Chris Rennick decided to lose weight after his doctor informed him that he was obese

Credit: Courtesy Chris Rennick; Nutrisystem/Ken Lee

After doing two tours in Iraq as a Marine, Chris Rennick returned home and found himself piling on weight.

“In the Marine Corps, you’re burning 10,000 calories a day running around with gear on, combat stress, things like that. It takes a toll on your body but it keeps you in shape,” Rennick, 34, tells PEOPLE.

“When I came out, I was overeating, dealing with PTSD,” he continues. “It was a combination of stress from transitioning, trying to find a job, and leaving my brothers that I was lifelong loyal to, and not being on a set schedule [that caused the weight gain].”

Before he knew it, Rennick had gone from 185 lbs. to 289 lbs.

“It was something I was ashamed of,” he says. “I didn’t want to take to pictures. I didn’t want guys I was in the Marine Corps with to know that I was so overweight.”

His weight started to interfere with his job as the veteran district representative for a Congressman, which required him to speak at events.

“An unsettling feeling was having to speak in public, and being out of breath after every couple of words; having to walk up the podium steps, and being out of breath by the time I got there going up five or six steps,” says Rennick. “Halfway through my speech, which would be four to five minutes, I would already be sweating.”

But it wasn’t until an alarming visit to his doctor that he realized he really needed to make a change.

“The most extreme moment was when I was speaking with my doctor in 2013, and she told me, ‘You’ve got high blood pressure, you’ve got high cholesterol, and you weigh 289 lbs.’ She said, ‘You are obese,’ ” he recalls. “It was something I took very seriously. When she used the term ‘obese,’ it was something that triggered me.”

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Rennick first tried extreme dieting, eating mostly salads and chicken, while trying to maintain a vigorous workout schedule.

“I guess it was my mentality from being in the military – I wanted to push myself to the extreme,” he says. But he found living that way was not sustainable. “I got these mild to extreme crashes.”

After trying several other diets to no avail, Rennick decided to try Nutrisystem. At first, he was eating the meals for lunch, then breakfast and lunch, and by January 2014 he was on the plan full-time.

“I did the research and saw that I could actually eat this and my cholesterol was getting better, my blood pressure was getting better,” he says. “It was keeping my energy levels consistent, and I wasn’t overeating.”

By the end of February 2015, he had lost 120 lbs.

“I’m a lighter weight than I was when I was in the Marine Corps,” says Rennick. “I’m also doing more pull-ups now than I did when I was in the Marine Corps. I thought I was in such good shape three years ago! To have abs better than I ever did when I was in the Marine Corps is something to be proud of.”

Now Rennick goes on daily morning hikes, and finds that he still has tons of energy after – which he needs as a father of three.

“When my children want to play, not only do I have the energy to do my workout, I can also play with them for the rest of the day,” he says. “And having three children takes a lot of energy!”