It is confusing. The term sugar for most people means it will be sweet. Starch is not sweet. Biochemically, those 5 and 6 carbon rings are sugars, but this is not what we call sugar on our tables. Table sugar is sucrose, and sucrose is a dimer of fructose and glucose, which chemically are simple sugars. HFCS is also fructose and glucose. Starch does not equal sugar. When it is digested, it equals glucose. Starch is in fact as you say a polymer, but a polymer of glucose, so no fructose molecule is present. Fructose metabolism is very different from glucose metabolism, and it appears that fructose might be a culprit in obesity, metabolic syndrome, and type 2 diabetes. Starch is a carbohydrate, as is sucrose. Sucrose is also table sugar.
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