[Obesity: a model of complex interactions between genetics and environment].

Obesity is explained by the joint actions of genetic susceptibility and environmental factors, such as a westernized lifestyle (sedentary lifestyle, calorie-dense foods), inducing an obesogenic environment. The search for obesity susceptibility genes remains complex, despite recent adavances made in the obesity genetics field. Except very rare monogenic type obesity, common obesity is thought to be polygenic and the genetic contribution to interindividual variation in common obesity has been estimated at 40-70 %. The genome-wide association studies have led to identify numerous genetic loci associated with body mass index and obesity risk. However, the predictive value of these loci to the obesity risk at the population level remains low. Finally, the influence of environmental factors on genetic susceptibility to weight gain is also related to epigenetic factors. Nutritional unbalance during fetal development may change the intrauterine environment and lead to altered gene expression (fetal programming) with alterations in DNA or histone methylation resulting in an increased susceptibility to chronic disease in adulthood, such as obesity.