I hope you realize that the whole process of yeast fermentation results in sugars being made from the yeast digesting flour carbohydrates. If you want to cut out all sugar from your diet, that litterally is impossible. Added to that, your brain requires a ton of glucose to function during the day; it is a huge consumer. Without any sugar your blood sugar plummets and you faint because there isn't enough energy going to your brain. If you want to cut down on sugar, best to elimate soda, candy, ice cream, and cookies from your diet rather than nit pick over the relative small amount of sugar in a typical fresh sourdough loaf from a bakery.