat.
1.6 Health‐Promoting Effects of Whole Grains
Although evidence continues to emerge, observational studies consistently suggest that the consumption of 2–3 servings of whole grains daily is associated with beneficial health effects (primarily a reduced risk of CVD and type 2 diabetes). Under the provisions of the FDA Modernization Act 1997, a manufacturer may submit to the FDA a notification of a health claim based on an authoritative statement from an appropriate federal agency or the National Academy of Sciences (NAS) [20]. On March 10, 1999, General Mills Inc. submitted to the US FDA a notification containing a prospective claim about the relationship between whole grain foods and heart disease and certain cancers. The notification cited the following from the Executive Summary of the NAS report, Diet and Health: Implications for Reducing Chronic Disease Risk, as an authoritative statement:
Diets high in plant foods – i.e., fruits, vegetables, legumes, and whole grain cereals – are associated with a lower occurrence of CHD and cancers of the lung, colon, esophagus, and stomach. [21, p. 8]
Whole grains are rich sources of vitamins, minerals, dietary fiber, lignins, β‐glucans, inulin, numerous phytochemicals, phytosterols, phytin, and sphingolipids [25–28]. Most bioactives in whole grains are derived from their unique bran and germ structure [25]. Current scientific research indicates that the different types of dietary bioactives present in whole grains (and other plant foods) work synergistically to promote health [26]. Plants synthesize many dietary bioactive compounds in response to environmental factors including, but not limited to, ultraviolet light, frost hardiness, and pathogens [29]. Once consumed, bioactives may retain their protective character and work as antioxidants or antiinflammatory agents in vivo [26]. The dietary bioactives responsible for health benefits associated with whole grains may also complement those contained in fruits and vegetables when consumed together [ 25– 28].
Although the totality of research suggests effects of whole grain bioactives on numerous chronic health outcomes, it is important to note that research on the efficacy and biological potential of many whole grain bioactives is limited to small short‐term clinical trials and to population studies, which cannot be used to determine causality. Additional long‐term clinical research is needed to confirm the effects of whole grain bioactives on established biological mechanisms and on both surrogate and clinical endpoints of chronic disease. Examples of dietary bioactives found in whole grains and their postulated physiological benefits are described below and summarized in Table 1.1.
Table 1.1 Examples of dietary bioactives found in whole grains and their postulated physiological effects.
Source: Adapted with permission from Slavin et al. [30].
Dietary bioactive
Physiological function
Phenolics: phenolic acids and flavonoids (e.g., avenanthramides, ferulic acid, vanillic acid, and caffeic acid)
Antioxidant
Antiinflammation
Blood cholesterol and glucose modulation
Carotenoids (e.g., lutein, zeaxanthin, β‐cryptoxanthin, β‐carotene, and α‐carotene)
Provitamin
Antioxidant
Macular‐retinal composition/function
Vitamin E (tocopherols and tocotrienols)
Antioxidant
Maintenance of cellular membrane integrity
Immune function modulation
DNA repair
γ‐Oryzanol
Antioxidant
Blood cholesterol modulation
Plant sterols and stanols
Blood cholesterol modulation through inhibited absorption and increased excretion
Cereal fiber
Lower risk of cardiovascular disease, diabetes, and certain cancers
Body weight regulation
β‐Glucan
Blood cholesterol and glucose modulation
Immune function modulation
Resistant starches, inulin, and oligosaccharides
Probiotic (modulation of gut microbiota)
Improve digestive health (fecal bulk, transit time, colon health), improve immune function, lower inflammation
Lower risk of gastrointestinal cancers
Blood glucose modulation
Modulation of fat metabolism
Energy intake regulation
Lignans
Antioxidant
Phytoestrogenic effects
Phytic acid
Antioxidant
Metal ion chelators
Enzyme inhibitors (e.g., amylase and protease inhibitors)
Blood cholesterol and glucose modulation
Lower risk of certain cancers (e.g., breast and colon)
1.6.1 Body Weight Regulation
Although whole grains contain similar energy (i.e., kilocalories) to refined grains, there is significant scientific evidence that consumption of whole grains may lead to reduced body fat and weight. Data from observational studies consistently indicate that consuming approximately three servings of whole grains per day is associated with a lower body mass index (BMI), smaller waist circumference, smaller waist‐to‐hip ratio, and lower abdominal, subcutaneous, and visceral adipose tissue volume [31,32]. Prospective cohort studies also suggest that weight gain and increases in abdominal obesity are lower among individuals who consume higher amounts of whole grains [33,34]. Data from the 1999–2004 NHANES (n = 13 276) suggest an association between consuming whole grains and having lower body weight, BMI, and waist circumference across all age groups [35]. A 2012 systematic review of randomized controlled trials (RCTs) and prospective cohort studies showed that individuals who consumed whole grains (compared to nonconsumers) often experienced less weight gain over 8–12 years of follow‐up [32]. Consistent with this, a 2013 systematic review of small RCTs showed that consuming whole grains may decrease body fat percentage, waist circumference, and BMI [36]. Emerging evidence from clinical studies indicates that whole grain consumption may alter body fat distribution, independent of changes in weight, although the mechanism of action is yet to be identified [31].
Proceedings of a American Society for Nutrition‐sponsored symposium on health benefits associated with whole grains noted that 14 human intervention studies showed that consuming higher amounts of whole grains was associated with lower BMI, three studies showed that consuming whole grains was associated with smaller waist circumference, and one study found that consuming whole grains was associated with lower abdominal fat in a dose‐dependent manner [37].
Whole grains are also a major source of dietary fiber in the US diet. The IOM recommends that all individuals aged <70 years consume 14 g of total fibers/1000 kcal daily to ensure optimal health [3]. Whole grains contain approximately 2–3 g of soluble fibers per serving compared with approximately 1–2 g per serving of fresh fruit [8]. The 2005 DGAs recommended, for the first time, that “consuming at least 3 or more ounce‐equivalents of whole grains per day can reduce the risk of several chronic diseases and may help with weight maintenance” [38]. The eighth edition of the DGAs published in 2015 continues to recommend that individuals strive to limit intake of refined grains and to consume at least half of all grains as whole grains [8]. This recommendation is based on food‐modeling patterns showing that whole grain intake contributes to increased intakes of several essential vitamins, minerals, and different types of fibers, but it almost certainly considers other dietary bioactives.
The soluble fibers in whole grains are considered a major component responsible for their effects on weight management. Soluble fibers bind with water to form a gel solution in the digestive tract. The gel‐like fibers delay gastric emptying, reduce intestinal transit speed, and decrease nutrient absorption. Delayed gastric emptying has satiating effects and thus may help to reduce appetite. Another possible mechanism as to why intake of whole grains may benefit weight management is their noted effects on the gastrointestinal microflora. It has been widely shown that changes in the gut microbiome due to high fermentable fiber intake may affect metabolism and thus influence body weight regulation. The products of fiber fermentation may have the biological potential to help regulate insulin and gastrointestinal hormone secretion in the human body. Fermentable fibers in whole grains can be broken down by the gastrointestinal microflora to produce short‐chain fatty acids (SCFAs). Among these SCFA products, propionate and acetate have been suggested to increase satiety [39–41]. SCFAs such as acetate, propionate, and butyrate are absorbed in the colon, may stimulate several metabolic pathways in the brain. Higher acetate levels in the brain typically result in acute appetite suppression, at least in animal models [40].
1.6.2 Gastrointestinal Tract Health
Consumption of whole grains has been widely shown to benefit gut health and gastrointestinal regularity. Fermentable and unfermentable fibers help protect the gastrointestinal tract in many ways. The insoluble and unfermentable fiber content in whole grains may help prevent and relieve constipation. These fibers cannot be digested or fermented in the human digestive tract due to their chemical bonds. They instead retain their unique structure in the human digestive tract and increase fecal bulk, leading to improved gastrointestinal transit. Fermentable fibers, although also nondigestible, can be fermented by bacteria in the colon, and their fermentation products can play specific roles in maintaining immune system health. Nonstarch polysaccharides, oligosaccharides, and resistant starches act as the primary dietary substrates derived from whole grains that are fermented by bacteria in the gastrointestinal tract [27,42,43]. Many fermentable fibers promote barrier building and function in the gastrointestinal tract, while also helping to improve blood flow in the colon and protect the gastrointestinal tract from harmful toxins and pathogens. Their fermentation products (mostly SCFAs), meanwhile, may help to reduce growth of common pathogens and have inhibitory effects on colonic neuromuscular activity, diarrhea, and oncogenesis in the gut [44]. The principal products of this fermentation are SCFAs such as acetate, propionate, and butyrate. Numerous clinical trials have shown that daily consumption of whole grains such as wheat, corn, and oats has a prebiotic effect on the composition of the gut microflora, likely due in part to the production of SCFAs [45]. Butyrate in particular has been shown to promote crypt cell growth; crypt cells located at the lumen are critical for nutrient absorption and act as a physical barrier [ 39, 40].
Other dietary bioactives found in whole grains, such as phenolic acids, flavonoids, carotenoids, and lignans, may also influence gastrointestinal health and function [27] by performing antioxidant, antiinflammatory, and other beneficial physiological functions. Flavonoids such as anthocyanins have been extensively studied for their potential to inhibit cancers of the colon [46]. Thus, whole grains help to maintain the gastrointestinal tract and protect it against chronic disease by providing more than just fiber.
1.6.3 Type 2 Diabetes
Consumption of recommended intakes of whole grains has been associated with a reduced risk of type 2 diabetes, particularly among participants in prospective cohort studies. A 2012 systematic review of prospective cohort studies found that individuals who consumed 48–80 g of whole grains per day had a 26% reduced risk of type 2 diabetes [32]. This is equivalent to 3–5 servings of whole grains per day. A prominent cohort study with 10‐year follow‐up showed whole grain consumption to be associated with a 35% decreased risk of type 2 diabetes [47].
Among RCTs, supplemental psyllium fiber has been shown to decrease blood glucose levels in patients with type 2 diabetes and/or metabolic syndrome [48]. β‐Glucans show a very similar effect in clinical studies and consistently reduce initial glycemic response and lower postprandial glucose peak value [49]. Improvement in intermediate markers of type 2 diabetes, including postprandial insulin and glucose response, may be more evident among individuals who are overweight or have type 2 diabetes. Investigators observed in a small clinical trial that overweight and obese individuals had a 10% lower fasting insulin response and decreased insulin resistance after six‐week consumption of a whole grain diet compared with a refined grain diet [50].
Further research is needed to better understand the mechanism of action of whole grains on type 2 diabetes. Not all whole grains are equal, and some have unique physical structures that contribute to their beneficial effects on type 2 diabetes. For instance, consumption of rye bread has consistently been associated with larger improvements in postprandial insulin response among participants in small RCTs [51,52]. After baking, rye bread is firmer than normal wheat bread. The amylose in rye forms a hard coat outside the starch granule, lowering the starch's rate of hydrolysis [52]. The polyphenols in rye have also been credited with its ability to modulate insulin resistance [53]. Bioactives and prebiotics present in whole grains may also play a substantial role in modulating glycemic response. SCFAs have been hypothesized to affect insulin sensitivity by stimulating glucagon‐like peptide 1 secretion in cells [39]. Similarly, SCFAs may influence hepatic glucose oxidation and decrease fatty acid release and insulin clearance, thereby improving insulin sensitivity [47].
It is widely known that whole grains are a source of soluble fibers that can form gels within the gastrointestinal tract, which have been shown to trap nutrients and slow (or inhibit) their absorption. This in turn may modulate glucose response and secretion of other gastrointestinal hormones. Many polyphenols, particularly the larger molecular weight substances, have also been known to bind nutrients and inhibit their absorption.
The FDA previously authorized a health claim that states “diets rich in whole grain foods and other plant foods and low in total fat, saturated fat, and cholesterol, may help reduce the risk of heart disease and certain cancers” based on significant scientific agreement between clinical intervention and prospective cohort studies. Although this claim is weighted heavily on the dietary fiber composition of whole grains, the FDA most certainly considered the postulated effects of the many dietary bioactive compounds present in the food matrix.
1.6.4 Cardiovascular Diseases
Cardiovascular diseases accounted for approximately 31% of global deaths in 2012 and continue to be the leading cause of death worldwide [54]. A 2016 systematic review of prospective cohort studies showed that a 90 g/day increase in whole grain intake (90 g is equivalent to three servings) was associated with a 19% reduction in CHD and a 12% reduction in CVD [55]. Epidemiological and clinical intervention studies consistently suggest that consumption of whole grains may decrease the risk of CVDs, likely due to their ability to lower both low‐density lipoprotein (LDL) cholesterol and blood pressure [ 26, 31, 3256–58]. Prospective cohort studies have consistently shown that consumption of whole grains has an inverse association with and a lower risk of death from ischemic heart disease, CHD, incident heart failure, hypertension, and coronary artery intima thickness and diameter (a measure of atherosclerosis) [ 31, 32 56– 58]. The CVD‐preventive effects of whole grains are greater than those from cereal fiber alone or fiber from fruit and vegetable intake.
Several mechanisms have been proposed for why whole grains reduce the risk of CVDs. The evidence surrounding the efficacy of oat and barley β‐glucans in lowering LDL cholesterol is particularly strong. β‐Glucans have been known to increase cholesterol and bile acid excretion in the feces [3]. Other mechanisms include the ability of certain dietary bioactives such as polyphenols to exert antioxidant and antiinflammatory properties, as well as fermentation of whole grain polysaccharides in the large bowel with resulting SCFA production, which can inhibit cholesterol synthesis [ 27, 28, 32]. Whole grain consumption has been suggested to lower C‐reactive protein levels in vivo [37]. It is also worth noting again that gel‐forming soluble fibers can trap lipids and decrease their absorption into the bloodstream.
1.6.5 Cancer
Despite the well‐documented effects of whole grains, little is known about their influence on cancer mortality. A recent dose–response metaanalysis of clinical trials and prospective cohort studies found that incremental intake of 50 g/day whole grains resulted in an 18% reduction in cancer mortality (hazard ratio [HR] 0.82; 95% confidence interval [CI] 0.69–0.96) [59]. A similar metaanalysis of prospective cohort studies found consistent results, showing a 12% reduction in cancer mortality (HR 0.88; 95% CI 0.83–0.94) [60]. Consuming three or more servings of whole grains daily also seems to reduce one's risk of total cancer by approximately 15% (HR 0.85; CI 95% 0.80–0.91), as shown in a separate metaanalysis of prospective cohort studies [61]. Adiposity and type 2 diabetes are known clinical risk factors for development of cancer; however, the above metaanalyses all adjusted for these risk factors, indicating that the mechanisms involved exceed those basic effects on body composition and insulin sensitivity.
Colorectal cancers are the third most common cancer type in men and the second most common cancer type in women. Based on significant scientific evidence from clinical intervention and prospective cohort studies, the FDA authorized a health claim around whole grain intake and cancer. Whole grain consumption seems to have strongest inverse relationships with development of gastrointestinal cancers, certain hormone‐related cancers, and pancreatic cancer [62,63]. A recent joint report from the World Cancer Research Fund (WCRF) and American Institute for Cancer Research (AICR) found a 17% decrease in colorectal cancer risk for each 90 g/day (equivalent to three servings/day) increase in whole grains. No significant effects were found in relation to risk of rectal cancer, which could be explained by the lower number of cases reported in studies included in the metaanalysis [64].
In contrast to refined grains, that only retain the endosperm, the germ and bran of whole grains are rich sources of various substances with anticancer properties, including antioxidants, fiber, and other dietary bioactives. More than 30 types of bioactive compounds present in whole grains have been shown to have the potential to reduce the risk of certain types of cancers [27]. A circulating biomarker of whole grain intake, alkylresorcinols, has been developed, as they reside exclusively in the bran part of wheat and rye, are not affected by food processing, and can be measured in the blood plasma with moderate reproducibility and validity. Increased plasma alkylresorcinol has been inversely linked to decreases in colorectal cancers [65,66].
1.7 Conclusion
Overall, there is convincing scientific evidence that support the current US DGAs, which recommends at least three servings/day of whole grain intake. Biomarkers of whole grain intake are greatly needed as many studies rely on self‐report and inconsistent quantities of whole grains present in mixed dishes. It is our hope that the subsequent chapters will summarize and give perspective to the effects of whole grains and their bioactives in relation to a number of chronic disease states.
References
1 Fraser, G.E., Sabate, J., Beeson, W.L., and Strahan, T.M. (1992). A possible protective effect of nut consumption on risk of coronary heart disease. The Adventist Health Study.
Arch. Intern. Med.
152 (7): 1416–1424.
2 Jacobs, D.R. Jr. Meyer, K.A., Kushi, L.H., and Folsom, A.R. (1998). Whole‐grain intake may reduce the risk of ischemic heart disease death in postmenopausal women: the Iowa Women's Health Study.
Am. J. Clin. Nutr.
68 (2): 248–257.
3 Institute of Medicine Food and Nutrition Board (2005).
Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids
. Washington, DC: National Academies Press.
