Sign of the Times: Jason Alexander, Diet Guru

>First Lady Michelle Obama has made it her signature issue. Sesame Street's junk food-loving Cookie Monster sings about it. But perhaps the surest sign obesity concerns have hit the mainstream is that Jason Alexander—otherwise known as Seinfeld's George Costanza, a character who once ate cake out of a trash can—has become a spokesperson for Jenny Craig.

Alexander's campaign for the weight loss company started earlier this year with an ad that highlighted the 15 pounds he lost in five weeks—even though he ate pancakes and French toast along the way. And this week he offers an update on his weight loss—30 pounds in 18 weeks—and a song and dance routine that could be seen as horrifying or hilarious depending on how much you loved Seinfeld and how well you can tolerate Full Monty references:

This ad also marks a significant departure in Alexander's career in commercials, in which he's done spots promoting junk foods ranging from the relatively healthy (Rold Gold pretzels) to the seriously not (processed onion-flavored hamburgers). His first major post-Seinfeld role was as a spokesman for Kentucky Fried Chicken:

And while Seinfeld was still on, he promoted Rold Gold pretzels—and their low fat content:

But some of the Alexander's most memorable junk food ads came before he was famous. Here's one for a Delta Gold potato chips:

And another for Hershey's Kisses:

And one for Lipton Soup—which sounds healthy enough until you realize the mix is being promoted here as a filler for hamburgers:

So what's Alexander going to hawk now that he's slimmed down? Maybe he'll join his former Seinfeld co-star Julia Louis-Dreyfus as a spokesperson for Healthy Choice.