N° 140
20 February 2002 


In both industrialized and industrializing countries, overweight and obesity have become increasingly common over the last two decades, and in western countries it has reached epidemic dimensions. In the USA, one quarter of Americans were overweight in 1978, and in 1990, one third were overweight. The latest figures show that 60% are now overweight. In Europe, about half the adult population is currently overweight, and urban areas of many developing countries have a similar prevalence.

Overweight measurement is provided by the body mass index (BMI), calculated by dividing the body weight (in kg) by the height squared (m2). Thus, an adult who weighs 100 kg and is 2 m tall has a BMI of 25. The World Health Organization considers a BMI of less than 18.5 to be an indicator of underweight, whereas a BMI >25 indicates overweight and >30, obesity. The normal, desirable range is from 18.5 to 25. For an adult of 1 m 75, therefore, this weight range would be from 57 to 77 kg. (Height: 5ft 7in., weight range from 125.6 lb- 169.7 lb).

The reasons for the epidemic are not hard to discover. The fundamental causes of the obesity and overweight lie in sedentary lifestyles and over-consumption of high-calorie food. Body fat is a consequence of an imbalance between calorie intake and expenditure, both of which have strong cultural and behavioural components. The importance of physical activity as a determinant of body weight is well known. Children in western countries are less physically active than in the past, both at home and at school.

The consequences of the epidemic of overweight and obesity are now being realized. Overweight and insufficient physical activity are associated with several chronic illnesses, including cardiovascular disease and adult-onset diabetes. Their role in cancer development was evaluated by a panel of international experts convened by the International Agency for Research on Cancer, of the World Health Organization (WHO) in Lyon on 13–20 February 2001.

The full review and conclusions of the relevant scientific information, and recommendations for public health action have now been published in Volume 6 of the IARC Handbooks of Cancer Prevention. The IARC Handbook also summarizes the evidence of mechanisms involved in such effects, e.g., as related to hormonal metabolism and immune function.

Limiting weight gain reduces the risk of postmenopausal breast cancer and cancer of the colon, endometrium, kidney (renal-cell) and adenocarcinoma of the oesophagus. Regular physical activity reduces the risk of breast and colon cancer, and possibly that of endometrial and prostate cancer. Some of these effects are independent of that of weight control.

The increase in cancer risk is approximately linear with increasing body-mass index and decrease with increasing physical activity (whether in intensity, frequency or duration). Scientists have estimated that up to one third of cancers of the colon, breast and kidney can be attributed to overweight and insufficient physical activity. Thus, adiposity and inactivity represent the most important avoidable causes for these cancers. In the European Union, 21 000 cases of colon cancer and 13 000 cases of breast cancer could be avoided annually by maintaining a normal body weight.

There is no simple solution to the epidemic of obesity and physical inactivity. Their origins lie in culture and society, and they are epitomized by the suburban mall, with their drive-through fast-food restaurants. Dealing with it requires action at the levels of public health policy (with respect to nutrition and physical activity) and education (of both the public and health care providers). The IARC Handbook recommends maintaining body weight in the lower part of the desirable range (body-mass index between 18.5 and 25), avoiding more than 5 kg weight gain during adult life and decreasing weight (5-10%) in already overweight or obese subjects. Individuals should also be encouraged to perform moderate activity such as brisk walking and cycling, for at least 30 min several days a week. In addition to reducing the risk of chronic diseases such as coronary heart disease and diabetes, such behavior would also protect against some cancers, particularly against colon and breast cancers.

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