Insulin resistance is associated with type 2 diabetes, hypertension and cardiovascular disease and the dietary factors involved in these metabolic disorders are still misunderstood. In animal studies, sugars, particularly sucrose and fructose, have been shown to decrease insulin sensitivity, with potential association with an induced hypertriglyceridemia. But in humans, the effects of sugars on insulin sensitivity are still debated. The present work first gives an overview of the metabolic pathways that could be implicated in the development of insulin resistance by sugars. Then, a review of the studies (intervention, prospective and cross-sectional) on the relationship between sugars, insulin resistance and diabetes is made in order to determine the level of proof concerning the association of sugars consumption and diabetes. All these studies failed to demonstrate an obvious relationship between the intake of total simple carbohydrates and glycaemic control or risk to develop a type 2 diabetes and particularly specific evidence is missing in terms of sucrose effect on diabetes. Concerning fructose, there are still discrepancies between studies' conclusions about the long-term deleterious effect on diabetes development. But its effect on lipogenesis and triglyceridemia has to be taken into account, considering the growing use of fructose in food industry and sugar-sweetened drinks.