Obesity is a global threat to public health, and the proportion of children, adolescents and adults with obesity has been increasing rapidly over recent decades; although at the moment it appears that development has stagnated in most countries. In Denmark, 11-16% of all children in pre-school age are overweight, while the prevalence of Danish teenagers is 19-25%. It is very important that the WHO, the American Medical Association (AMA) and the Canadian Medical Association (CMA) have declared obesity as a disease in 1948, 2013 and 2015, respectively.
There are 20 internationally recognized medical and psychosocial obesity related complications in childhood, where especially high blood pressure, high cholesterols, liver fat and type 2 diabetes mellitus cause significant morbidity and mortality later in adulthood. These conditions were seen primarily earlier in adults, but are now also seen to a considerable extent in childhood. For example, approximately 51% of children and adolescents with overweight or obesity exhibit borderline or overt elevated blood pressure, 27% exhibit elevated cholesterols, 31% exhibit fatty liver, 74% exhibit elevated fat in the muscles, 18% exhibit prediabetes, and 50 % exhibit sleep apnea. Further, later in adulthood more than 20 cancers are associated with obesity.
In addition, psychological stressors interact with obesity. These, for example, manifest themselves in terms of reduced quality of life, where children with have been shown to have a quality of life similar to children suffering from cancers, and have a pronounced tendency of loneliness, feeling of shame, or depression.
Numerous studies have shown that childhood obesity exhibit a clear hereditary component. This is shown, among other things, by studies of adopted children which displays a weight profile closer to their biological parents than their adopted parents. This clearly shows the importance of how genetics influence the child compared to environmental effects.
The recent years of progress in mapping the human genome have increased the scientific focus on hereditary forms of obesity. Several major studies have identified hereditary variations of importance for the development of obesity, and it is believed that 50-70% of the degree of fat mass is correlated to human genes. However, it is only a small part of the genes, which alone can explain the degree of obesity.