The wider causes and risk factors

Although on a simple level obesity occurs when energy intake is greater than energy output, it is a complex condition and it is sometimes difficult to determine why one person becomes obese while another does not.

Genetics and human evolution

Human history is one of being hunters when food was scarce and of efficiently storing energy as fat when food was available.  Humans no longer live in an environment where food is scarce or sporadic and where activity is necessary. The genetic adaptation to our environment occurs very slowly and is around 25,000 years behind changes in the environment. Thus, our genetic profile has hardly changed since the time we were active hunters. Given this imbalance between our modern lifestyle and our ‘ancient’ genetic profile, it is not surprising that it is quite easy for many people to gain weight. Human obesity has a major genetic component, which varies markedly between individuals.  In most cases, obesity is attributable to multiple genes that individually have only small effects and interact variably with environmental factors.  The dramatic increases in the prevalence of obesity over 50 years or less must be related primarily to changes in lifestyle, as the gene pool will have barely changed during this period.  At the same time, however, many individuals have remained lean, suggesting that specific features of their energy balance mechanisms can effectively protect them against obesity.

Individual behaviour

Cognitive factors, such as knowledge, attitude, self-efficacy and intention to change, are important in health behaviour, but have a less clear role in nutrition and physical activity than for instance smoking and safe sex. Some people have successfully prevented and treated weight gain in themselves with behavioural methods, but most who have lost weight succeed in keeping it all off only temporarily. Scientists continue to study how to influence such behaviour and how to help people maintain a significant weight loss, but believe tackling the wider environment is crucial to reversing the epidemic.

The obesity-promoting society

In explaining the increasing obesity epidemic, more emphasis is being put on the changing environment. At the end of the former millennium, experts labeled the environment ‘obesogenic,’ indicating that the environment facilitates too much high-energy consumption and too low an activity level, too easily.