Is there something special about sugar compared to other carbs? If I had to choose between eating bread or cake for the same calories will cake hurt me more?
The difference is that table sugar and high fructose corn syrup are about 50% fructose (the rest glucose).
While glucose (which is what bread is mostly metabolized into) can be used by every cell in the body, fructose must be broken down by the liver using a metabolic pathway similar to that used by alcohol.
There is a hypothesis that once a person's metabolism has been damaged by enough fructose, that any carbohydrate is likely to cause obesity. Basically, that insulin resistance seems to affect fat cell last and once it sets it glucose will be preferentially absorbed by fat cells.
So people with a well-functioning insulin response should be able to eat relatively large amounts of (non-fructose-containing) carbohydrates without issue, but those in whom the insulin response is damaged (probably a majority of Americans over age 25) might need to cut back on all carbohydrates to stay lean.
But again, this is very much an untested hypothesis.
If the bread is a typical "pedestrian" loaf, there's probably little difference. There is a bigger difference if it's something like Ezekial sprouted grain bread.
