Lifting a cast-iron weight called a kettlebell during a workout demonstration, 24-year-old Kelsey Rentchler appears strong, confident and impervious.

Her looks belie a past of self-loathing.

Rentchler was always the biggest child in her class. She remembers spending recess watching kids run from her, yelling that they were scared she would sit on them.

She would find places in the schoolyard where she could be by herself, or give presents to other kids so they'd be her friends.

Desperate to fit in, she took laxatives and drugs as a teen. She thought about taking her own life.

"Kids can be really mean. Kids' parents can be mean," Rentchler says. "But it was more that they just wouldn't talk to me. I was the fat kid, and I was a very sad kid."

By the time she was 9 years old, she weighed 140 pounds, had breasts and was menstruating. In middle school she surpassed 200 pounds. At age 21, she weighed 312.

The excess weight took a toll on her 5-foot-5-inch body. The emotional damage was just as severe, says Rentchler, who now teaches first aid and computer applications at Apollo College.

About 80 percent of people who are overweight experience depression, and that includes children, the National Alliance on Mental Illness of Southern Arizona says.

Rentchler's parents divorced when she was 12, and she often got meals for herself. She remembers summers of doing little except for eating - bologna, white bread, ice cream, Hamburger Helper, fast food.

She took only one semester of physical education in her freshman year of high school. A walk across the street left her panting.

"I was definitely depressed," Rentchler says.

On March 17, 2007, at age 22, she had lap-band weight-loss surgery, in which a surgeon uses an adjustable, inflatable band to shrink the stomach.

Within six months she lost nearly 60 pounds.

Then her friend, personal trainer Danny Sawaya, convinced her that being fit and active was more important for her overall health than being thin.

It wasn't easy for Rentchler.

The thought of going to a gym and working out in front of others frightened her. And getting over that anxiety was scary.

"It's like jumping off a diving board for the first time," says Sawaya, the general manager of SWAT Fitness in Tucson.

Sawaya says Rentchler was like two people - extroverted and confident in her work life, but negative and defensive when it came to personal matters.

He knew she was capable of confidence in all areas of her life, so he stood by as she worked out - in a busy gym. Her body became stronger and Sawaya says Rentchler became more positive.

She's lost more than half her body weight and feels much happier. But Rentchler still struggles with remnants of her old self.

"When you have a bad body image," she says, "you just pick yourself apart."