Overweight has become a worldwide epidemic, not only in industrialised countries, but also in developing ones where problems of malnutrition go hand in glove with high percentages of obesity. The rates are currently rising at an alarming pace. In Spain some 15% of the population suffer from obesity and 54% from an excess of weight. Rates are going up because of the imbalance between ingestion and calorie consumption - due both to the growth and proliferation of unhealthy eating habits and an increase in sedentary life habits and styles. One of the main problems in Western society is the rise in infant obesity the incidence of which has now reached that of obesity amongst adults. It is known that a very high proportion of these children will be obese when they become adults. Treatment is complicated and so we have to take action on prevention and on encouraging healthy lifestyles and habits in the home, at school and so on. Overweight produces significant changes in health, particularly those of a cardiovascular nature such as high arterial (blood) pressure, cardiopathy and ischemia; but also problems of a metabolic nature such as diabetes type 2 and changes in blood fat, apnea during sleep, alterations in the joints, and so on. Obesity is also involved in changes in hepatic function – as a consequence of the infiltration of fat, the liver deteriorates and may end up with hepatic cirrhosis. Society at large is aware that obesity is damaging in these ways to our health. What has not been known to date is that it is associated with certain cancers. This is important, for example, for women with a family history of breast cancer – obese members of these families are more likely to contract the disease. Apart from clinical pathologies overweight causes psychological problems of self-esteem, symptoms of depression, anxiety, and so on. Thus, dealing with and treating all these means high health costs.