What Is Mannitol Powder? Mannitol powder is a sugar alcohol that is commonly uséd as a sugar-substitute sweetener. It is found naturally in a variety of foods, such as strawberries, mushrooms, celery, onions, and pumpkins. Mannitol Powder Benefits* Mannitol powder is most commonly uséd as a sugar-substitute sweetener, but it may have some health benefits when taken as a supplement. Mannitol may support the digestive system, kidneys, and bladder.