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Matthew McConaughey's taking his upcoming role in The Dallas Buyer's Club super seriously ... the actor has to drop 30 pounds for the upcoming role of real-life AIDS victim Ron Woodroof. The actor showed off his slender frame as he waiting for a cab Friday in NYC.

The movie tells of a heterosexual Texas electrician who was diagnosed with AIDS in 1986; doctors gave him just a few months to live but he refused to accept their prognosis. Instead, Woodroof started an underground alternative treatment operation through which he smuggled illegal medicine to as many AIDS patients as he could. He ended up living six more years and prolonged the lives of countless others.

Whew! Pretty heavy, but pretty awesome -- can't wait to see this film!

Meanwhile, Matthew, 42, has got a third baby on the way and while wife Camila Alves gains weight in her baby bump, MM's got to avert his eyes while she's eating. He told reporters of his weight loss plan: "I am drinking a lot of tea. It takes a while for your body to understand that it has to feed off of itself and that you’re not going to give it something else from the outside."