[From obesity to obesities: from concepts to practices]

In the singular, obesity is a symptom reflecting an excess of energy stores as fat mass, the only trait obese people are sharing. Long time ago we proposed to use the plural to account for the large diversity characterizing obese subjects that conceptual evolutions have put to the fore during the past three decades. Weight gain and obesity are resulting from a positive energy balance produced by the conjunction of a number of etiopathogenetic factors associated in various proportions according to patients and evolutive status. Decreasing physical activity, increasing sedentarity, quantitative and qualitative energy consumption unadapted to energy expenditure and to lipid oxidation capabilities, reinforced by psychological needs, are catching out the control of food intake, particularly since it is more efficient to defend against famine than to protect against plethora. These environmental factors, responsible for obesity pandemia, lead to obesity subjects predisposed by their genetic background, in itself extremely variable. The clinical heterogeneity of obesity is patent and a careful phenotypic analysis is a prerequisite to design the management strategy. Obesity is a chronic situation that needs a long-term treatment. The goals of treatment cannot be longer reduced to weight loss only, which in addition should be realistic, i.e. moderate. Management strategies must be conceived on a long-term basis, focused on prevention of weight regain, multifaceted and individually tailored. A number of tools are available and the state of the art is to use them appropriately to avoid being counter productive. Obesity may be viewed as an adaptive symptom in subjects poorly prepared to cope with recent environmental changes, but it is also a disease due to its prevalence, the number of weight dependent comorbidities and its socio economic costs. A specific medical approach of obesity has still to be developed.