At its simplest level, obesity is a disease of energy imbalance. To maintain a healthy weight, energy from fuel taken into the body as food needs to balance with the amount of energy expended by the body in daily activities. Obesity can develop when the energy scales are tipped in favour of available energy. In reality, obesity is a much more complex and multifactorial disease, arising through the interaction of metabolic, genetic, behavioural and environmental factors.

The social changes that have occurred over the last few decades are thought to explain the marked increase in the prevalence of obesity. Technological advances in the workplace and at home, the popularity of computers and labour-saving devices in this new millennium mean that we are all much less active in the course of our everyday lives.

Besides a decrease in activity levels, the availability of energy-dense foods in abundance is also considered to be a key contributory factor. There has been a move away from the traditional diet to an increase in the use of convenience foods (with an associated decrease in cooking, menu planning and shopping skills), as well as an increase in the consumption of snacks and soft drinks (biscuits, cakes, chocolate, crisps and fizzy drinks). There has also been significant growth in the UK market for fast food and take-away outlets (www.marketresearch.com). Food portion sizes in restaurants, take-aways and snacks have increased markedly over the past decade and research shows that individuals inevitably consume greater energy when presented with larger portions at mealtimes.¹¹

Typical weekly chores and the calories expended in the 1950s compared with 2000

Adapted from Costain, 2003 ¹²

The increase in the prevalence of obesity makes it evident that on a population level energy intakes have not been appropriately adjusted to correct for this reduction in ‘spontaneous’ activity.