> People enzymatically convert corn sugar to match what comes out of sugar cane. Straight-up corn sugar is harmless, "high-fructose" is deadly.

Corn sugar is the monosaccharide glucose (more specifically its a specific stereoisomer of glucose called dextrose or D-glucose).[1] Cane sugar is sucrose, which is a disaccharide of composed of glucose and fructose.[2]

There is no way to enzymatically convert a monosaccharide to a disaccharide, you would need to be joining the glucose together with a fructose, which, as we are not fruit don't just have naturally occurring in our body.

When you eat sucrose, the enzyme sucrase-isomaltase located in the small intestine catalyzes its hydrolysis into fructose and glucose.[3,4] High-fructose corn syrup is a mixture of glucose and fructose which is exactly what you get when your body enzymatically breaks down sucrose.[5]

So corn sugar is glucose. Sugar can is sucrose. And high-fructose corn syrup is a mixture of "pre-digested" sucrose. I think that high-fructose corn syrup is probably bad in that its in everything and cheap, but I can't see how its any worse than regular sugar. And corn sugar is not the same as regular sugar, it lacks fructose entirely.

[1] https://en.wikipedia.org/wiki/Corn_sugar

[2] https://en.wikipedia.org/wiki/Sugarcane

[3] https://en.wikipedia.org/wiki/Sucrase

[4] https://en.wikipedia.org/wiki/Sucrase-isomaltase

[5] https://en.wikipedia.org/wiki/High-fructose_corn_syrup