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A well-resourced, comprehensive, population-based set of strategies is needed to attenuate and eventually reverse the current trends of increasing obesity prevalence now apparent in most countries. The Epidemiological Triad (host, vector, environment) has proven to be a robust model for other epidemics and is applied to obesity. Host-based strategies are primarily educational and these tend to be most effective among people with higher incomes and higher educational attainment. The main vectors for a high-energy intake are energy-dense foods and drinks and large portion sizes and, for low energy expenditure, machines that promote physical inactivity. Vector-based strategies that alter food formulation can have a significant impact, particularly through influencing common, high-volume foods. The increasingly 'obesogenic' environments are probably the main driving forces for the obesity epidemic. There are many environmental strategies that can influence the physical, economic, policy or socio-cultural environments, but the evidence base for these potentially powerful interventions is small. Children should be the priority population for interventions, and improving the general socio-economic conditions for disadvantaged, marginalized or poor population sectors is also a central strategy for obesity prevention. The key settings for interventions are schools, homes, neighbourhoods, primary health care services and communities. The key macroenvironments for interventions are the transport and infrastructure sector, the media and the food sector.

The increasing prevalence of obesity in many countries means that it should now be considered a pandemic. 1 One estimate from Australia suggests that over the past decade the average adult has been adding 1 gram a day to body weight. 2 This has occurred in the face of increasing knowledge, awareness, and education about obesity, nutrition, and exercise. It has been suggested that a paradigm shift is necessary if future progress is to be made. 3 Traditionally, weight gain was thought of as caused by eating too much or exercising too little, or both (changes in weight = energy intake − energy expenditure). This led to the search for small deficiencies in energy metabolism such as a reduced thermic effect of food to explain obesity. 4 Treatment was dominated by calorie counting, and public health messages extolled people to balance their intake and output. This paradigm has changed with the increasing understanding of the dynamic relations between energy stores, appetite mechanisms, and energy metabolism and of the wider recognition of nutrient partitioning. 5 6 From studies which have shown that fat balance is equivalent to energy balance, 7 the fat balance equation was developed (rate of change of fat stores = rate of fat intake − rate of fat oxidation). 5 This equation is more dynamic than the original static equation and reflects energy balance under normal conditions of free access to foods. Because fat intake and oxidation are not closely balanced, 8 this approach does not need metabolic abnormalities or genetic mutations to explain weight gain. Indeed, the differences in body fat between people living in the same environment could be better described as normal physiological variation. This paradigm is more helpful in explaining changes in body fat within an individual over time, but it does not account for the wider influences within and around individuals on obesity.

There has been, and continues to be, widespread international concern about athletes' use of banned performance enhancing drugs (PEDs). This concern culminated in the formation of the World Anti-Doping Agency (WADA) in November 1999. To date, the main focus on controlling the use of PEDs has been on testing athletes and the development of tests to detect usage. Although athletes' beliefs and values are known to influence whether or not an athlete will use drugs, little is known about athletes' beliefs and attitudes, and the limited empirical literature shows little use of behavioural science frameworks to guide research methodology, results interpretation, and intervention implications. Mindful of this in preparing its anti-doping strategy for the 2000 Olympics, the Australian Sports Drug Agency (ASDA) in 1997 commissioned a study to assess the extent to which models of attitude-behaviour change in the public health/injury prevention literature had useful implications for compliance campaigns in the sport drug area. A preliminary compliance model was developed from three behavioural science frameworks: social cognition models; threat (or fear) appeals; and instrumental and normative approaches. A subsequent review of the performance enhancing drug literature confirmed that the overall framework was consistent with known empirical data, and therefore had at least face validity if not construct validity. The overall model showed six major inputs to an athlete's attitudes and intentions with respect to performance enhancing drug usage: personality factors, threat appraisal, benefit appraisal, reference group influences, personal morality and legitimacy. The model demonstrated that a comprehensive, fully integrated programme is necessary for maximal effect, and provides anti-doping agencies with a structured framework for strategic planning and implementing interventions. Programmes can be developed in each of the six major areas, with allocation of resources to each area based on needs-assessment research with athletes and other relevant groups.