<p>You've seen Queen Latifah and even Jason Alexander strut their stuff to show off their slimmed-down physiques for Jenny Craig's prepackaged meals and diet programs. Now, in an ad for Weight Watchers, Jessica Simpson is doing it too. In the ad she says, "I'm not a supermodel. I'm just Jessica trying to eat real food in the real world" -- with a big fat profit motive from being a spokesperson. Americans spent more than $1.1 billion in 2011 on such programs, as well as meal-replacement shakes and bars, according to Marketdata Enterprises. Marketdata says many people stay on the plan for 12 weeks. At that point, they've either reached their goal or quit. Many stay on for years.
$1,251: 12-week program (includes $75 membership fee, $98 per week for food) -- Jenny Craig
$129: 12 weeks of passes and access to online tools -- Weight Watchers
$689-$950: 12-week program (includes all meals and dessert) -- Nutrisystem</p>