Which are the known causes and consequences of obesity, and how can it be prevented?

Summary of a HEN network member’s report

The issue

The percentage of people with obesity (body mass index >30) has increased markedly in many countries. This trend has been observed in most European countries, North America, and several South American and Asian countries. In many of these countries the number of obese people has more than doubled during the past 20 years. In the United States, the total percentage of the population with obesity is more than 20%, while the rates in England, Germany and Poland exceed 15%. The increased prevalence of obesity applies to both men and women in all age groups (children and adults).


The development of obesity depends on both genetic factors and environmental factors. In genetically predisposed individuals, lifestyle factors (such as diet and exercise) and social, behavioural, cultural and community factors determine whether or not obesity develops. Obesity increases the risk for many serious diseases, e.g. diabetes, cardiovascular diseases and joint diseases. The association between obesity and some cancers is strong. Obesity also has a strong negative impact on quality of life.

The costs to society of obesity and diseases associated with obesity are high. Information about the cost–effectiveness of different methods of combating obesity is, however, limited. The cost–effectiveness of preventive methods cannot be calculated due to uncertainty concerning the results. Among treatment methods, the costs of achieving weight loss are relatively low for dietary counselling, behavioural therapy, dietary replacement formulas with low-energy content, and surgical treatment, but considerably higher for pharmacological treatment. The evidence on the treatment of obesity shows the following.

  • Changing dietary habits through counselling (mainly to reduce energy and fat intake) can lead to weight loss, as a rule 3 kg to 10 kg during the first year (or 10% of body weight in children). The long-term effects are uncertain.
  • Regular exercise contributes to weight reduction.
  • Behavioural therapy in conjunction with changes in diet and exercise can improve results if the supportive interventions are continued for a longer period.
  • The Weight Watchers approach achieves a permanent loss of 10% or more of starting weight in about 20% of those who attend all sessions.
  • VLCD (or very low calorie diet, achieved through use of a protein-rich formula) for 6 to 12 weeks yields a greater weight loss than a conventional low-energy diet. In studies of VLCD for one to two years, during which treatment is often periodic, researchers have noted that maintained weight loss was a few kilograms more than in treatment with a balanced diet alone.
  • Pharmacological treatment with orlistat or sibutramine yields an average 2 kg to 5 kg weight loss beyond that achieved with diet and exercise counselling alone. In clinical trials, one fourth to one fifth of those who started pharmacological treatment lost at least 10% weight, compared to half as many in the group receiving placebos.
  • Surgical treatment, which can be appropriate for patients with severe obesity, lowers weight on average by more than 25% (e.g. from 125 kg to 90 kg) up to 5 years after surgery. After 10 years, the retained weight loss is approximately 16%, or on average somewhat more than 20 kg. Surgical intervention carries some risk for complications.
  • Alternative medicine methods have shown no reliable evidence of having any effect on obesity.

Policy considerations

Most population-based prevention programmes that have been scientifically assessed have not shown any favourable effect on the prevalence of obesity. However, examples exist of programmes for both adults and children that have been successful, at least in the short term. New strategies to disseminate knowledge about the causes and risks of obesity and to change dietary habits and motivate people to increase physical activity need to be developed and assessed. Concurrently, there is a need for policy interventions at the societal level to reduce the prevalence of obesity.

The risks related to obesity can be reduced through weight reduction, regardless of the methods used. Even if weight reduction is not successful, the risks associated with obesity can be reduced by increased physical activity, smoking cessation, and improved control of diabetes, high blood pressure and elevated blood lipids.


Östman J, Britton M, Jonsson E, eds. Treating and preventing obesity: an evidence based review. The Swedish Council of Technology Assessment in Health Care (SBU). Weinheim, Wiley-VCH, 2004.