Tony Mims always smiled, but he'd had a tough life. The son of alcoholic parents, he left home when he was 14 and worked in the fast-food industry.

Over time, Mims' weight ballooned.

"I'm tired of having limitations of what I have to do," he said. "And I sweat like crazy. I'd give one of my kidneys to have a smaller body."

Mims was tasting wedding cakes with his fiancée when Chris Powell, the trainer on "Extreme Makeover: Weight Loss Edition," showed up and pledged to help him change his body and his life.

At the weigh-in, Mims, then 49 years old, got harsh news. After years and years of overeating, he weighed 398 pounds. He had to be weighed on a truck scale.

As part of Mims' weight-loss program, he would learn how to cook healthy meals. Powell got him exercising.

It wasn't easy. Added to the pressure, Mims' son, Marcus, fell ill. His son suffered from cerebral palsy, and the hospitalization helped put things into perspective for Mims.

"I'm here fighting for my life and he's in the hospital fighting for his …," Mims said tearfully.

Powell moved in with Mims and his fiancée, and helped them remake their home. For a while, things went well, at 90 days into his program, Mims weighed 294 pounds.

B ut Mims and his fiancee were having trouble. The relationship fell apart, and he moved out of the home he shared with her.

When it was time for Mims' six-month weigh-in, Powell couldn't find him. That's because Mims was living in his car. He had become homeless.

Then, Mims got devastating news. His son had died. Rather than derailing Mims, the news strengthened his commitment to the weight-loss program.

When he showed up for his nine-month weigh in, the results were amazing. He weighed 226 pounds, for a total weight loss of 172 pounds so far.

He was now ready to have the excess flesh on his frame surgically removed.

Three months after the surgery, his friends and family gathered for his 50 th birthday, and he had a final weigh-in. He weighed 200 pounds.

Mims found a new love, and is engaged to be married.

The episode of "Extreme Makeover" that chronicled Mims' weight-loss journey aired Sunday on ABC.