Drew Manning:Personal Trainer Packs on Pounds to Experience Overweight Life

"I have always been the fit guy," Manning told "Good Morning America." "So to better understand what my clients go through, I decided to let myself go for six months, no exercise and unrestricted diet."

Today, 25 weeks later, his waist has nearly doubled to 47.5 inches, his neck has grown by 2 inches and he has gained 76 pounds, up to a hefty 269.

Manning, a married father of two young children, saw his body change, his glucose level skyrocket and his blood pressure rise to a level he called, "off the charts."

Through weekly weigh-ins, photos, blogs and videos, followers have been able to see not just Manning's physical transformation, but also the mental changes he says even he wasn't prepared for.

"I figured I'd just get fat and then I'd get back to thin, that it'd be that easy," Manning said. "There were a lot of emotional and mental changes which I didn't factor in when I first started this journey."

"What hasn't changed," his wife, Lynn, asked on "GMA." "He's tired. He's sore. He complains all the time. It's hard for him to help out and do the everyday things that were so easy for him."

Her husband concurred. "I feel like I want to cover up, even in front of her," he said of his hesitancy now to show the body on which he built a career.

"It's affected me as a dad, not being able to play with my 2-year-old girl," he said. "Emotionally, I can only imagine what other people go through not being able to do those things."

Armed now with the empathy for his overweight clients that prompted his weight-gain experiment, Manning is preparing for the second, fitness-focused leg of his journey, a path he is much more confident to face.

For Manning, this reverse transformation, which he plans to achieve through a diet and exercise regime all documented on his website, is what his Fit2Fat2Fit mission has been about.

"The whole purpose of this side of the journey is to invite as many people as possible to join me," he said. "People can follow my exact meal plan and my workouts on my website for free and have full access."

Calling his weight gain "worth the risk," Manning believes he has accomplished the goals he set back in May at the start of his Fit2Fat2Fit program.

"It was worth it to me," he said. "The fact that tens of thousands are following me and are inspired by this; to me, it's worth all the craziness."