Standing on the National Mall on a frigid afternoon, Caress Weems, 28, confides, "I would love to be Beyoncé-size." The government worker, who says she is 30 lbs. from her goal, also has diabetes in her family, which she wants to avoid. But motivating herself "hasn't been working. So I thought, 'Why not do the Challenge?'"

That's just what Celebrity Fit Club diet expert Dr. Ian Smith hoped to hear. On April 7 Weems and more than 5,000 others joined Smith, 37, on the Mall to kick off the 50 Million Pound Challenge. (Similar events in 13 other cities are scheduled.) In the two-year initiative, Smith wants 5 million African-Americans to lose at least 10 lbs. each. That may not seem like much, but, he says, the program isn't just about the scale. Citing high rates of obesity in the black population (45 vs. 32 percent of all Americans), Smith says, "This is about taking a better look at overall health."

"It's a support system," says Fit Club veteran Kimberley Locke, who performed, along with Patti LaBelle, at the event. "On Fit Club we had each other. Here, people form a pact and become obligated to each other to do this." So far, almost 16,000 have committed to the State Farm Insurance-sponsored program on a Web site (www.50millionpounds.com) that provides exercise and diet tips and tracks participants' cumulative weight loss: 4,953 lbs. to date. Says the TV doc best known for his no-nonsense "Fat Smash" diet: "I would love for this to be my legacy."