Mannitol is a polyol made by hydrogenation of fructose. It was first isolated from the sap of a flowering ash tree found in southern Europe and Asia.
Mannitol is about half as sweet as sucrose. It has a cooling effect in the mouth.
Mannitol is not efficiently absorbed by the body, and it is only partly metabolized. Its caloric value depends on several factors, as discussed in my essay "Polyols and Calories." In the USA, lactitol provides 1.6 calories per gram for labeling purposes. In the European Union, it is listed at 2.4 calories per gram.
Unlike sorbitol, mannitol does not bind water well. It is used as a dusting powder on chewing gums. It has a high heat stability and can be used in chocolate ﬂavored coatings.
Mannitol occurs naturally in mushrooms, algae, and trees. The FDA permits use of mannitol in the USA. The Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives (JECFA) has concluded that mannitol is safe. The Joint FAO/WHO Expert Committee on Food Additives has determined the "Laxative Threshold Value" (LTV) for a number of polyols. It estimates the LTV for mannitol to be between 10 and 20 grams per meal. The FDA requires the following label statement for foods whose reasonably foreseeable consumption may result in the daily ingestion of 20 grams of mannitol: "Excess consumption may have a laxative effect."
Mannitol is used medically as an osmotic diuretic, but it has to be injected intravenously to be effective. Mannitol is not well absorbed from the digestive system, so mannitol in foods will not have a diuretic effect.