It's not as simple as that. You could eat a whole tree, about 80% carbs, and it won't affect your BG levels at all. Humans don't produce the cellulase enzymes required to break cellulose down.
On a grass plant, most of the structure is cellulose. Even the grass seeds, rye, wheat, barley etc contain lots of cellulose and it simply passes through the human digestive system. The carbs in beans, lentils etc also contain carbs which contain oligosaccharides which are only partially broken down by enzymes. Mostly, these carbs enter the lower intestine undigested and are broken down by bacteria, hence the wind, but these carbs are also mostly, not turned into simple sugars.