After friends forsake 400 pound teen, he makes radical decision that changed his life

(CNN) -- Throughout high school, Tevante Clark felt ashamed about being overweight.

It wasn't just his hefty size that depressed him, but the distance he felt growing between him and some of his closest friends. Over four years, he watched as his friends steadily left him out of conversations, gave him the cold shoulder at school, and then started excluding him altogether from their Friday night outings around Chapel Hill, North Carolina. He was crushed, spending many evenings alone, feeling rejected.

Standing at 5 feet 7 inches, Clark hit his peak weight at 405 pounds when he was 19.

"I would go home and ask my mom why this was happening to me, but I knew it was because of my weight," he said. "When I would go out with my mom to pick up groceries or shopping, I would wait in the car because I was so embarrassed."

When he started Vance-Granville Community College, he continued to struggle with those feelings.

"I was having suicidal thoughts because of my weight. I even wrote a letter about it that my mom found, and she broke down crying," he said.

"I was tired of everything, tired of people laughing at me, tired of being overweight, tired of being treated differently," he said. "I thought about committing suicide, but I didn't want to leave my mother by herself."

After discovering the letter in his bedroom, his mom said she knew something had to change.

"I saw how depressed he was getting, and that's what hurt me the most," said his mother, Beverly Clark.

But she was not going to let him struggle on his own. She had recently lost more than 100 pounds after a scare from her cardiologist who said she was on the verge of having a heart attack because of her weight. That experience made her believe her son could lose the weight, too.

"He was a junk-aholic, as I was. He had a sweet tooth. He was a snacker -- cakes, cookies, soda, chips," she said.

She was convinced that all her son needed was some guidance about moderation. But Tevante Clark just wanted the weight off. He came to her after many tearful nights and asked if he could get gastric bypass surgery.

Clark was desperate. "I needed a change," he said.

As an employee at Duke University's call center, his mother knew about the school's wellness program Live for Life, which offers a 12-month weight-loss program for employees and their family members. She wanted her son to lose weight, but she also wanted him to try natural methods before committing to surgery. So she made him a proposition: Enroll in the program and try to lose weight naturally for the first few months. If that method failed, they would consider surgery.

When he started in the program in July 2011, his goal was to lose 40 pounds to qualify for gastric bypass surgery. At the start of the program, he was paired with a coach and a dietitian.

Sally Neve, a registered nurse and dietitian, helped him devise a plan to meet his weight-loss goals, which included cutting back on sweetened beverages, eating more fruits and vegetables, and being mindful of portion sizes. He regimented his diet, eating three meals a day and two healthy snacks in between his meals.

Neve also encouraged Clark to get a gym membership. Clark had never worked out. He had played a few pickup games of basketball in middle school, but it was never strenuous. He was nervous and excited for the new experience, but a part of him was sure it wasn't going to work.

He held on to the hope that if he lost just a few pounds, it would be enough to convince his mom that he could do the gastric bypass surgery.

As Clark started working out on the elliptical machine, walking on the treadmill and eating smaller portions, he saw big changes quickly. In the first week, he lost seven pounds. After a few weeks, he started walking 45 to 50 minutes every day on the treadmill with the incline set to high, at a speed that was almost a jog.

After three months, he had dropped 40 pounds, and the urge to have surgery also dissipated. He was now spending two hours a day at the gym.

"He became a changed person," Neve said. "He became confident. He was like, 'I can do this.' I think that is so important for people, to have that confidence that they can succeed."

The salty and sweet snacks were traded in for healthy meals such as grilled chicken and brown rice for lunch and mostly grilled vegetables for dinner. Clark re-evaluated the way he approached food, choosing items such as whole grains and lean proteins to sustain his workouts, not high-calorie sweets to satisfy his cravings.

"He just had to go to someone who could say, 'You can eat what you want, but in moderation,' " his mother said.

After completing the program in December 2012, Clark was down to 280 pounds -- a loss of 125 pounds. But he wanted to be leaner. He started lifting weights on his own. Whenever he came across a piece of gym equipment he was unsure about, he asked a gym staff member to show him how to use it. He discovered he liked lifting weights.

"I liked the leg press. I never tried it, and I learned it works out your hamstrings and quads. When I starting incorporating it into my workouts, I saw improvements in my thighs," he said. The added resistance helped him drop another 100 pounds within a year. In two years, he had managed to bring his weight down to 180 pounds, exceeding all his weight-loss expectations.

Now, happy with his weight, he continues to work out every day. He focuses on building muscle, not losing weight. He does cardio for 15 to 20 minutes and then puts energy toward sculpting his muscles by lifting weights and changing his fitness routine.

The 23-year-old even has a job that requires him to be fit. He works at a UPS warehouse and is on his feet lifting heavy boxes several hours a day.

"If I didn't lose weight, I wouldn't be able to do this job," he said. "There are people who work with me who look like they are fit, but they can't lift like I can. It really makes me want to keep staying in shape."

And his social life? It took a dramatic turn for the better. He has new friends, and a few old ones who stuck by him while he was struggling with his weight. They get together weekly as a group and hang out. Sometimes, he even runs into old classmates who shunned him when he was overweight.

"Now they (say) they are proud of me for losing weight, and that I am an inspiration," he said.

After losing 225 pounds, he said the biggest lesson he learned was not to lose sight of who he was under all that weight.

"Your life will change, but you don't have to change," he said. "You can look at things differently, but don't change who you are just because you changed physically. ... Remember who was there for you and who stayed with you."