I don't wish to sound argumentative here, but the correct answer is we do not need carbohydrates, what our body needs is glucose. What we need is some essential amino acids and some essential fatty acids, since our body can not manufacture these from within, hence we need these from an external source, making these certain amino acids and fatty acids essential for life.
Having said that, there are no essential carbohydrates/sugars that our body needs, as it can make glucose from proteins and fatty acids as I've stated before.