Smith's doctors told the Phoenix native to lose the weight or he would only have about four years to live. Smith felt so unworthy he had thought about ending his life even sooner than that. He believed he deserved to die, and in a very painful way.
"I just decided maybe me dousing myself with gasoline, maybe people could hear my screams and hear all the despair that consumed me for all these years," Smith said.
In those moments of despair something clicked for Smith. Fed up with the fat, he decided to get fit. Smith e-mailed Chris Powell, a local health and fitness expert at "Good Morning Arizona" and would not take no for an answer.
"To have someone say I really want to lose 400 pounds, I was like that's nice but are you really ready to make that commitment?" asked Powell, a personal trainer.
Smith's answer was simple. "I knew that if I didn't, I was going to die," he said.
The Weight Loss Pact
When Powell met the overweight young man for the first time, he was taken aback by his massive girth.
"It was definitely shocking because I didn't know what 600 pounds looked like," Powell said. "When he opened the door it was doorframe to doorframe."
At first Powell wondered what he had gotten himself into, but he also saw something else in the painfully shy Smith.
"He was just so broken," Powell said. "You could see how weak he was. And I don't mean weak as in physically weak, but just that he had no social skills. He really didn't know what to say or what to do. He couldn't even look me in the eye."
The trainer knew he had to do something to help unlock the personality of this young man who had been imprisoned by shame and social anxiety.
"I had a very bad social phobia," Smith said. "I didn't leave the house and I didn't even feel comfortable in my own backyard until it was dark out."
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From Shy to Social
At 630 pounds, Smith never had the kind of life that most young people take for granted. He couldn't play sports, never went to a school dance, never had a date and had never been sexually active. He was always teased and taunted and had no friends.
Powell agreed to help Smith but on the condition that he give the weight loss regimen his all. Smith hit the gym and kept up with a healthy, balanced meal plan devised for him by Powell.
In just four short months Smith was 100 pounds lighter. In 26 months, Smith had lost 401 pounds naturally, without surgery or supplements.
"At first it was like let's aim for 230, that's 400 pounds, but 400 pounds it's just too even," Powell said. "But if you say 401 pounds every pound counts."
He decided to step out on the social scene in hopes of finding that special someone, so Powell orchestrated Smith's first night out on the town.
"I said I need to make this fun for him and I want him to just kind of see how good people really are so I made a couple of phone calls to a few of my buddies that are managers of bars or bartenders and I let them know that we were going to be coming in," Powell said.
Smith was still about 400 pounds and Powell knew it was risky to dump David into the superficial waters of local nightlife, but he was pleasantly surprised.
"He was the man," Powell laughed. "He walked in, the girls are kissing him on the cheek and everyone is high fiving him. When we got in the car and I'm driving him home, he goes, that was the best night of my life."
Eventually, David had to undergo two surgeries to remove 23 pounds of flesh, but that wasn't his only procedure. After having Lasik surgery for his eyes, cheek implants and cosmetic dental work, which also helped boost his confidence.
David Smith and Chris Powell: A Story of Friendship
After two years of working together Powell and Smith became very close, even sharing a bachelor pad. The trainer never charged Smith for his services, and he says that what he got in return was much more valuable -- a best friend.
"I've cried on his shoulder a lot more than he's cried on mine. He's been with me through the worst times in my life," Powell said. "I was with him through his physical transformation and his emotional transformation but he's been with me through my own journey over the last couple of years, and that's the real reason why we're so close."
Smith's dramatic weight loss and their story of friendship have garnered worldwide attention. From television appearances here and abroad, to an online fitness program called Reshape the Nation, the duo are now on a mission to transform the lives of others. Powell even inspired Smith to give back.
"I helped him through his ACE exam and how he's a certified personal trainer," Powell said.
David Gives Back
"David's story was very inspirational to me," says Jeff Flosi a salesperson for Cox Communications in Arizona. "I was about 525 to 550 pounds and he was heavier than I was. And knowing that he worked it off and didn't do any type of gastric bypass or anything like that and did it the hard way, that's kind of what attracted me."
Using the same carb-cycling formula that Powell created for him, Smith has helped Flosi lose 149 pounds in 10 months.
"I've learned from David it's not about the numbers," said Flosi. "The important part at the end is to be healthy and to be active and feel good."
That's the kind of transformation Smith wants people to get from his training and from his story. While he's still on a journey to improve his life, Smith strives to make others aware that they can change their lives too.
"If somebody was in my shoes a few years ago, I would just tell them not to give up, not to lose sight of what they really want in life and go get it. I got it."