In particular, raising blood sugar will increase the production of what are known technically as reactive oxygen species and advanced glycation end-products, both of which are potentially toxic. The former are generated primarily by the burning of glucose (blood sugar) for fuel in the cells, in a process that attaches electrons to oxygen atoms, transforming the oxygen from a relatively inert molecule into one that is avid to react chemically with other molecules. This is not an ideal situation biologically. One form of reactive oxygen species is those known commonly as free radicals, and all of them together are known as oxidants, because what they do is oxidize other molecules (the same chemical reaction that causes iron to rust, and equally deleterious). The object of oxidation slowly deteriorates. Biologists refer to this deterioration as oxidative stress. Antioxidants neutralize reactive oxygen species, which is why antioxidants have become a popular buzzword in nutrition discussions.

The potential of advanced glycation end-products (AGEs) for damage is equally worrisome. Their formation can take years, but the process (glycation) begins simply, with the attachment of a sugar—glucose, for instance—to a protein without the benefit of an enzyme to orchestrate the reaction. That absence is critical. The role of enzymes in living organisms is to control chemical reactions to ensure that they “conform to a tightly regulated metabolic program,” as the Harvard biochemist Frank Bunn explains. When enzymes affix sugars to proteins, they do so at particular sites on the proteins, for very particular reasons. Without an enzyme overseeing the process, the sugar sticks to the protein haphazardly and sets the stage for yet more unintended and unregulated chemical reactions.

The term glycation refers only to this initial step, a sugar molecule attaching to a protein, and this part of the process is reversible—if blood-sugar levels are low enough, the sugar and protein will disengage, and no damage will be done. If blood sugar is elevated, however, then the process of forming an advanced glycation end-product will move forward. The protein and its accompanying glycated sugars will undergo a series of reactions and rearrangements until the process culminates in the convoluted form of an advanced glycation end-product. These AGEs will then bind easily to other AGEs and to still more proteins through a process known as cross-linking—the sugars hooked to one protein will bridge to another protein and lock them together. Now proteins that should ideally have nothing to do with each other will be inexorably joined.