Mannose is a “six-carbon-sugar,” as are the better known and closely related substances glucose and fructose. Relying on evidence that is both exceedingly preliminary and highly inconsistent, some alternative medicine practitioners have popularized mannose as a treatment for urinary tract infections.

Mannose plays an important role in human physiology. However, there is no nutritional need for this substance, as the body can easily produce it from glucose. Nonetheless, significant quantities of it can be found in many fruits and vegetables, including peaches, apples, blueberries, green beans, cabbage, and tomatoes.