The current obesity epidemic is known to have coincided with profound societal changes involving both physical activity levels and food consumption patterns as well as demographic and cultural changes affecting the conduct of human beings in various ways. On the other hand, obesity is a complex and multifactorial chronic disease that usually becomes manifest in child hood and adolescence. Its origin is a genetic and environmental interchange, of which environmental or behavioral factors play the most important role, stemming from an imbalance between energy intake and expenditure. Still and all, it is rather simplistic to assume that obesity is only due to excessive consumption and/or deficient physical activity levels. Currently, various lines of investigation have been initiated that evaluate the determinants of obesity, of which nutrigenomics and gut microbiota deserve special attention.