The Oscar winner, 61, has also "pretty much cut out the drinking" except for special occasions.

In addition, "he's working out with a personal trainer and doing a lot of cardio to burn off the fat."

"He's lost a good 30 pounds at this point, but he's still hoping to drop another 20 pounds to get back to a healthier weight," the source noted.

"It's not really about how he looks, this is about his overall health and making sure he's around for many years to come," the insider pointed out. "But, of course, he wants to look his best when he walks down the aisle and that means getting rid of his belly!"