Sugar: Sucrose, Fructose, and Glucose

I should be working on my thesis right now, but I got distracted and had to answer a burning sucrose/fructose/glucose question. Namely, what exactly are they? Apparently, sucrose is just regular "table sugar", which is a compound made up of 50% fructose and 50% glucose. Certain fruits (such as pears and apples) have a lot of free fructose (that is, fructose not bound to glucose to form sucrose), and others (sugar cane and beets) have almost no free fructose or glucose. So sugar cane juice is basically just sucrose and water. When this is digested, it becomes equal parts fructose and glucose.

Now, high-fructose corn syrup (HFCS) is usually something like 55% fructose and 45% glucose. This is a bit odd in that there's no sucrose (a disaccharide) for your body to digest, just the component sugars (monosaccharides). Ignoring the whole issue of HFCS containing mercury and being less like naturally occurring sugar than sucrose, the big health issue seems to be a bit more fructose than normal. Fructose is generally considered healthier than glucose because it has a lower glycemic index, but it can actually be dangerous.

Some people aren't good at processing fructose, which can lead to flatulence among other problems, but aside from that, glucose can be processed anywhere in the body, but fructose has to be processed in the liver. When you consume free fructose, the liver stops everything else and gives priority to metabolizing it. When testing was done with rats, their livers looked like those of alcoholics. Also, fructose inhibits two chemicals that reduce your appetite and encourages another that increases it, so yes, fructose will make you fat.

One point I'm not sure about is if the fructose present in sucrose taxes your liver the same as free fructose or not. I think the big issue is that once consumed, free fructose hits your liver all at once, and fructose coming from sucrose enters your bloodstream more gradually. So that's the main rationale for avoiding HFCS in favor of sucrose (i.e., "sugar"). Surprisingly, "crystalline fructose" may be even worse for you than HFCS!