Sweet fiends were born that way: A craving for sweets leads infants to important, high-energy foods. Perception of sweetness has been directly linked to a specific DNA fragment in taste receptor cells, which are found in the intestines as well as the tongue. Mice that were genetically engineered to have "human" taste buds, for instance, showed a human weakness for sweets.
However, people with a high sugar threshold may actually have a low sensitivity to sweetness. These "nontasters" may have only one-third as many taste buds as "supertasters," meaning they need more sugar in foods to get the same satisfaction.