Story highlights Fitness trainer Drew Manning wanted to better understand his clients' struggles

Manning gained 70 pounds on purpose so that he could lose it

Back at normal weight, he says the psychological aspect to dropping pounds is important

(CNN) When Drew Manning stepped out from behind the cardboard cutout of his former fat self on Monday, the audience of "Good Morning America" was appropriately shocked.

The fitness trainer's journey had come to an end after successfully losing more than 70 pounds -- six months after he purposely gained the same amount. "Like it never happened," host George Stephanopoulos said.

"Kind of," Manning said. Both Manning and his wife, Lynn, can attest that a lot actually has changed in the past year. While Manning's body may have returned to its six-pack heydays, his mind, in many ways, has not.

Always a fitness junkie, staying in shape comes naturally for Manning. He's that guy at the gym the rest of us love to hate, the one who likes to use his biceps for pumping iron instead of changing channels, and who prefers sucking down a spinach shake to indulging in a brownie sundae.

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Because of that, Manning was a "judgmental" trainer, his wife says. "He would look at someone who was overweight and say, 'They must really be lazy.'

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