There is growing evidence that consumption of added sugars play a role in the recent increase of metabolic diseases: 1) The intake of derived caloric sweeteners has increased in conjunction with rising prevalence of obesity; 2) Epidemiologic data and experimental studies show a positive correlation between sugar, fructose or sweetened beverages consumption and component of the metabolic syndrome. Several questions regarding effect of natural sugars on health are not answered yet, particularly the interactions between sugar intake and environment factors including ethnicity background and physical activity. Only Interventional studies will elucidate if there is a causal relation between sugar intake and metabolic diseases in humans.