Key issues in the prevention of obesity Timothy P Gill Post Graduate Nutrition and Dietetic Centre, Rowett Research Institute, Aberdeen, UK

Obesity is a serious, chronic medical condition which is associated with a wide range of debilitating and life-threatening conditions. It imposes huge financial burdens on health care systems and the community at large. Obesity develops over time and once it has done so, is difficult to treat.Therefore, the prevention of weight gain offers the only truly effective means of controlling obesity. Very little research has directly addressed the issue of obesity prevention and previous efforts to prevent obesity amongst individuals, groups or whole communities have had very limited success. However, we have learned sufficient from past preventive activities to realise that the management of obesity will require a comprehensive range of strategies with actions that target those with existing weight problems, those at high risk of developing obesity as well as the community as a whole. The prevention and management of obesity in children should be considered a priority as there is a high risk of persistence into adulthood.

Obesity is a serious medical condition which is associated with a wide range of debilitating, chronic and life-threatening conditions. It imposes huge financial burdens on health care systems and the community at large. The fact that obesity prevalence continues to increase at an alarming rate in almost all regions of the world is, therefore, of major concern. However, despite the potential gains to be achieved from reducing the incidence and prevalence of obesity in a population, surprisingly little attention has so far been given to developing strategies aimed at the prevention of obesity. This chapter examines the key role that prevention should play in the management of obesity and identifies potential prevention strategies and priority areas for action.

The rationale behind obesity prevention Dr Timothy p GUI, The rationale behind obesity prevention is several fold. First, obesity Post Graduate Nutrition develops over time and, once it has done so, is very difficult to treat. A and Dietetic Centre, number of analyses have identified the failure of obesity treatments (with Rowett Research

Institute,

,

•,,

•

c

•

.

•

i

u

\

Greenbum Road t " e P o s s i ble exception of gastric surgery in the seriously obese) to Buctibum, achieve long-term success1"3. Second, the health consequences associated Aberdeen AB2! 9SB, UK w i t h obesity result from the cumulative metabolic and physical stress of British Medical Bulletin 1997;53 (No. 2):359-388

©The Britith Council 1997

Obesity

excess weight over a long period of time and may not be fully reversible by weight loss4-5. Third, the proportion of the population that is either overweight or obese in many developed countries is now so large that there are no longer sufficient health care resources to offer treatment to all6. It can be argued, therefore, that the prevention of weight gain (or the reversal of small gains) would be easier, less expensive, and potentially more effective than to treat obesity after it has fully developed.

Is obesity preventable? The fact that obesity prevalence is rising rapidly and unchecked in almost all areas of the world has led some people to question whether it is possible to prevent excessive gains in body weight over time. However, as mentioned previously, there has so far been little research addressing this question comprehensively. There has only been one controlled intervention study published to date that has been specifically aimed at preventing weight gain in adults. Forster et al? found that after 1 year of a low impact programme (involving four nutrition education sessions, a monthly weight control information newsletter, and an incentive program), those in the treated group had lost about 1 kg in weight, while the weights of those in the control group remained unchanged. Further subgroup analysis showed that the greatest impact was among men, individuals over the age of 50, non-smokers, and those with little prior experience with formal weight loss services. The results of this short-term study are not sufficient to inspire confidence in our ability to prevent obesity. Indirect evidence from a variety of sources, however, indicates that obesity prevention strategies could indeed prove to be effective in combating the escalating problem of obesity. Given a suitable environment, many people are able to control their weight successfully over long periods of time. This is true both from an individual and from a population perspective. In certain parts of the world such as Japan, for example, the fact that obesity rates are currently low suggests that humans are not biologically destined to become obese. Furthermore, the explosion in rates of obesity has mirrored similar epidemics in noncommunicable diseases such as coronary heart disease which are now abating in countries where preventive strategies to deal with these have been adopted. Comprehensive obesity prevention programmes have been introduced very recently in a small number of countries (e.g. Singapore), but not enough time has yet elapsed to be able to evaluate their success. However, the level of obesity in Finnish men from higher education grades has shown a decline since 198572. 360

British Mmdical Bulletin 1997;53 (No. 2)

Prevention of obesity

Perhaps the strongest evidence for the preventability of obesity comes from the successful management of childhood obesity. A number of researchers8^11 have shown that effective management and support of overweight and obese children can significantly reduce the number of children who carry their weight problem into adulthood. The long term prevention of weight gain in these studies was achieved during the difficult transition periods of childhood and adolescence when weight gain can be a major problem. It is also interesting that in studies where children were treated together with their parents, the children were successful in reducing and maintaining their weight loss whilst over time the adults returned to their pre-study body weight8.

Obesity prevention strategies The aims of obesity prevention

The effective control of obesity requires the development of coherent strategies that tackle the main issues relating to the prevention of: (i) the development of overweight in normal weight individuals; (ii) the progression of overweight to obesity in those who are already overweight; (iii) weight regain in those who have been overweight or obese in the past but who have since lost weight; and (iv) further worsening of a condition already established. This involves action at several levels.

Levels of preventive action

The traditional classification of prevention interventions into primary, secondary and tertiary was originally developed to describe actions in relation to acute conditions with an identifiable, unifactoral cause. The objective of primary prevention was seen as decreasing the number of new cases (incidence): secondary prevention was to lower the rate of established cases in the community (prevalence); and tertiary prevention was to stabilise or reduce the amount of disability associated with the disorder. Thus, attention is focused on individual risk factors when applying this system to a multi-factorial condition such as coronary heart disease (CHD). Primary prevention of CHD might involve national programmes to control blood cholesterol levels; secondary prevention may deal with reducing CHD risk in those with existing elevated blood cholesterol levels; and tertiary action would be associated with preventing re-infarction in those who had a previous heart attack. Use of the traditional classification system for obesity prevention strategies, however, results in a great deal of ambiguity and confusion. For British M « W Bulletin 1997;53 (No. 2)

361

Obesity

example, does primary obesity prevention refer to the prevention of overweight people from becoming obese, or is this secondary prevention. Is tertiary prevention concerned with the prevention of obesity progressing into more severe obesity or rather with the control of comorbid conditions such as hypertension. To avoid confusion when discussing strategies for the prevention of chronic, multi-factorial conditions such as obesity, the US Institute of Medicine12 has proposed an alternative classification system to the traditional one outlined above. The new system separates prevention efforts into three levels: universal or public health measures (directed at everyone in the population); selective (for a subgroup who may have an above average risk of developing obesity); and indicated (targeted at high risk individuals who may have a detectable amount of excess weight which foreshadows obesity (see Fig. 1). In this scheme, prevention is used to describe only those actions that occur before the full development of the condition. Many actions concerned with reducing the disability associated with obesity, previously classified as tertiary prevention, are redefined as maintenance interventions.

Indicated prevention Indicated prevention deals with individuals who are already overweight or showing biological markers associated with excessive fat stores but who are not yet obese. These are high risk individuals in whom failure to intervene at this stage will result in many becoming obese and suffering the associated ill health consequences in the future.

Fig. 1 Levels of prevention measures.This diagram represents the three complementary levels of preventive actions from the very specific indicated prevention approach, to targeted preventive actions and the broader universal or populationwide prevention programmes. Adapted from Institute of Medicine, 1994.

362

tntflcated prevefiflon (Tnoeb ttxno wtftti aoafing weight problems)

Bnhsh Medico/ Bulletin 1997^3 (No. 2)

Prevention of obesity

The identification of people who are likely to benefit from indicated prevention programmes should be a component of all clinical assessment protocols in routine health care. Regular determination of body weight and the calculation of body mass index (BMI) identifies patients who have made substantial gains in weight over a short period of time or whose BMI is already at an unhealthy level. In addition, measuring blood pressure and biochemical parameters (such as blood lipids and blood glucose) will indicate when the excessive adiposity is beginning to impact on health. The recently released Scottish Intercollegiate Guidelines Network (SIGN) report for the management of obesity in Scotland13 recommends regular screening of body weight and waist measurement. The guidelines suggest that patients should be recruited into indicated preventive programmes through self-referral, practice audit or opportunistic screening. Individuals from families with a history of obesity, or who come from one of the high risk groups or vulnerable periods of life identified in Tables 1 and 2 should be particular targets of these preventive measures. Overweight children ought to be a major focus of such programmes. Indicated prevention strategies usually involve working with patients on a one-to-one basis or, alternatively, through the establishment of special groups to provide guidance and support. Patients recruited to indicated prevention programmes will already be demonstrating some weight-related problems. Thus, the primary objectives of this preventive strategy are restricted to preventing further weight gain and reducing the number of people who develop obesity-related comorbidities. In particular, indicated prevention aims to prevent overweight children from becoming obese adults.

Selective prevention

Selective prevention measures are aimed at sub-groups of the population who are at a high risk for the development of obesity. High risk subgroups possess a biological, psychological or socio-cultural factor which has been associated with increased risk for obesity and are identified in Tables 1 and 2. This risk may be acute, as in the case of certain vulnerable life stages, or it may be a life-long concern such as a genetic predisposition to weight gain. In contrast to the individual patient focus of indicated prevention, selective prevention strategies are directed mostly at groups. These may be initiated through schools, colleges, work sites, community centres and Bntith M,d,cal Bulletin 1997;53 (No. 2)

363

Obesity

Table 1

Vulnerable periods of life for the development of future obesity

Vulnerable period

Reason for increased risk

Pro-natal

There is evidence to suggest that Fatal nutrition and in-utero development has permanent effects on later growth, body shape, fatness and energy regulation8*'9*

Adiposity rebound (5—7 years)

Body mass index begins to increase rapidly after a period of reduced adiposity during pre-school years. Food and activity patterns often change as a result of exposure to new environments and patterns of behaviour conducive to the development of obesity may develop. Earty and rapid adiposity rebound indicates increased risk of persistent obesity later in life 99 ' 100

Adolescence

Period of increased autonomy which is often associated with irregular meals, changed food habits and periods of inactivity during leisure combined with physiological changes which promote increased fat deposition, particularly in females 9010 '

Early adulthood

Early adubhood usuaOy correlates to a period of marked reduction in physical activity. In women this usually occurs between the ages of 15—19 years but in men it may be as late as the early 30s 9 ' Although on average, women gain less than one kilogram after each pregnancy102, excessive weight

Pregnancy

gain during pregnancy may result in increased retention of weight after delivery, particularly with early cessation of breastfeeding. This pattern is often repeated after each pregnancy92 Menopause

In Western societies, weight generally increases with oge but it is not certain why menopausal women are particularly prone to rapid weight gain 93 . The loss of the menstrual cycle does affect food intake and reduce metabolic rate slightly but reduced acrivHy may account for the greatest proportion of this weight gain 103 .

Table 2

Identifying groups at high risk of weight gain

High risk groups

Reason for increased risk

Genetically susceptible individuals

There is no longer any doubt that, given the same environment, some individuals are more prone to depositing fat. The basis of these deferences in individual susceptibility to obesity is yet to be fully elucidated but is believed to involve a number of physiological processes associated with fat deposition, oxidation and involuntary energy expendrturefi.

Certain ethnic groups

In many countries, certain ethnic groups appear to be especially prone to the development of obesity. This is believed to be the result of a genetic predisposition to obesity which becomes apparent when such groups are exposed to diet and lifestyle patterns conducive to weight gain (e g. IrxJkm immigrants to the United Kingdom95).

Socially or economicalfy disadvantaged

In the United Kingdom and other European countries, there is an inverse association between income and education level and obesity which is most pronounced among women and children It is argued that cheaper foodstuffs are usually high in fat and energy dense, and those with less financial resources spend more time in sedentary activities such as watching TV 94 ™.

Recent successful weight reducers

Successful weight reduction is usually followed by the regain of one-half to one-third of the weight losi over the following year 1Oi . It is believed that biological and behavioural processes act to drive body weight back to baseline levels91.

Recent past smokers

Smokers are usually thinner than non-smokers because smoking tends to depress appetite, increase the basal metabolic rate and, after each cigarette, induce a surge in heart and metabolic rate 97 . Mean weight gain attributable to smoking cessation has been found to be on average 2.8 kg in men and 3.8 kg in women but heavy smokers (more than 15 cigarettes per day) and younger people tend to gain much more 100 . However the health benefits of smoking cessation far outweigh the healthrisksof any subsequent weight gain.

Patients who have been prescribed certain drugs that promote weight gain

A number of classes of drugs are known to promote weight gain mostly through encouraging excessive food intake, often at times of enforced inactivity. Corticosteroids, sulphonylureas, Insulin, (5adrenergic blockers, some steroid contraceptives, gortrogens and other drugs have been associated with weight gain.

364

British Medical Bulletin 1 9 9 7 ^ 3 (No. 2)

Prevention of obesity

shopping outlets as well as primary care settings. Selective prevention is concerned with improving the knowledge and skills of groups of people to allow them to deal more effectively with the factors which put them at a high risk of developing obesity. Universal or public health prevention

Universal prevention programmes are directed at the population or community as a whole regardless of their current level of risk. Such a mass approach to the control and prevention of lifestyle diseases is not always appropriate and has been criticised for requiring those who may be at low risk to make similar changes to those at high risk14. In the prevention of overweight and obesity, however, where the prevalence of the condition is already extremely high and a large proportion of the population is at high risk, universal approaches have the potential to be the most cost effective form of prevention15. Universal prevention aims to stabilise the level of obesity in the population, to reduce the incidence of new cases and, eventually, to reduce the prevalence of obesity. However, in line with other public health approaches to disease control, the most important issue in dealing with a problem of extremes in weight is a reduction in the mean weight of the population. The association between the mean level of BMI and the prevalence of obesity is discussed later in the chapter. Other objectives of universal prevention include a reduction in weight-related ill health, improvements in general diet and exercise levels and a reduction in the level of population risk of obesity.

Integrating prevention into management The reluctance of the medical profession to take up the issue of obesity prevention has been ascribed to: (i) a misunderstanding of the relationship between weight and health; and (ii) a conviction that, given their limited time and health promotion skills, their role is best limited to therapeutic interventions16. There has been much controversy over the relationship between body weight and total mortality. Many studies have shown a U or J shaped association between the two, with higher mortality rates at both upper and lower body weights, and where substantial increases in relative risk for mortality do not occur until a BMI around 27-28 kg/m2 is reached17"19. As a result, many health professionals have argued that intervening to control weight gain at levels much below a BMI of 27 kg/m2 is actually counterproductive to health20-21. However, recent re-analyses of these BHHth M,d,cal Bulletin 1997;53 (No. 2)

365

Obesity

All women (4726 deaths)

Worn en who raw tm oK«d CM99 deaths) Women who raw smoktd and recently had ttablewdght (531 deaths)

. 1.0

^

~