On the Brooklyn set of their FX firefighter drama Rescue Me, Denis Leary glares accusingly at costar Lenny Clarke.

“There’s a tiramisu in the makeup trailer,” teases Leary. “I had nothing to do with it!” protests Clarke. “Well, I’m having a big chunk,” says Leary. “Only to help you with your diet.”

Add to Leary’s resume the unlikely role of personal diet coach. With his encouragement-playful threats, really — Clarke has lost 144 lbs. Following cancelled TV series in the ’90s and a divorce, the 6′2″ actor went from 176 lbs. to 380.

“I was out of my mind eating,” says Clarke, 53, who developed high blood pressure and difficulty breathing. “Denis was like, ‘You’re gonna die.’”

But Leary — Clarke’s friend of 28 years — had a plan. As a writer and producer of Rescue Me, Leary asked, “If you had to do it for the show, how much weight could you lose?’” Clarke recalls. “I said, ‘100 lbs.’”

Then, with a plot line that sent Clarke’s character to prison (where he would waste away doing time), season 3 and 4 viewers watched him shrink. “The ‘Murder 1 Diet,” jokes Leary.

In reality, Clarke joined Weight Watchers, began biking and swimming daily and eating salads, fruit and fresh fish, the last provided by wife Jennifer, a fishing boat captain.

Though Clarke would like to lose another 36 lbs. to hit 200, Leary is already very proud. “I can’t believe there’s not a special weight-loss Emmy,” he says. “Why doesn’t Oprah have awards for that?” [via]