Digestion and Absorption of the Macronutrients

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4 Overview of Digestion and Absorption 75

Patrick Tso, Ph.D., and Karen D. Crissinger, M.D., Ph.D.

Digestion and Absorption in the Gastrointestinal Tract 76

The Mouth 76

The Stomach 77

The Small Intestine 78

Metabolism of Nutrients in the Enterocytes 85

Transport of Nutrients in the Circulation 85

Regulation of Digestion and Absorption 86

Developmental Aspects of Gastrointestinal Physiology 88

The Large Intestine and the Role of Colonic Bacteria 89

5 Digestion and Absorption of Carbohydrate 91

Carbohydrate Components of the Human Diet 92

Sites and Mechanisms of Digestion of Carbohydrates 93

Absorption of Hexoses by the Enterocyte: Mechanisms and Regulation 97

Factors Influencing Carbohydrate Assimilation 101

6 Digestion and Absorption of Protein 107

Digestion of Protein in the Gastrointestinal Tract 108 The Gastric Phase: Denaturation and Initial

Hydrolysis of Proteins 108 Small Intestinal Luminal Phase: Activation and

Action of Pancreatic Proteolytic Enyzmes 110 Small Intestinal Mucosal Phase: Brush Border and Cytosolic Peptidases 112

Absorption of Free Amino Acids and Small Peptides 113 Metabolism of Amino Acids in Intestinal

Epithelial Cells 120

Use of Free Amino Acids and Peptides for Therapeutic

Oral Rehydration 121

Uptake of Protein Macromolecules and

Immune Response 121

7 Digestion and Absorption of Lipids 125

Patrick Tso, Ph.D., and Karen D. Crissinger, M.D., Ph.D.

Dietary Lipids 126

Luminal Digestion of Lipids 126

Uptake of Lipid Digestion Products by the Enterocytes 128

Intracellular Metabolism of Absorbed Lipids 130

Assembly of Intestinal Lipoproteins 133 Factors Affecting Formation and Secretion of Chylomicrons 135

Disorders of Intestinal Lipid Absorption 137

Intestinal Lipid Absorption and Mucosal Injury 138

Regional Differences in Intestinal Lipid Absorption 139

Portal Transport of Long-Chain Fatty Acids 139

Satiety Effects of Fat Feeding 140

8 Dietary Fiber 143

Joanne H. Lupton, Ph.D., and Nancy D. Turner, Ph.D., C.N.S.

Definition of Fiber 144

Major Physiological Effects of Fibers and Structure/Function

Relationships 146

Recommendations for Fiber Intake 152


Metabolism of the Macronutrients

9 Carbohydrate Metabolism—Synthesis and Oxidation 158

Overview of Carbohydrate Metabolism 159

Transport of Glucose Across Cell Membranes 160

Glycolysis 162

Gluconeogenesis 170

Regulation of Glycolysis and Gluconeogenesis 175 Regulation of the Expression of Glycolytic and Gluconeogenic Genes 183

Glycogen Metabolism 190

Regulation of Glycogenesis and Glycogenolysis 192

Pyruvate Dehydrogenase Complex and Citric Acid Cycle 198

Electron Transport and Oxidative Phosphorylation 202

Other Pathways of Carbohydrate Metabolism 205

10 Protein Synthesis and Degradation 211

Margaret A. McNurlan, Ph.D., and Peter J. Garlick, Ph.D.

Essentiality of Protein 212

Dynamic Protein Metabolism 213

Measurement of Protein Synthesis and Degradation 215

Protein Turnover and Adaptation 219 Regulation of Protein Synthesis and Degradation at the Molecular Level 219

Regulation of Protein Metabolism 224

11 Amino Acid Metabolism 233

Martha H. Stipanuk, Ph.D., and Malcolm Watford, D.Phil.

Overview of Amino acid Metabolism 234

Transport of Amino Acids 236 Reactions Involved in the Transfer, Release, and Incorporation of Nitrogen 237

Metabolism of the Carbon Chains of Amino Acids 240

Synthesis of Dispensable Amino Acids 245

Metabolism of Specific Amino Acids 245

Nitrogen Excretion 281

12 Protein and Amino Acid Requirements 287

The Physiological Basis of Protein and Amino Acid Requirements 288

Food Proteins and Protein Quality 291 Assessment of Requirements for Dietary Protein or

Amino Acids 296

Factors that Affect Amino Acid Requirements 302

13 Lipid Metabolism—Synthesis and Oxidation 305

Biological Roles for Lipids 306

Contents ♦ ♦ ♦


Synthesis of Long-Chain Fatty Acids from Acetyl CoA


Synthesis of Fatty Acids Other than Pa Imitate


Synthesis and Storage of Triacylglycerol


Mobilization of Stored Triacyglycerol


Oxidation of Fatty Acids


Formation of Ketone Bodies from Acetyl CoA in

the Liver as a Fuel for Extrahepatic Tissues


Synthesis of Cholesterol from Acetyl CoA Units


Phosphatidate and Diacylglycerol as Precursors of Phospholipids


Sphingolipids as Structural and Signaling Molecules


Lipoprotein Synthesis, Transport, and Metabolism


Christopher J. Fielding, Ph.D.

Classification of Plasma Lipoproteins


Synthesis and Secretion of Plasma Lipoproteins


Clearance of Triacylglycerol in Chylomicrons and VLDL

by Lipoprotein Lipase


Role of HDL and Lecithin:Cholesterol Acyltransferase

in Plasma Cholesterol Metabolism


Removal of Plasma Lipoproteins by Receptor-Mediated Processes


Postprandial Lipoprotein Metabolism


Chronic Effects of Dietary Lipids on Plasma Lipoproteins

and Lipid Metabolism


Lipid Metabolism: Essential Fatty Acids


Arthur A. Spector, M.D.

Historical Perspective


Structure of Polyunsaturated Fatty Acids


Polyunsaturated Fatty Acid Synthesis

in Mammalian Tissues


Essential Fatty Acids in Plasma


Essential Fatty Acid Deficiency


Polyunsaturated Fatty Acid Function


Lipid Peroxidation


Effects on Plasma Cholesterol and Lipoproteins

Effects on Plasma Cholesterol and Lipoproteins

Regulation of Gene Expression 381

16 Regulation of Fuel Utilization 384

Malcolm Watford, D.Phil., and Alan G. Goodridge, Ph.D.

Fuels 385

The Metabolic Fate of Macronutrients 388

Hormonal Signals for Regulation of Fuel Utilization 395

Regulation and Control of Fuel Utilization 401

UNIT IV Energy

17 Cellular and Whole-Animal Energetics 411

Adamandia D. Kriketos, Ph.D., John C. Peters, Ph.D., and James 0. Hill, Ph.D.

Metabolic Sources of Heat Production 412

Oxidative Phosphorylation 413

Oxidation of Fuel Molecules 414

Efficiency of Energy Conservation from Fuel Oxidation 416

Substrate Cycling 417

Measurement of Energy Expenditure 417

Components of Energy Expenditure 419

Determinants of Resting Metabolic Rate 421

18 Control of Energy Balance 425

John C. Peters, Ph.D., Adamandia D. Kriketos, Ph.D., and James O. Hill, Ph.D.

Basic Concepts 426

Control of Energy Intake 430

Control of Energy Expenditure 434

Integration of Energy Intake and Expenditure 436

19 Disturbances of Energy Balance 439

James O. Hill, Ph.D., Adamandia D. Kriketos, Ph.D., and John C. Peters, Ph.D.


Definition 440

Prevalence of Obesity 440

Health Consequences of Obesity 442

Factors Involved in Development of Obesity 443

Obesity Management 446

Methods of Obesity Treatment 447

Why is it Difficult to Maintain a Reduced Body Weight? 449 Starvation

Occurrence, Definition, and Historical Perspective 450 Effects on Energy Balance, Fuel Metabolism, and Body Composition 451

Adaptation to Prolonged Starvation 451 Protein Energy Malnutrition Effects on Energy Balance, Fuel Metabolism, and Body Composition 452

Adaptation to Chronic Undernutrition 452

Long-Term Effects of Protein Energy Malnutrition 452


The Vitamins

20 Niacin, Riboflavin, and Thiamin 458

Donald B. McCormick, Ph.D.


Niacin and Pyridine Nucleotide Coenzyme Structure and Nomenclature 459

Sources, Digestion, and Absorption 460

Transport and Conversion of Niacin to Coenzymes 463

Niacin Catabolism and Excretion 463

Functions of Pyridine Nucleotide Coenzymes in Metabolism 464

Noncoenzymic Functions of Niacin 466

Niacin Deficiency 466

Biochemical Assessment of Niacin Nutriture 467

Niacin Requirements 468 Riboflavin

Riboflavin and Flavocoenzyme Structure and Nomenclature 468

Sources, Digestion, and Absorption 469

Transport and Conversion of Riboflavin to Coenzymes 471

Riboflavin Catabolism and Excretion 472

Functions of Flavocoenzymes in Metabolism 472

Riboflavin Deficiency 473

Biochemical Assessment of Riboflavin Nutriture 475

Riboflavin Requirements 475 Thiamin

Thiamin and Thiamin Coenzyme Structure and Nomenclature 475

Sources, Digestion, and Absorption 476

Transport and Conversion of Thiamin to Coenzyme 476

Thiamin Catabolism and Excretion 477

Functions of Coenzymic Thiamin in Metabolism 477

Thiamin Deficiency 479

Biochemical Assessment of Thiamin Nutriture 480

Thiamin Requirements 480

21 Folic Acid, Vitamin B12, and Vitamin B6 483

Barry Shane, Ph.D. Folate

Chemistry of Folate 484

Sources of Folate 485

Bioavailability and Absorption of Folate 485

Transport and Tissue Accumulation of Folate 486

Intracellular Metabolism and Turnover of Folate 487

Metabolic Functions of Folate 488

Folate Deficiency: Symptoms and Metabolic Bases 495

Folate Requirements 500

Folate Toxicity 500 Vitamin Bq2

Chemistry of Vitamin B12 501

Sources of Vitamin B12 501

Bioavailability and Absorption of Vitamin B12 502

Transport of Vitamin B12 503

Intracellular Metabolism of Vitamin B12 504

Metabolie Functions of Vitamin B12 504

Vitamin B12 Deficiency: Symptoms and Metabolie Bases 507

Vitamin Bi2 Requirements 510

Vitamin Bi2 Toxicity 511 Vitamin B6

Chemistry of Vitamin Be 511

Sources of Vitamin B6 511

Bioavailability and Absorption of Vitamin B6 511

Transport, Metabolism, and Tissue Accumulation of Vitamin B6 511

Metabolie Functions of Vitamin B6 513

Vitamin B6 Deficiency: Symptoms and Metabolie Bases 516

Vitamin B6 Requirements 517

Vitamin B6 Toxicity 517

Pantothenic Acid and Biotin 519

Lawrence Sweetman, Ph.D.

Pantothenic Acid

Microbial Synthesis and Structure of Pantothenic Acid 520

Absorption, Transport, and Excretion of Pantothenic Acid 520

Coenzyme A and ACYL Carrier Protein Synthesis and Degradation 522

Roles of Coenzyme A and ACYL Carrier Protein in Metabolism 524

Coenzyme A and Carnitine Interrelations 528 Dietary Sources, Recommended Intakes, and

Deficiency Symptoms 528 Biotin

Biotin Synthesis 529

Biotin Absorption, Transport, Excretion, and Degradation 530

Holocarboxylase Synthetase 531

Biotin-Containing Carboxylases 531

Holocarboxylase Synthetase Deficiency 536

Biotînidase Deficiency


Dietary Sources, Recommended Intakes,

and Deficiency Symptoms


Vitamin C


Mark Levine, M.D., Steven C. Rumsey, Ph.D., Yaohui Wang, M.D.,

Jae B. Park, Ph.D., and Rushad Daruwala, Ph.D.

Nomenclature, Structure, Formation, Chemical Characteristics,

and Degradation of Vitamin C


Food Sources, Absorption, and Bioavailability of Vitamin C


Transport of Ascorbate into Cells


Enzymatic Functions of Ascorbate


Nonenzymatic Reductive Functions of Ascorbate


Ascorbate Function and Tissue Distribution


Ascorbate Deficiency


Toxicity and Adverse Effects of Vitamin C


Recommended Ingestion


Vitamin K


John W. Suttie, Ph.D.

Vitamin K, An Antihemorrhagic Factor


Nomenclature of Vitamin K Active Compounds


Sources of Vitamin K


Absorption, Transport, and Metabolism of Vitamin K


Function of Vitamin K in the Synthesis of Specific Proteins


Physiological Roles of Vitamin K-Dependent Proteins


Vitamin K Deficiency


Assessment oF Vitamin K Status


Recommendations for Vitamin K Intake


Vitamin E


Ching K. Chow, Ph.D.

Nomenclature and Structure of Vitamin E


Absorption, Transport, and Metabolism of Vitamin E


Biological Functions of Vitamin E and

Free Radical-Induced Lipid Peroxidation


Functional Interactions of Vitamin E with other Nutrients


Deficiency, Toxicity, and Health Effects of Vitamin E 592

Biopotency and Sources of Various Forms of Vitamin E 594 Requirement for Vitamin E and Assessment of

Vitamin E Nutritional Status 596

26 Vitamin A 599

Chemistry and Physical Properties of Vitamin A and Carotenoids 600

Physiological Functions of Vitamin A 602 Absorption, Transport, Storage, and Metabolism of Vitamin A and Carotenoids 607

Retinoid-Binding Proteins and Transport of Retinoids 613

Nutritional Considerations of Vitamin A 618

27 Vitamin D 624

Photobiology of Vitamin D 625 Food Sources of Vitamin D and the Recommended

Dietary Allowances 629

Vitamin D in Bone Health 630

Vitamin D Metabolism and Function 632

Molecular Biology of Vitamin D 634

Biological Functions of 1,25(OH)2D in Noncalcemic Tissues 635 Recommendations for Satisfying the Vitamin D

Requirement for Maximum Bone Health 636

UNIT VI The Minerals

28 Calcium and Phosphorus 643

Chemical Properties of Calcium and Phosphorus 644

Physiological or Metabolic Functions of Calcium and Phosphorus 646

Hormonal Regulation of Calcium and Phosphate Metabolism 651

Calcium and Phosphate Homeostasis 654

Dietary Sources, Bioavailability, and Recommended

Intakes for Calcium and Phosphorus 660

Calcium and Phosphorus Deficiency and Assessment of Status 666 Clinical Disorders Involving Altered Calcium and Phosphorus Homeostasis 668

29 Magnesium 671

Chemistry of Magnesium 672

Food Sources and Dietary Intake of Magnesium 672

Absorption and Excretion of Magnesium 672

Body Magnesium Content 675

Physiological Roles of Magnesium 676

Magnesium Requirements 680

Magnesium Depletion 680

Diagnosis of Magnesium Deficiency 683

Magnesium Toxicity 683

30 Sodium, Chloride, and Potassium 686

Hwai-Ping Sheng, Ph.D.

Functions of Sodium, Chloride, and Potassium 687

Sodium, Chloride, and Potassium Balance 694

Regulation of Sodium, Chloride, and Potassium Balance 697

Sodium and Chloride Imbalance and Its Consequences 704

Potassium Imbalance and Its Consequences 705

Nutritional Considerations 707

Roy D. Baynes, M.D., Ph.D., and Martha H. Stipanuk, Ph.D.

Biological Functions of Iron 712

Proteins of Iron Transport and Iron Storage 715 Regulation of Concentrations of Proteins of Iron Transport and Storage 720

Body Iron Compartments 722

Internal Iron Exchange and Iron Delivery to Cells 722

External Iron Exchange and Iron Absorption 725

Recommended Dietary Intakes of Iron 731

Assessment of Iron Status


Iron Deficiency


Iron Excess


Zinc, Copper, and Manganese


James C. Fleet, Ph.D.

The Role of Zinc, Copper, and Manganese in Enzyme Systems


Requirements and Food Sources of Zinc, Copper,

and Manganese


Absorption, Transport, Storage, and Excretion of Zinc,

Copper, and Manganese


Selected Functions of Zinc, Copper, and Manganese


Assessment of Zinc, Copper, and Manganese Status

and Deficiency Symptoms


Toxicity of Zinc, Copper, and Manganese




Hedley C. Freake, Ph.D.

Uniqueness of Iodine


Production and Metabolism of Thyroid Hormones


Mechanism of Action of Thyroid Hormones


Physiological Functions of Thyroid Hormones


Iodine Deficiency


Iodine Requirements




Roger A. Sunde, Ph.D.

Chemistry of Selenium


Selenium Deficiency and Essentiality


Selenium Absorption, Distribution, and Excretion


Metabolic Pathways of Selenium


Selenium Incorporation into Selenoproteins


Mammalian Selenoproteins


Selenium Requirements


Mechanism and Function of Regulation of GPX1

Expression by Selenium


Selenium and Vitamin E 805

Selenium Toxicity 806

Selenium and Cancer 806

35 Fluoride 810

Overview of Fluoride 811

Dental Fluorosis and Dental Caries 811

Fluoride Intake 813

Fluoride Physiology 817

Acute Fluoride Toxicity 821

Chronic Fluoride Toxicity 822

36 The Ultratrace Elements 825

Forrest H. Nielsen, Ph.D.

Characteristics of Ultratrace Elements 826

Boron 826

Chromium 828

Molybdenum 831

Prospective Ultratrace Elements—Nickel, Vanadium, Silicon,

Arsenic, and Fluorine 833

Abstruse Ultratrace Elements 840


Nutrition, Diet, and Health

37 Body Fluids and Water Balance 843

Hwai-Ping Sheng, Ph.D.

Body Water Compartments 844

Water Balance 850

Renal Excretion of Water 853

Regulation of Water Balance 858

Abnormal States of Osmolarities and Volumes 862

38 Diet and Oral Disease 866

Dominick P. DePaola, D.D.S., Ph.D., and Charles F. Schachtele, Ph.D.

Perspectives on the Role of Carbohydrates in Oral Disease 867

Biological Basis for the Role of Carbohydrates in Oral Disease 869

Human Data Linking Carbohydrates to Oral Disease 873

The Role of Carbohydrates and Foods in Oral Disease Prevention 875

The Role of Carbohydrates in Other Oral Diseases 879

Prevention of Oral Disease 880

39 Fuel Utilization by Skeletal Muscle During Rest and

During Exercise 882

Anton J. M. Wagenmakers, Ph.D.

Skeletal Muscle Fuel Utilization During Rest 883

The Energy Cost of Movement 886

Fuels for Sprinting 887

Fuels for the Marathon 890

Skeletal Muscle Adaptations in Response to Training and the

Consequences for Fuel Utilization and Performance 893

Fuels for Other Sporting Events 894

How Nutrition May Help Improve Performance 895

Protein and Amino Acid Metabolism in Skeletal

Muscle During Rest and During Exercise 898

Skeletal Muscle Adaptations in Response to Disuse and Disease and the Consequences for Fuel Utilization and Weil-Being During Normal Daily Life 898

40 Detoxification and Protective Functions of Nutrients 901

Defense Systems 902

Oxidative Processes 902

Detoxification of Xenobiotic Compounds 908

41 Nutrition, Lipids, and Cardiovascular Disease 917

Henry N. Ginsberg, M.D., and Wahida Karmally, M.S., R.D.

Atherosclerotic Cardiovascular Disease 918

Effects of Diet on Plasma Lipids and Lipoproteins 927

Diet, Blood Lipids, and Atherosclerosis 936

Dietary Treatment of Hypercholesterolemia 938

42 Translating Biochemical and Physiological Requirements into Practice 945

Food as a Source of Nutrients 946 Recommended Dietary Allowances and Dietary

Reference Intakes 946

Dietary Advice—Goals and Guidelines 951

Food Guides 952

Food Labels 955

Index 961


Nutrition is an ever-changing field. Standard safety precautions must be followed, but as new research and clinical experience broaden our knowledge, changes in treatment and drug therapy become necessary or appropriate. Readers are advised to check the product information currently provided by the manufacturer of each drug to be administered to verify the recommended dose, the method and duration of administration, and the contraindications. It is the responsibility of the treating physician, relying on experience and knowledge of the patient, to determine dosages and the best treatment for the patient. Neither the publisher nor the editor assumes any responsibility for any injury and/or damage to persons or property.

The Publisher


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