Santa has been slimmer in the past, specifically, as St. Nicolas, before literature from the 19th century began to note a more "jolly" side to Santa. By the early 20th century, a Coca-Cola campaign illustrated him at his heavier weight (perhaps from drinking too much soda from the 1930s onward). Efforts to lose weight were demanded from Santa's employer, Walmart, which required him to lose weight or face increased insurance premiums. (You're not really surprised he was working for the retail giant, were you?)
Santa underwent the transformation using advice from his internist, but was so confident he could lose weight, he actually put money on the effort. He turned to a company that gambles on whether subject can lose a set amount of weight in a given amount of time. The company places bets on how much weight people can lose. (It profits because only one in four people collect.)
