Advanced Nutrition and Dietetics in Obesity

Catherine Hankey, Kevin Whelan, Catherine Hankey

• Publisher: Wiley-Blackwell
• Year: 2017
• ISBN:
  9781118857960
• Edition: 1
• Topic: Medicina
• Subtopic: Nutrición, dietética y bariatría

This addition to the British Dietetic Association Advanced Nutrition and Dietetics book series is written for clinicians and researchers who work with any aspect of obesity and its comorbid conditions. Featuring contributions from leading researchers and practitioners from around the globe Advanced Nutrition and Dietetics in Obesity offers a uniquely international perspective on what has become a worldwide public health crisis.

Chapters cover a full range of new ideas and research on the underlying drivers of obesity in populations including discussions on the genetic and clinical aspects of obesity, along with expert recommendations on how to effectively manage and prevent this chronic and persistent disease.

Providing a comprehensive overview of the key literature in this field, Advanced Nutrition and Dietetics in Obesity is an invaluable resource for all those whose work should or does embrace any aspect of obesity.

SECTION 1
Introduction

Chapter 1.1
Definition, prevalence and historical perspectives of obesity in adults

Peter Kopelman

St George’s, University of London, London, UK

1.1.1 Definitions of overweight and obesity

In clinical practice, body fat is most commonly and simply estimated by using a formula that combines weight and height. The underlying assumption is that most variations in weight for persons of the same height is due to fat mass. The formula most frequently used in epidemiological studies is the body mass index (BMI), which is weight in kilograms divided by the square of the height in metres. BMI is strongly correlated with densitometry measurements of fat mass adjusted for height in middle‐aged adults. The main limitation of BMI is that it does not distinguish fat mass from lean mass. Table 1.1.1 identifies the cut‐off points applied by the World Health Organisation for BMI classification in adults [1].

Table 1.1.1 Cut‐off points applied by the World Health Organisation for the classification of overweight and obesity

BMI*	WHO classification	Popular description
<18.5	Underweight	‘Thin’
18.5–24.9	Healthy weight	‘Healthy’
25.0–29.9	Overweight	‘Overweight’
30.0–34.9	Obesity I	‘Obese’
35.0–39.9	Obesity II	‘Obese’
40 or greater	Obesity III	‘Morbidly or seriously obese’

* BMI is the weight in kilograms divided by the square of the height in metres.

Data sourced from http://apps.who.int/bmi/index.jsp?introPage=intro_3.html

Although BMI is used to classify individuals as ‘obese’ or ‘overweight’, it is only a proxy measure of the underlying problem of excess fat. As a person’s body fat increases, both their BMI and their future risk of obesity‐related illness also rise, although there is still some uncertainty about the exact nature of the relationship, especially in children.

Measurement of body circumference is an additional indicator of health risk in an overweight or obese person: excess visceral (intra‐abdominal) fat is a risk factor for long‐term conditions independent of total adiposity. Waist circumference and the ratio of waist circumference to hip circumference are practical measures for assessing upper‐body fat distribution.

Skinfold thickness, measured with calipers, provides a more precise assessment of body fat, especially if taken at multiple sites. Skinfolds are useful in the estimation of fatness in children, for whom standards have been published. However, the measurements are more difficult to make in adults (particularly in the very obese), are subject to considerable variation between observers, require accurate calipers and do not provide any information on abdominal and intramuscular fat. In general, they are not superior to simpler measures of height and weight. Table 1.1.2 lists the practical measures for the assessment of an obese person.

Table 1.1.2 Clinical methods for the assessment of an individual with obesity

Characteristic of obesity measured	Methods
Body composition	BMI Underwater weighing Dual‐energy X‐ray absorptiometry (DEXA) Isotope dilution Bioelectrical impedance Skinfold thickness
Regional distribution of fat	Waist circumference; waist‐to‐hip ratio Computerised axial tomography Ultrasound Magnetic resonance imaging (MRI)
Energy intake	Dietary recall or record ‘macronutrient composition’ by prospective dietary record or dietary questionnaire
Energy expenditure	Doubly labelled water Indirect calorimetry (resting) Physical activity level (PAL) by questionnaire Motion detector Heart rate monitor

Why use BMI?

BMI is an attractive measure because it is an easy, cheap and non‐invasive means of assessing excess body fat. Prior to the application of BMI, clinicians referred to ‘ideal’ weight tables, which were derived from the weight–height tables provided by the Metropolitan Life Insurance Company (1959), based on subsequent mortality of insured adults in the USA and Canada [2]. However, prospective epidemiological data confirmed the impreciseness of the term ‘ideal’ even within a North American population (despite attempts to sharpen this with measures of body frame size), and its inapplicability when applied in a global context. BMI has been used widely around the world, permitting comparisons between areas, across population sub‐groups and over a long period. Another advantage of BMI is the availability of published thresholds and growth references to which children’s BMI can be compared. BMI in children varies with age and gender, which prevents the use of fixed thresholds as in adults [3,4]. Equivalent growth references do not exist for other measures such as waist circumference.

Interpretation of BMI: defining a ‘healthy weight’ for a particular society

There are methodological problems that derive from a definition based on total mortality rates. People frequently lose weight as a consequence of illness that is ultimately fatal, which was unrecognised at the time of the survey. This gives the appearance of higher mortality among those with lower weights: reverse causation. The effect can be minimised by either excluding persons with diagnoses that might affect weight and/or those who report recent weight loss, or excluding those who die during the first years of follow‐up. A second major concern is confounding factors that may distort the association between body weight and mortality – cigarette smoking is of particular importance. Overweight and obesity cause or exacerbate a large number of health problems, both independently and in association with other diseases, and are among the most significant contributors to ill health [5]. Unfortunately, many of the health risks associated with increasing body weight begin their manifestation in children and young people – of great current concern is the increasing prevalence of type 2 diabetes and associated medical complications in young overweight adults. There is a close relationship between BMI and the incidence of many long‐term conditions caused by excess fat: type 2 diabetes, hypertension, coronary heart disease and stroke, metabolic syndrome, osteoarthritis (OA) and cancer. An overview of the association between BMI and the development of a range of diseases is given in Table 1.1.3.

Table 1.1.3 Risks and diseases associated with increasing body weight

Metabolic syndrome	30% of middle‐aged people in developed countries have features of metabolic syndrome
Type 2 diabetes	90% of people with type 2 diabetes have BMI >23 kg/m^2
Hypertension	5x risk in obesity 66% hypertension linked to excess weight 85% hypertension associated with BMI >25 kg/m^2
Coronary artery disease (CAD) and stroke	3.6x increase in risk of CAD for each unit change in BMI Dyslipidaemia progressively develops as BMI increases from 21 kg/m^2 with rise in small‐par...