The term glycotoxins includes the group of advanced glycation end-products (AGEs) and their precursors, most of them highly reactive intermediary compounds, such as methylglyoxal (MG). Glycotoxins were initially thought to participate in the development of diabetic complications because of their increased formation from glucose. However, they also form and accumulate in tissues since the early stages of disease, such as metabolically unhealthy obesity and prediabetes. Such accumulation has been suggested to result from dysregulated activity of detoxification systems, such as the glyoxalase system, as well as increased dietary consumption, namely from high-glucose and high-fructose foods processed at high temperatures. Although some studies may have used supraphysiological doses, in vitro systems and animal models have shown glycotoxin-induced insulin resistance. Moreover, dietary glycotoxin restriction was shown to improve insulin resistance in humans and glyoxalase (GLO)-1 upregulation improved insulin sensitivity and metabolic function. This review summarizes the current knowledge about glycotoxin involvement in the development of insulin resistance, the mechanisms involved and the usefulness of GLO-1 modulation, and a possible therapeutic strategy to improve insulin sensitivity.