Clinical Nutrition

Marinos Elia, Olle Ljungqvist, Rebecca J. Stratton, Susan A. Lanham-New

• Publisher: Wiley-Blackwell
• Year: 2013
• Print ISBN: 9781405168106
• eBook ISBN: 9781118457740
• Edition: 2
• Topic: Medicine
• Subtopic: Nutrition, Dietics & Bariatrics

This second edition of Clinical Nutrition, in the acclaimed textbook series by the Nutrition Society, has been revised and updated in order to:

• Provide students with the required scientific basis in nutrition, in the context of a systems and health approach.
• Enable teachers and students to explore the core principles of nutrition and to apply these throughout their training to foster critical thinking at all times. Each chapter identifies the key areas of knowledge that must be understood and also the key points of critical thought that must accompany the acquisition of this knowledge.
• Are fully peer reviewed to ensure completeness and clarity of content, as well as to ensure that each book takes a global perspective and is applicable for use by nutritionists and on nutrition courses throughout the world.

Ground breaking in scope and approach, with an additional chapter on nutritional screening and a student companion website, this second edition is designed for use on nutrition courses throughout the world and is intended for those with an interest in nutrition in a clinical setting. Covering the scientific basis underlying nutritional support, medical ethics and nutritional counselling, it focuses solely on the sick and metabolically compromised patient, dealing with clinical nutrition on a system by system basis making the information more accessible to the students.

This is an essential purchase for students of nutrition and dietetics, and also for those students who major in other subjects that have a nutrition component, such as food science, medicine, pharmacy and nursing. Professionals in nutrition, dietetics, food sciences, medicine, health sciences and many related areas will also find this an important resource.

Libraries in universities, medical schools and establishments teaching and researching in the area of nutrition will find Clinical Nutrition a valuable addition to their shelves.

1

Principles of Clinical Nutrition: Contrasting the Practice of Nutrition in Health and Disease

Marinos Elia

Institute of Human Nutrition,University of Southampton,Southampton, UK

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Key messages

• To understand how to best meet the nutritional needs of an individual, the distinction between physiology in health and pathophysiology in disease needs to be carefully considered.
• For some groups of patients, the requirements are higher than those in health, while for other groups of patients they are lower. If recommendations for healthy individuals are applied to patients with certain types of disease, they may produce harm.
• In health, only the oral route is used to provide nutrients to the body. In clinical practice, other routes can be used. The use of the intravenous route for feeding raises a number of new issues.
• Alterations in nutritional therapy during the course of an acute disease may occur because the underlying disease has produced new complications or because it has resolved. Similarly, in more chronic conditions there is a need to review the diet at regular intervals.

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1.1 Introduction

Clinical nutrition focuses on the nutritional management of individual patients or groups of patients with established disease, in contrast to public health nutrition, which focuses on health promotion and disease prevention in the general population. The two disciplines overlap, however, especially in older people, who are often affected by a range of disabilities or diseases. Working together, instead of independently, the two disciplines are more likely to facilitate successful implementation of local, national, and international policies on nutrition. To understand the overlap between them, it is necessary to consider not only some of the principles of nutrition that apply to health, but also special issues that apply to the field of clinical nutrition. These include altered nutritional requirements associated with disease, disease severity and malnutrition, and nonphysiological routes of feeding using unusual feeds and feeding schedules. This introductory chapter provides a short overview of these issues, partly because they delineate qualitative or quantitative differences between health and disease, and partly because they form a thread that links subsequent sections of this book, which is divided into discrete chapters addressing specific conditions.

It is now possible to feed all types of patients over extended periods of time, including those who are unconscious, unable to eat or swallow, or have little or no functional gastrointestinal tract. It is possible to target specific patient groups with special formulations, and even to change the formulation in the same patient as nutritional demands alter during the course of an illness. Since some of these formulations may be beneficial to some patient groups and detrimental to other groups or to healthy subjects, the distinction between physiology in health and pathophysiology in disease needs to be considered carefully. It is hoped that some of the principles outlined here will help to establish a conceptual framework for considering some of the apparently diverse conditions discussed in this textbook.

1.2 The spectrum of nutritional problems

Clinical nutrition aims to treat and prevent suffering from malnutrition. However, there is no universally accepted definition for ‘malnutrition’ (literally, ‘bad nutrition’). The following definition, which encompasses both under- and over-nutrition, is offered for the purposes of this chapter.

Malnutrition is a state of nutrition in which a deficiency or excess (or imbalance) of energy, protein, and other nutrients causes measurable adverse effects on tissue/body function (shape, size, and composition) and clinical outcome.

In this chapter and elsewhere, however, the term ‘malnutrition’ is mainly used to refer to under- rather than over-nutrition.

Both under- and over-nutrition have adverse physiological and clinical effects. Those relating to under-nutrition (Table 1.1) are diverse, which explains why malnourished patients may present to a wide range of medical disciplines. Several manifestations may occur simultaneously in the same individual, although some predominate. They may be caused by multiple deficiencies. Specific nutrient deficiencies may also have diverse effects, affecting multiple systems, but it is not entirely clear why the same deficiency can present in a certain way in one subject and a different way in another. For example, it is not clear why some patients with deficiency of vitamin B₁₂ present to the haematologist with megaloblastic anaemia, others to the neurologist with neuropathy and other neurological manifestations (e.g. subacute combined degeneration of the cord), and still others to the geriatrician with cognitive impairment or dementia.

Table 1.1 Physical and psychosocial effects of under-nutrition.

Adverse effect	Consequence
Physical
Impaired immune responses	Predisposes to infection
Reduced muscle strength and fatigue	Inactivity, inability to work effectively, and poor self-care. Abnormal muscle (or neuromuscular) function may also predispose to falls or other accidents
Reduced respiratory muscle strength	Poor cough pressure, predisposing to and delaying recovery from chest infection
Inactivity, especially in bed-bound patient	Predisposes to pressure, sores, and thromboembolism
Impaired thermoregulation	Hypothermia, especially in the elderly
Impaired wound-healing	Failure of fistulae to close, un-united fractures, increased risk of wound infection resulting in prolonged recovery from illness, increased length of hospital stay, and delayed return to work
Foetal and infant programming	Predisposes to common chronic diseases, such as cardiovascular disease, stroke, and diabetes in adult life
Growth failure	Stunting, delayed sexual development, and reduced muscle mass and strength
Psychosocial
Impaired psychosocial function	Even when uncomplicated by disease, undernutrition causes apathy, depression, self-neglect, hypochondriasis, loss of libido, and deterioration in social interactions. It also affects personality and impairs mother–child bonding

The spectrum of presentations is more diverse than this would indicate because protein–energy malnutrition frequently coexists with various nutrient deficiencies. For example, patients with gastrointestinal problems are frequently underweight and at the same time exhibit magnesium, sodium, potassium, and zinc deficiencies, due to excessive losses of these nutrients in diarrhoea or other gastrointestinal effluents. There may also be problems with absorption; for example, patients with Crohn’s disease affecting the terminal ileum, where vitamin B₁₂ is absorbed, are at increased risk of developing B₁₂ deficiency. Patients who have had surgical removal of their terminal ileum or stomach, which produces the intrinsic factor necessary for B₁₂ absorption, fail to absorb vitamin B₁₂. Isolated nutrient deficiencies may also occur, for example iron deficiency due to heavy periods in otherwise healthy women.

Another complexity is the interaction between nutrients, which may occur at the level of absorption, metabolism within the body, or excretion. One nutrient may facilitate the absorption of another; for example, glucose enhances the absorption of sodium (on the glucose–sodium co-transporter). This is the main reason why oral rehydration solutions used to correct salt deficiency due to diarrhoea (or fluid losses due to other gastrointestinal diseases) contain both salt and glucose. In contrast, other nutrients compete with each other for absorption. For example, because of competition between zinc and copper for intestinal absorption, administration of copper may precipitate zinc deficiency, especially in those with borderline zinc status. Other nutrients interact with each other during tissue deposition. Accretion of lean tissue requires multiple nutrients, and lack of one of them, such as potassium or phosphate, can limit its deposition, even when adequate amounts of protein and energy are available (Figure 1.1). This emphasises the need to provide all necessary nutrients in appropriate amounts and proportions.

Figure 1.1 Effect of omitting potassium (K) and phosphate (P) from a parenteral nutrition regimen on the nitrogen (N) balance of depleted patients receiving hypercaloric feeding. Data from Rudman et al. (1975).

1.3 Nutritional requirements

Effect of disease and nutritional status

Fluid and electrolytes

The principles of nutrient requirements in healthy individuals are described in Introduction to Human Nutrition (Gibney et al., 2009), an earlier volume in this textbook series. The average nutrient intake refers to the average intake necessary to maintain nutrient balance. The reference nutrient intake (RNI) refers to the intake necessary to satisfy the requirements of 97.5% of the healthy population (+2 standard deviations from the average nutrient intake). In patients with a variety of diseases, the requirements are more variable (Figure 1.2): for some groups of patients, they are higher than for those in health, while for other groups they are lower. For example, in patients with gastrointestinal fluid losses, the requirement for sodium may be double the RNI, while in patients with severe renal or liver disease who retain salt and water, the requirements may be well below the average nutrient requirement for healthy subjects ingesting an oral diet. The requirements for potassium and phosphate may also be well below the RNI for patients with severe renal disease in whom there is failure of excretion. Therefore, if recommendations for healthy individuals are applied to patients with certain types of disease, they may produce harm. A general guide to the requirements for sodium and potassium in patients with gastrointestinal fluid loss (above those for maintenance) is provided in Table 1.2, which shows the electrolyte content of various fluids. A person with a loss of 1.5 litres of small-intestinal fluid may require ~150 mmol of sodium above maintenance (the RNI for sodium is 70 mmol/day according to UK reference standards), whereas loss of the same volume of nasogastrically aspirated fluid requires only ~90 mmol extra sodium. Note that the requirements for potassium in patients losing gastrointestinal fluids are generally much lower than those for sodium (Table 1.2).

Figure 1.2 Frequency distribution of nutrient requirements in health and disease.

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Table of contents

• Cover
• The Nutrition Society Textbook Series
• Title page
• Copyright page
• Contributors
• Series Foreword
• Preface
• First Edition Acknowledgements
• 1 Principles of Clinical Nutrition: Contrasting the Practice of Nutrition in Health and Disease
• 2 Nutritional Screening and Assessment
• 3 Water and Electrolytes
• 4 Over-nutrition
• 5 Under-nutrition
• 6 Metabolic Disorders
• 7 Eating Disorders
• 8 Adverse Reactions to Foods
• 9 Nutritional Support
• 10 Ethics and Nutrition
• 11 The Gastrointestinal Tract
• 12 Nutrition in Liver Disease
• 13 Nutrition and the Pancreas
• 14 The Kidney
• 15 Nutritional and Metabolic Support in Haematological Malignancies and Haematopoietic Stem-cell Transplantation
• 16 The Lung
• 17 Nutrition and Immune and Inflammatory Systems
• 18 The Heart and Blood Vessels
• 19 Nutritional Aspects of Disease Affecting the Skeleton
• 20 Nutrition in Surgery and Trauma
• 21 Infectious Diseases
• 22 Nutritional Support in Patients with Cancer
• 23 Paediatric Nutrition
• 24 Cystic Fibrosis
• 25 Illustrative Cases
• Index
• Access to Companion Site