This review aims to describe firstly, the most relevant information about the role of dietary fatty acids on cell products linked to adipocyte differentiation, genetic expression of enzymes associated to fat accretion and protein synthesis. Secondly, their effects on insulin sensitivity and insulin resistance, as conditioned by saturated or polyunsaturated fatty acids. Finally, the effects of fatty acids on substrate oxidation metabolism, particularly in relation to fat and CHO oxidation. It is presently evident that most of these effects can be modulated through dietary modifications starting with simple changes such as the type of oil consumed. The relevance of these processes in regards to obesity and its metabolic disorders is particularly stressed