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The Foresight report refers to a “complex web of societal and biological factors that have, in recent decades, exposed our inherent human vulnerability to weight gain”, and presents an obesity system map (above) with energy balance at its centre and over 100 variables directly or indirectly influencing this energy balance; grouped in 7 cross-cutting themes (below):
- Biology: an individual's starting point - the influence of genetics and ill health;
- Activity environment: the influence of the environment on an individual’s activity behaviour, for example a decision to cycle to work may be influenced by road safety, air pollution or provision of a cycle shelter and showers;
- Physical Activity: the type, frequency and intensity of activities an individual carries out, such as cycling vigorously to work every day;
- Societal influences: the impact of society, for example the influence of the media, education, peer pressure or culture;
- Individual psychology: for example a person’s individual psychological drive for particular foods and consumption patterns, or physical activity patterns or preferences;
- Food environment: the influence of the food environment on an individual’s food choices, for example a decision to eat more fruit and vegetables may be influenced by the availability and quality of fruit and vegetables near home; and,
- Food consumption: the quality, quantity (portion sizes) and frequency (snacking patterns) of an individual’s diet.
Purpose of causal loop models
The Foresight team note  that a causal loop model is a device to describe the systemic structure of a complex problem. As such, it serves three very general purposes:
- to make sense of complexity. Individuals who have been deeply involved in the construction or study of a causal loop model will appreciate its considerable heuristic power. In particular, once the top-level architecture of a model (rather than its fine detail) has been thoroughly absorbed, it becomes a powerful filter for identifying relevant variables and an aid to thinking about the issue.
- to communicate complexity. The anatomy of a system map – particularly with a fairly large number of variables and many causal linkages between them – is a clear confirmation of the inescapably systemic and messy nature of the issue under study. This approach highlights the need for broad and diversified policies or strategies to change the dynamics of the system.
- to support the development of a strategy to intervene in a complex system. Careful study of a causal loop model will reveal features that help in deciding where to intervene most effectively in the system. These features are: leverage points, feedback loops and causal cascades.