yacon Polymnia sonchifolia, a plant of the sunflower family which is indigenous to the Andean region of S. America. It is valued for its round or spindle-shaped tubers, which are usually eaten raw, but can also be boiled or baked. They have little nutritional value, but provide a pleasantly sweet and crunchy addition to salads, with a refreshing flavour; they have been compared to apples and watermelons in this respect.
Unlike the majority of roots and tubers, but like other relations of the sunflower, yacon stores carbohydrates mainly in the form of inulin. This consists largely of fructose. Humans have no enzyme for dealing with inulin, so it passes through their digestive tract without being metabolized and, as a consequence, yacon provides few calories and may have some potential as a low-calorie sweet diet food.