Obesity: risk factors

Obesity is a complex disease with wide ranging cause aetiology -

Obesity results from an imbalance between energy intake and energy expenditure. All other things being equal a sustained period in which energy intake in the form of food is greater than energy expenditure in the form of physical activity (and the energy requirements of basic survival) will result in an increase in weight and body mass index (BMI) and will lead to obesity. Although the relationship between energy balance and obesity is fairly straightforward, the factors underlying energy balance can be very complex, and include the following:

Physical Activity/sedentary time - Individuals that engage in little or no physical activity, particular those not acheiving the reccomendations for activity levels laid out by The Department of Health and therefore have increased sedentary lifestyles are predisposed to a greater chance of having obesity.
Sedentary Behaviour - Increased sedentary behaviour/bouts of prolonged inactivity are assoictaed with adversed outcomes and increased obesity in both, adults and children.
Genetics - there are a small number of genetic defects which lead to obesity, which can influence an individuals' metabolism and behaviour and predispose to obesity though genetic factors are unlikely to explain the large increases in obesity in recent years.
Environment - populations that exist in environments where there is easy access to cheap tasty food are likely to show a greater prevalence of obesity. Likewise where energy-saving technology exists (cars, washing machines etc.) the energy expenditure in physical activity is likely to be low, pre-disposing to obesity.
Increasing age - there tends to be a 'natural' increase in weight and the prevalence of obesity with age (although this again relates to energy balance, and in theory at least there is nothing inevitable about this increase).
Ethnicity - some ethnic groups are more predisposed to obesity, e.g. women of Afro-Caribbean origin are more likely to be obese.

A more detailed examination of risk factor for obesity is available from the Foresight Tackling Obesities: Future Choices project (2007) (project report and research reviews).