Food Conversion

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Food energy – methods of analysis and conversion factors

FAO FOOD AND NUTRITION PAPER

77

Ingested energy (IE) = gross energy (GE) Faecal energy (FE) Combustible gas (GaE) (from microbial fermentation) Digestible energy (DE) Urinary energy (UE) Surface energy (SE) Metabolizable energy (ME) Heat of microbial fermentation Obligatory thermogenesis, i.e. excess heat relative to glucose during ATP synthesis Net (metabolizable) energy (NME) Non-obligatory dietary thermogenesis Thermogenesis due to effects of cold, drugs, hormones, bioactive compounds or other stimulants Net energy for maintenance (NE) Basal metabolism Physical activity

Food energy – methods of analysis and conversion factors

FAO FOOD AND NUTRITION PAPER

77

Report of a technical workshop Rome, 3–6 December 2002

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS Rome, 2003

CONTENTS Foreword CHAPTER 1: INTRODUCTION 1.1 Historical background 1.2 Background to the technical workshop 1.3 Rationale for the technical workshop CHAPTER 2: METHODS OF FOOD ANALYSIS 2.1 Analytical methods for proteins in foods 2.2 Analytical methods for fats in food 2.3 Analytical methods for carbohydrates in foods v 1 1 2 4 7 7 11 12

CHAPTER 3: CALCULATION OF THE ENERGY CONTENT OF FOODS – ENERGY CONVERSION FACTORS 18 3.1 Joules and calories 18 3.2 Theoretical framework for an understanding of food energy conversion factors 19 3.3 Flow of energy through the body – a brief overview 20 3.4 Conceptual differences between metabolizable energy and net metabolizable energy 22 3.5 Current status of food energy conversion factors 23 3.6 Standardization of food energy conversion factors 32 3.7 The relationship between food energy conversion factors and recommendations for energy requirements 33 3.8 Other practical implications related to the use of food energy conversion factors 37 CHAPTER 4: SUMMARY – INTEGRATION OF ANALYTICAL METHODS AND FOOD ENERGY CONVERSION FACTORS 57 4.1 Protein 57 4.2 Fat 58 4.3 Carbohydrate 58 4.4 Alcohol, polyols, organic acics and other food energy producing substrates 60

iv REFERENCES 61

ANNEXES 67 I: Participants – Technical Workshop on Food Energy: Methods of Analysis and Conversion Factors 68 II: Members of Working Group 5, their recommendations and the modifications to those recommendations made by the current technical workshop participants 72 III: Corrections to the diet and/or standard energy requirements when using metabolizable energy (ME) or net metabolizable energy (NME) factors 78 IV: Comparisons of energy contents of breastmilk, infant formula and selected foods for infants and young children using ME and NME energy conversion factors 82

v

FOREWORD
Ever since its inception, one of FAO’s primary objectives has been to assure an adequate, nutritionally sound and safe food supply. This has required periodic assessments of the food supply and its comparison with the needs of the population. To enable this, knowledge of human food requirements, both qualitative and quantitative, is required. Thus, one of the earliest and ongoing activities of FAO’s Food and Nutrition Division has been to determine the energy and nutrient requirements of humans. FAO’s first review of energy (“calorie”) requirements was made in 1949. This was followed by four subsequent reviews, the most recent being in 2001. However, recommendations for optimal energy requirement become practical only when they are related to foods, which provide the energy to meet those requirements. This linking of energy requirements with energy intake depends on knowledge of the amounts of energy-providing components in foods and the use of a valid expression of the energy values of those components. At first glance, this may seem simple but, with the increasing number of available methods of analysis and the enhanced sophistication of the analytical methods used to determine food components, there are myriad possible options for expressing the...
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