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National Collaborating Centre for Acute Care (UK). Nutrition Support for Adults: Oral Nutrition Support, Enteral Tube Feeding and Parenteral Nutrition. London: National Collaborating Centre for Acute Care (UK); 2006 Feb. (NICE Clinical Guidelines, No. 32.)

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Nutrition Support for Adults: Oral Nutrition Support, Enteral Tube Feeding and Parenteral Nutrition.

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2Malnutrition and the principles of nutrition support

2.1. Introduction

The purpose of this guideline is to present evidence and guidance related to nutrition support. In view of the problems related to studies of nutritional intervention (described in section 1.12), the Guideline Development Group (GDG) agreed to base some of the recommendations on principles derived from understanding the causes and effects of malnutrition in patients. This chapter covers these issues.

2.2. The causes of malnutrition

The main causes of malnutrition can be categorised under four headings (summarised in Table 7):

Table 7. Factors contributing to disease related malnutrition.

Table 7

Factors contributing to disease related malnutrition.

  • impaired intake;
  • impaired digestion and or absorption;
  • altered metabolic nutrient requirements; and
  • excess nutrient losses.

The relative importance of each class of problem varies and multiple factors often occur simultaneously. Physical factors, usually associated with illness, are the predominant cause of malnutrition in UK adults, although psychosocial issues have significant effects on dietary intake in some groups (e.g. the socially isolated, the bereaved, poor quality diets in low income groups and some older subjects). Since malnutrition both predisposes to disease (Table 7) and is simultaneously an outcome of disease, patients may enter a downward spiral of ill-health due to malnutrition-disease interactions.

2.3. The effects of malnutrition

Malnutrition detrimentally effects physical function, psychosocial well-being and the outcome of disease. It can affect every system and tissue of the body 185,335, see Table 8.

Table 8. Some physical and psycho-social effects of malnutrition.

Table 8

Some physical and psycho-social effects of malnutrition.

2.4. The prevalence of malnutrition

There are many different anthropometric, clinical and biochemical criteria that have been used to assess malnutrition and these have resulted in widely varying reports of its prevalence. One of the simplest criteria is current weight status (e.g. body mass index; BMI). The proportion of underweight adults (BMI<20 kg/m2) in the UK varies considerably according to care setting: 10–40% in hospitals and care homes; ≤ 5% in the general population at home, and >10% in those at home with chronic diseases of the lung and gastrointestinal tract, or those who have had surgery in the previous 6 weeks. The ‘Malnutrition Universal Screening Tool’ (‘MUST’)94, which incorporates both current weight status and unintentional weight loss, has identified more than 10% of the general population aged 65 years and over as being at medium or high risk of malnutrition92–94,336. In hospitalised patients, the same degree of risk is seen in 10–60% depending on medical condition and patients’ age. Similar very high prevalence’s of nutritional risk are seen in residents of care homes but although most malnutrition is found in the community (>95%), most malnutrition related expenditure occurs in hospital9,87. However, both care settings make a substantial contribution to total costs.

The prevalence of individual nutrient deficiencies is also disturbing, especially in older subjects. For example, in people aged 65 years and over109, folate deficiency affects 29% of those who are “free living” (8% in severe form) and 35% of those in institutions (16% in severe form). Similarly, vitamin C deficiency in such people affects 14% of those who are free living (5% in a severe form) and 40% of those in institutions (16% in severe form). Nutrient deficiencies and protein-energy malnutrition commonly coexist335.

2.5. Principles underlying intervention

The difficulties inherent in nutrition support mean that there is little hard evidence to assist with decisions on how and when to treat patients who are either malnourished or at risk of becoming so. However, sensible approaches can be derived from understanding 3 types of observations:

  1. Cross-sectional studies suggest that nutritionally related problems are likely to occur in individuals who are thin or who have recently lost weight94,335,336 e.g. those with BMIs of <20 kg/m2 and especially <18.5 kg/m2 and/or those who have recently lost >5% of their usual body weight, especially those who have lost >10%.
  2. Studies in healthy volunteers show that measures such as muscle function203,335 decline within a few days of complete starvation, and after more than 5–7 days of little or no intake there is significant detriment in several bodily functions including many of those listed in Table 8. These ill effects reverse promptly with the provision of adequate feeding.
  3. Studies in malnourished patients show rapid functional benefits when adequate feeding is provided. These changes can occur well before the weight lost has been regained (e.g. malnourished patients have low collagen deposition rates in surgical wounds but show improved deposition within days of receiving nutrition support374).

With these observations in mind, good nutrition should benefit both those who are already overtly malnourished in terms of BMI or recent unintentional weight loss and those who are developing nutritional risks by having eaten little or nothing or be likely to eat little or nothing for over 5 days. In addition, nutrition support can often provide simple direct benefits by:

  • Keeping patients who are eating inadequately, alive for long enough for specific medical or surgical interventions to take effect.
  • Making malnourished patients feel better, improving their ability to cope with ill-health.
  • Maintaining strength through patients’ illnesses so that their recuperation is shortened and they are less susceptible to further problems.
  • Providing long-term support for those patients with chronic inability to eat, drink or absorb adequately.

The principles above underlie many of the recommendations proposed in these Guidelines. They are also in keeping with physical, psychological and social improvements that occur during repletion185.

Copyright © 2006, National Collaborating Centre for Acute Care.

Apart from any fair dealing for the purposes of research or private study, criticism or review, as permitted under the Copyright, Designs and Patents Act, 1988, no part of this publication may be reproduced, stored or transmitted in any form or by any means, without the prior written permission of the publisher or, in the case of reprographic reproduction, in accordance with the terms of licences issued by the Copyright Licensing Agency in the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publisher at the UK address printed on this page.

The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant laws and regulations and therefore for general use.

The rights of National Collaborating Centre for Acute Care to be identified as Author of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act, 1988.

Bookshelf ID: NBK49258

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