One of the most common diseases in the world is diabetes mellitus. The term diabetes includes a very heterogeneous group of disorders related to carbohydrate metabolism, but these significantly interfere with other metabolic pathways, especially fat metabolism. The key parameter evaluated in diabetes is the level of glucose in the blood (glycemia). Type 2 diabetes, prevalent in the younger population, dominates in the forefront of chronic diseases. It is associated with obesity and poor lifestyle in general. Because diet and nutrients are key components in the regulation of glucose metabolism, in our work we describe important carbohydrates in the diet, their digestion, resorption and basic metabolic pathways of glucose with regulatory sites at the level of insulin and glucagon. We summarize the basic characteristics of the most common types of diabetes, the role of oxidative stress in disorders of glucose metabolism and the possible positive effects of antioxidants.