Glucose or 'Blood Sugar': is found in most starches and is released by the breakdown of those starches in the mouth (by salivary amylase) and in the gut (by pancreatic amylase). Interesting, pure glucose is not common in the American diet. Sources of pure glucose include 'old fashioned' corn syrup (think Karo) and 'dextrose' (the common name for glucose). The main reason glucose is not more commonly found in American foods is that it is not very sweet compared to other sugars.
o Also called "Blood Sugar", glucose is the "Sugar of Life". Unfortunately, it can also be the sugar of "death" when excessive levels of this sugar accumulate in the blood.
o "Glycemic Index" is determined by studying how fast certain foods cause blood glucose levels to rise.
o Glucose is rarely found as a pure sugar in nature. It is found in some fruits, but usually along with other sugars like fructose and sucrose.
o All starch (potato, wheat, rice…ALL of it) is composed of nothing except glucose, but in starch, the glucose is not "free". Instead, starch is VERY long chains of glucose molecules all chemically bound together. However, digestion of starch always produces only one simple sugar: glucose. This is why starches are so important to glycemic index.
o Wood and bran are also made of long chains of glucose called "cellulose", but the chains cannot be broken by humans or even by the bacteria in our gut. Therefore cellulose has zero nutritional calories and is more commonly called insoluble fiber or "roughage". Just FYI, cellulose certainly DOES have "chemical calories" as evidenced by the fact that wood gives off a lot of heat when it burns (remember that calories are just energy or heat).
o Old-fashioned Karo corn-syrup is mostly pure glucose.