Thanks for this response. As you said, glucose and fructose are isomers of each other, and this is why the branching of the sugar molecule is so significant, but I can’t find any information about additional isomers. I think all fructose is chemically the same, regardless of its source, but I’m open to being corrected if someone has a source. If the claim is true, it’s surprisingly hard to verify, which makes me suspicious.
Your study is worth looking at, but I think there are caveats too. First, rats may just be more sensitive to fructose than humans, which would make sense since fruit wouldn’t have been as important a part of their ancestral diet. I don’t think controlled human studies have found the same problems with fructose and weight gain. Second, in the first part of the study, the abstract notes that “Rats with 12-h access to HFCS gained significantly more body weight than animals given equal access to 10% sucrose, even though they consumed the same number of total calories, but fewer calories from HFCS than sucrose.” For some reason, they gave the rats an 8% solution of HFCS, but 10% of sucrose, and the rats that gained weight ate fewer calories from the sweetened solution (and more of some other unnamed food source). It seems the controls were a little off balance.
That said, I don’t want to dismiss the study, and I think many people have shared your experience of gaining weight while eating fructose. On the other hand, I’ve met plenty of skinny sugar freaks too. My own feeling is that it can be easier to over-consume calories when we eat a lot of sugar, but the sugar itself may not be the problem. It’s the overeating and/or lack of exercise.
There has also been research done on the athletic benefits of fructose, and it does seem to more rapidly facilitate glycogen recovery. For athletes who burn a lot of calories (or just everyday gym rats) a post work-out glucose/fructose drink (i.e., a soda) could actually be nutritionally superior to pure glucose. That said, it doesn’t make sense for sedentary people to eat like they’re athletes!