The worldwide rise in body weight has reached epidemic proportions and this has serious public health consequences. Despite the universal recognition of this problem, its causes are still debated: some attribute it to excess caloric intake; others blame a lack of physical activity (PA); some implicate specific changes to micro- and macro-nutrients. During the past century, government health agencies have developed guidance on healthy eating. These, along with advances in agriculture and food manufacturing, have largely eliminated nutrient deficiencies and helped reduce the consumption of fat. Over the past 60 years, however, technological advances and shifts in the types of occupations prominent in industrialised as well as developing countries have resulted in well-documented decreases in energy expenditure. Energy intake must be balanced with energy expenditure in order to prevent weight gain, and there is increasing evidence that this balance must be at a relatively high level of energy flux. A programme that was started in São Paulo in 1996 known as 'Agita' has sought to motivate populations to engage in small amounts of physical exercise daily to tackle growing obesity levels. This multi-agency initiative is one example of how to successfully increase exercise within a community and scale both within (e.g. all states in Brazil) and across many nations. Reducing caloric intake in whole populations is challenging especially at relatively low levels of energy expenditure, and evidence suggests that there is a critical energy flux threshold for regulating intake to achieve energy balance. Increasing PA, however, may be more achievable than reducing intake. Activity raises caloric expenditure and can offset excess intake. The implementation of programmes to achieve greater PA is therefore vital if the worldwide rise in body weight is to be halted, while we also need to implement programmes to help people eat smarter.
Keywords: Physical activity; diet; energy balance; energy expenditure; energy flux; energy intake; guidelines; obesity epidemic; overweight.