Fructose is utilized as a fuel source, but in a different pathway than glucose (I'm at home right now and all my textbooks are in my ofice, so I can't reall comment on the efficiency of fructose metabolism). Since sucrose is a composite substance, consisting of one fructose molecule and one glucose molecule, the body has to cleave the sucrose molecule into its two glucose/fructose components before "sucrose" can enter either metabolic pathway.
But you correct in that fructose does not stimulate the same insulin response as sucrose. However, this is probably because the glucose component (which is the stimulant for insulin) is the one that does all the insulin-stimulating work.
Whether products with HFCS in them have lower or higher glycemic indices, I have no idea. I suspect that if fructose and glucose exist as separate entites in HFCS that it would have a higher GI than sucrose since energy would not be required to separate the two in HFCS as it is for sucrose.
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