The prevalence of obesity is increasing in an alarming way, while that of other risk factors (hyperlipaemia, arterial hypertension.) are tending to diminish. Amongst all of the factors involved in its development, two are outstanding because of their potential for modification: an excessive calorie intake and a sedentary life style, in spite of the recommendations in favour of regularly practising physical exercise. The principal problem in studying the prevalence of obesity is the scarcity of studies that analyse it in a global form. In 1989 the first results of the MONICA project of the WHO were published, with the observation that the prevalence was higher for men than for women, and that it was greater in the Mediterranean countries and the east of Europe, in comparison with the north and centre-west. In 1997 a study was carried out by the Institute of European Food Studies (IEFS) in which 15,239 individuals participated proceeding from representative samples of the 15 Member States of the European Union. Its results showed that the higher prevalence of obesity was to be found in the United Kingdom (12%), followed by Spain (11%), while it was lower in Italy, France and Sweden (7%). By sex, the prevalence of obesity is somewhat greater amongst women, while overweightedness was greater amongst men. In Spain the distribution of overweightedness and obesity amongst the different socio-economic groups is similar to that of other regions, with the percentage of obesity being highest amongst the elderly, subjects of a lower socio-economic level and the inhabitants of the north and north-west of Spain.