Tiny Tim was rescued just before Christmas 2011 and taken to Southside Place Animal Hospital in Houston, ABC News reported.
He was looked over by veterinarians and proved to be otherwise healthy -- save his weight, which was a hefty 35.2 pounds.
"Because he was so huge, he had trouble walking. He had trouble standing," hospital manager Debbie Green said.
After a failed attempt at finding his owners, Tiny Tim received permanent residency at the hospital where doctors put him on a special diet that provides him with 307 calories a day.
"He has been on a very, very regimented diet -- measured meal plans, the whole works and he is at 28.6 pounds," Green said. "He weighs in twice a week, and he gets meals measured in little bags throughout the whole week, so we know exactly what he's eating."
Tiny Tim, who is about 9 years old, also gets regular exercise, said Green, who added the goal is to get him closer to 20 pounds.
"He did better than most people. I think he could be on the 'Biggest Loser' show," Green joked. "It's been slow and steady but very good for him."