The reaction in which reducing sugars and amino acids in food are nonenzymatically condensed is distinguished from glycosylation, which is the enzymatic addition of sugar chains, and is called glycation. This reaction is derived from the discoverer and is called the Maillard reaction, which is also called glycation; however, in the later stages, advanced glycation end products (AGEs) are produced [1] (Fig. 54.1). Hemoglobin A1c is one of the early products of this reaction, an Amadori rearrangement product, and is already used worldwide as an indicator of blood sugar control. However, AGEs are produced from various pathways, and because their measurement methods differ, there are still challenges in quantifying endogenous AGEs. To date, the content of endogenous AGEs has been evaluated by fluorescence intensity; however, in recent years, with the advancement of mass spectrometry, the quantification technology of identified AGEs in the body has progressed, and the connection with age-related diseases has become clear [2].