We saw "March of the Penguins" and one of the most striking elements of the Emperor Penguin lifestyle has to be the extreme relationship to food: periods of fattening and periods of starvation in an annual cycle which regularly halves and doubles the body weight of both males and females.
Nearly simultaneously, my spouse and I had the same thought: Extreme Adventure Dieting! Perhaps Antarctic conditions would be inappropriate for all but the most truly extreme cases, but if you combine fasting with maternal/paternal caretaking duties, you might be able to convince some people that they're getting in touch with their inner Emperor ("getting in touch with your inner Penguin" won't market as well, trust me) and that will help them lose weight.
Here's the theory: you find a reasonably extreme environment, hot or cold. You give the participants something to care for, preferably something they need to shield with their own bodies for long periods of time. (eggs are good; plants work, too, and you can take them home more easily) Then you monitor their success and sharply limit their food intake. You'd have to include a meditative component (what do the penguins think about for months on end other than "It's Cold" and "Don't Drop It" I wonder? Or is that their limit?), probably drawn from one of the more salvationist traditions (in keeping with the caretaking aspects; people would love to be meditating on the salvation of Kuan Yin while carrying out a mission of mercy: they could empathize with Boddhisatvas and other saviors!) in order to keep people focused on the task and away from the food.
True Extreme Experience afficionados, of course, are already pretty thin sorts. For them part of the extreme experience would have to include fattening up, preferably in a predatory fashion. That's a whole other branch of the business, tied to the "stone age diet" plans....
[Welcome Carnival of the Vanities readers (thanks, Mark, for the suggestion....), Carnival of Comedy readers!]