An imbalance between energy consumption and energy expenditure

Weight gain, overweight and obesity are caused by consuming more calories than the body needs, usually by eating a diet high in fat and calories, living a sedentary lifestyle or both. The environments most people in the EU live in are increasingly obesity-favourable (“obesogenic”). There is often no need to be physically active and the availability of energy-rich food is overwhelming.

It is impossible to establish a direct causal link between environmental/cultural factors and the rise in obesity levels, but there are obvious associations between changing environments and increasing waistlines (Royal College of Physicians, 2004).

Evidence of factors that promote or protect against overweight

Based on a comprehensive review of evidence for the dietary causes of obesity, Swinburg and colleagues pointed out a number of factors that might promote or protect against overweight or weight gain (Swinburn et al., 2004). The evidence was classified as: convincing, probable, possible and insufficient. The results of the review are presented in Evidence of factors that might promote or protect against overweight or weight gain.

Major shifts in eating and physical activity patterns

The way in which work and leisure time are spent has changed, resulting in a major shift in eating and physical activity patterns:

• Jobs are more sedentary;
• Labour saving devices (lifts, remote controls) have reduced daily activity levels;
• Screen based entertainment (TV, computer) has increased;
• Less time is spent preparing meals and more processed food is consumed;
• Eating out and snacking and grazing are more common;
• Alcohol intake has increased, especially among young people.

Food advertised to children often less healthy than recommended

Food marketing and advertising reflect heavy investment and great sophistication, and permeate all levels of society. Research in the UK reveals that ninety per cent of food advertising screened during children’s broadcasts is for foods high in fat, salt and/or sugar (Royal College of Physicians, 2004). A review of the effects of food promotion to children concluded:

• Food advertising to children is extensive;
• The diet being advertised is less healthy than the recommended diet for children;
• Children enjoy and engage with food promotion;
• Food promotion is affecting preference, purchase behaviour and consumption;
• The effect is independent of other factors and operates at both brand and food category level.

Overweight is not only related to food intake and physical activity

The imbalance between calories consumed and calories burned can also be caused by other obesity-related factors. For instance, metabolism, hormones that affect the way calories are processed, and other organ systems in the body can all affect appetite or the way in which the body stores the extra energy.

As with many conditions, obesity is a result of combined influences of genetic and environmental factors. Some genetic abnormalities that predispose to obesity have been identified, but these are absent in most people with obesity.