Obesity: risk factors

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 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:

• Genetics - there are a very small number of genetic defects which lead to obesity, but genetic makeup in general can influence individuals' metabolism and behaviour and predispose to obesity
• 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-Carribean origin are more likely to be obese