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Background

  1. Top of page
  2. Background
  3. Basic science
  4. Behavioural science
  5. Prevention
  6. Treatment
  7. Policy implications
  8. References

Obesity is not new (1) but it is a growing problem. While the mean body mass index (BMI; a measure of relative weight) of the population has been steadily increasing among adults over many generations, there has been a concomitant increase in the proportion of the population who are seriously obese. The latest World Health Organization estimates are that around 1.2 billion people in the world are overweight and at least 300 million of them are obese. The UK is fortunate to have year-on-year surveys that track the increasing prevalence of obesity. In 2004, 23.6% men and 23.8% women were obese and this is predicted to increase to around 33% and 28% by 2010. Additionally, the problem is penetrating into childhood, rising from 1.8% to 6.0% in boys and 1.3–6.6% in girls aged 5–10 years between 1974 and 2002/03 (2) and estimated to reach around 19% and 22% in boys and girls respectively by 2010. This, together with a greater recognition of the burden of disease and the health costs associated with obesity (especially abdominal obesity) including increased risk of coronary heart disease, type 2 diabetes and cancer (3), has taken the problem outside the traditional health/research sector and into front-line politics as a debate over roles and responsibilities rages (4).

This overview draws on 34 ‘State of the Science’ review papers commissioned as part of the UK Foresight project ‘Tackling Obesities: Future Choices’. It explores the many facets of the issue from genetics to social norms and ethics from the perspectives of national experts, with resonances on an international scale. The conclusion is inescapable. Obesity is a complex, multifaceted problem with no easy or obvious solutions. Subsequent steps in the Foresight process will seek to provide clarity to this complexity through the use of an obesity systems map and will explore the environment for action through the development of a range of future scenarios. These two strands of qualitative work will inform estimates of possible future obesity levels using a newly developed quantitative cell-based model.

Basic science

  1. Top of page
  2. Background
  3. Basic science
  4. Behavioural science
  5. Prevention
  6. Treatment
  7. Policy implications
  8. References

At the heart of the problem of excess weight is a homeostatic biological system, struggling to cope in a fast-changing world, where the pace of technological revolution outstrips human evolution. Since the identification of the ob gene in 1994, research into physiological mechanisms controlling body weight has grown exponentially (5–9) including work on inter-generational effects and impact of early-life experiences that may perpetuate obesity within families (10,11). Much has been learnt about regulatory mechanisms from animal models, with the potential to perform detailed investigations, including the use of transgenic models (7). This work continues to provide critical underpinning for the development of novel drug targets for the treatment (and perhaps in the future, prevention) of obesity and/or the modulation of related metabolic disorders (5,6,8).

Intriguingly, most of the significant advances in understanding have occurred in relation to the control of food intake. Indeed, research into the metabolic aspects of energy expenditure has yielded little evidence of abnormalities (12), although this does not rule out future therapeutic interventions. But in contrast, studies of the regulation of food intake have spawned new components to the human appetite regulation system at an impressive rate. This includes work on single gene defects associated with severe obesity that have highlighted critical neural pathways, especially in relation to leptin and the melanocortin system (5). Other research has shown the importance of peripheral signals derived from adipose tissue and the gut (6). New research is considering the interactions between food and biology through studies of the neural response to food-related stimuli (9). This fusion of psychology and biology provides important insights into mechanisms underpinning food habits.

However, individual strands of this basic biological research are often conducted in isolation and this limits a fuller understanding of the relative importance of different pathways, their interactions and redundancies within the system. Thus, it is still difficult to reliably predict the key points for intervention. This is further compounded by the inter-individual variability in each of these components and research into gene–environment interactions is in its infancy (5). However, this is a topical area of research, in the public and private sector, not least with respect to developments in nutri-genomics, the science underpinning the concept of personalized nutrition (13).

Behavioural science

  1. Top of page
  2. Background
  3. Basic science
  4. Behavioural science
  5. Prevention
  6. Treatment
  7. Policy implications
  8. References

In spite of this mechanistic complexity, obesity is ultimately a consequence of a long-term uncoupling of energy intake and expenditure. Observational studies of human behaviour have sought to elucidate the detailed components of this dysregulation but are hampered by the lack of robust, objective measures of dietary intake and physical activity in large populations (14,15). There has been disproportionate attention given to debates over the relative importance of diet or inactivity in the aetiology of obesity, given that the subtle shifts in energy balance which have occurred at a population level are below the limits of detection of current methodologies. In the case of dietary intake, long-term records are based on household food purchases while historical data on physical activity are totally lacking. However, recent technological developments in the measurement of activity levels have given rise to a raft of new studies to consider the variation within a population with respect to physical activity and subsequent risk of obesity, and this is yielding important insights. For example, showing that sedentary behaviours, especially television viewing, are critical risk factors for obesity and the importance of energy expended during routine daily activities as a contributor to overall energy expenditure, which has clear implications for transport policies and other aspects of the built environment (15,16). In modern societies, overt exercise accounts for a very small proportion of total energy expenditure and is likely to play only a minor role in preventing obesity, although positive benefits on wider disease risk should not be ignored (12).

Measuring dietary intake outside the laboratory remains problematical, but by combining data from experimental, observational and controlled intervention studies, a number of specific dietary risk factors have been identified including a high energy density, characterized by a diet high in fat and low in fibre and the consumption of sugar-rich drinks, each compounded by large habitual portion sizes. These provide promising targets for intervention and are consistent with other strategies for the prevention of chronic disease (14). This offers potential opportunities for interventions by the food industry through reformulation of existing products and innovation with healthier options, tailored to meet the nutritional needs of a largely sedentary population (17).

Research into the physiological systems controlling body weight is vital but it is increasingly recognized that biology operates within a social and cultural context (18–20). The choice of lifestyle for the population at large, or individuals, is neither a pure product of genetics nor freewill, but a melting pot, heated and stirred by the influence of the wider environment. Understanding these wider determinants of food intake and physical activity is a key area of research, spanning across areas as diverse as family dynamics, school policies, urban design and media influences (16,18,21,22). Most of this work is presently conducted at a population level and more investigation at an individual level is warranted to explain the inter-individual variability in obesity rather than overarching population trends (18). A focus on socioeconomic and ethnic disparities will help to bridge the widening health inequalities (23). However, population-based interventions must be sensitive to the need to promote a healthy body weight, without excessive thinness, especially among individuals predisposed to eating disorders (24).

Prevention

  1. Top of page
  2. Background
  3. Basic science
  4. Behavioural science
  5. Prevention
  6. Treatment
  7. Policy implications
  8. References

At present, the evidence base for the prevention of obesity is heavily biased towards causes rather than solutions. Data from intervention studies are few in number and limited in scope (15,25). Most are confined to controlled research settings. Few interventions have been overtly successful in reducing the prevalence of obesity and even the most promising have not been widely replicated (25). Areas identified for future development include multidisciplinary approaches (25), overcoming ambivalence to change (19), establishing new social norms, and, critically in the case of children, parental engagement (18). This is likely to require greater involvement of research partners outside traditional academic/health professional arenas. The need for large-scale studies involving diverse teams over long periods of time also challenges existing funding mechanisms and data-gathering processes (4,26).

Treatment

  1. Top of page
  2. Background
  3. Basic science
  4. Behavioural science
  5. Prevention
  6. Treatment
  7. Policy implications
  8. References

In contrast to interventions for the prevention of obesity, there have been some recent advances in treatment development. Treatment is hampered by the physiological mechanisms which favours weight maintenance. However, long-term studies of intense individual interventions show that sustained changes in diet and physical activity can lead to modest but sustained reductions in body weight, of approximately 5%, over many years, with concomitant improvements in comorbidities, especially the risk of type 2 diabetes and overall reductions in the cost of health care (27). Pharmacological interventions produce significantly greater weight loss while the treatment is continued (28). Advances in bariatric surgery means that this is now a well-recognized and effective intervention for obesity, with weight losses of 10–30% and substantial reductions in new cases of diabetes and cardiovascular mortality. However, although this is a large weight reduction for an individual, the impact on the population mean weight is small, because the number of individuals for whom surgery is appropriate is small.

At present, only a small proportion of people who are obese receive optimal care because of a lack of resources (including trained staff) and clinical management practices which prioritize the treatment of comorbidities over weight loss. There is a need to identify individuals most likely to benefit from treatment. The BMI is a useful measure for population surveillance but has limited sensitivity at an individual level. Instead, it needs to be combined with information on body fat, other risk factors including family history, to make improved risk assessments.

Future treatment-based research needs to focus on improving the success of behavioural interventions and developing new, more effective drug therapies. While there are established public–private mechanisms for investment in the latter, behavioural interventions have, historically, been poorly supported. This will not be reversed quickly given the paucity of trained researchers in this area. Importantly, treatment should not be divorced from prevention. The maintenance of weight loss and the prevention of weight regain is a critical yet under-researched component of treatment (27). In the short term, significant progress could be made by the implementation of existing knowledge.

Policy implications

  1. Top of page
  2. Background
  3. Basic science
  4. Behavioural science
  5. Prevention
  6. Treatment
  7. Policy implications
  8. References

Epidemiological analyses of the prevalence of obesity have provided a catalyst for research. Some countries have the unenviable reputation of an even greater proportion of obese people than the UK. Indeed, the prevalence of obesity in the UK has been steadily tracking that of the USA with a lag of about 10 years. Obesity levels in the USA now exceed 30%. This gives a glimpse into the future if we fail to act now. Ongoing analysis is essential for surveillance and monitoring and there is scope to refine these procedures to enhance the usefulness to researchers and policymakers through rigorous evaluation (26). Further analysis of these datasets can also inform future projections to underpin the provision of public services, including health and pensions and assess the economic implications (29). It will also assist in the development of an overarching strategy to tackle obesity (4). Our understanding of the risks of chronic disease associated with obesity suggests that even 100% success in preventing new cases of obesity among young children will leave a substantial burden of ill-health and associated costs for years to come (3). These evidence reviews suggest that long-term strategies (spanning several generations) encompassing both prevention and treatment for adults and children and which also take account of the needs of groups at different lifestages and with diverse circumstances would be most likely to be effective at tackling obesity.

However, just as obesity develops slowly, within both individuals and populations, so too will it take time to establish new habits and build new structures to support a healthy diet and enhanced physical activity. Interventions will only be effective if they are designed to have in-built sustainability. One of the important lessons from efforts to reduce smoking and alcohol is the lag time between research and action, whether among individuals, in terms of behaviour change or at a population level in terms of public health interventions. Controls on smoking provide an interesting case study with respect to the acceptability of different types of interventions (30,31). Over the last 50 years, policymakers have moved from the basic provision of information and advice, through the facilitation of healthier options (e.g. through use of nicotine replacement), active discouragement of the unhealthy behaviour (e.g. taxation, advertising restrictions) and onto regulatory action (e.g. bans on smoking in public places).

Action on diet (including alcohol) and activity is far behind, social marketing techniques will contribute to the raising of awareness, the influencing of public opinion and resetting of social norms (32). Campaigns in relation to alcohol have successfully reset social norms with respect to drinking and driving. However, this has not been accompanied by a decrease in overall alcohol intake (31). Here, as with other diet and alcohol interventions, most observers accept the need for such campaigns to coexist with parallel environmental interventions to support and facilitate behaviour change. However, it is important not to be over-reliant on a single approach (33).

These ‘State of Science’ reviews have clearly demonstrated that evidence for specific actions to tackle obesity is neither complete nor perfect and the obesity debate is fuelled by differing interpretations of the scientific literature. Meanwhile, the burgeoning prevalence of obesity, especially in children, has resulted in sustained pressure to act and to act quickly. The resulting tensions illustrate just one of the ethical challenges which arises in any strategy to tackle obesity (34). Neither is it an easy position for scientists who seek the ‘best evidence possible’, nor for policymakers who fear interventions which do not guarantee success. Greater interactions between scientists and policymakers will help to ease these tensions and maximize the potential to develop and execute effective interventions in a virtuous circle of continuous improvement which combines scientific development, policy implementation and joint evaluation.

References

  1. Top of page
  2. Background
  3. Basic science
  4. Behavioural science
  5. Prevention
  6. Treatment
  7. Policy implications
  8. References