The gut doesn't absorb sugar as well in the presence of fibre so I think people tend to subtract the amount of fibre from the total carbs to come up with someth

The gut doesn't absorb sugar as well in the presence of fibre so I think people tend to subtract the amount of fibre from the total carbs to come up with something called net-carbs. No idea how well this works in practice of course but there is definitely some high percentage of sugar not absorbed for every gram of fibre added.