Good Eats Arrowroot Flour/Starch is obtained from the tuber of the arrowroot plant which is then ground into a fine powder. It can be used in many baked goods, and can be used to thicken soups or sauces. Using arrowroot flour/starch is an excellent way to reduce carbohydrates in baking as well as replace gluten in your diet. Arrowroot flour/starch is a good source of fibre and calcium.