How this woman went from 350 pounds to 4-time marathoner

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Liz Rock started her transformation journey four years ago weighing 350 pounds.

The 29-year-old Boston resident is now 150 pounds thinner, a four-time marathoner and a fitness instructor.

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"At 350 pounds there were a lot of things I couldn’t do, simple things that people don’t have to think about if they‘re not considered overweight," Rock told "Good Morning America." "I would have anxiety about taking the train because I’m taking up a seat-and-a-half. If I was on a plane I'd pretend like I was sleeping because my seat belt wouldn't fit."

"I like to use the analogy that I was living under water. I just got accustomed to it, even though it’s not normal," she said. "I’m now not underwater anymore."

Rock kicked off her weight loss by seeking support. She joined a program in Boston -- one that she still goes to this day -- that offers support groups, weekly weigh-ins and accountability with diet and exercise.

Through the program Rock learned tools to help her change old patterns and behaviors, which for her included not eating during the day and binge eating at night.

"I learned to time my meals three or four hours apart and I set alarms on my phone to remind myself to eat," she said. "And I went from eating a lot of carbs to eating low-carb."

Rock prepped her meals for the week on Sundays so she would always have healthy choices in her home. As the weight came off, Rock said she became consistent in exercising nearly daily and surrounded herself with people who supported her new habits.

"So much good has come from losing all this weight," she said. "I’ve found lifelong friends."

While Rock's before and after photos are what grab attention, she is focused on maintaining her weight loss and wants people to know the reality of the struggle that continues to be.

"I feel like losing weight was the easy part for me and the hard part is now maintaining," she said. "Sometimes I feel like my life has been consumed with just figuring out how to not get back to 350 pounds."

Rock has worked hard to look beyond a number on the scale, she said. She and a friend started the Bra Run in Boston, a race where women run in only their sports bras to promote body acceptance.

"To me it’s not about a size, it’s just about being comfortable," she said. "You should love your body regardless of the weight that you are and be comfortable and confident in the body that you’re in because it does so much for you."

For others inspired to start their own wellness journey, Rock shared these six tips.

1. Have a board of directors to support you: "Having people around you who are supportive, whether a program like I did or a therapist, or friends and family who can keep you accountable, because your worst enemy in this can be yourself."

2. Just start: "Literally just take the first steps."

3. Diet before exercise: "I say to focus on diet first. Once you are consistent for a month or two, then you can add in exercise."

4. Find a way to be active that you love: "Find what makes you happy. You don’t just have to go the gym and walk on the treadmill and be miserable if that’s not your thing. I love being outside."

5. Be consistent: "Even if you mess up, get back up right away. Don’t let months pass by before you try to get back."

6. Don’t be too hard on yourself either: "Be kind to yourself. You should be proud of yourself for wanting to take the first steps. You should be proud of yourself for wanting to be happier and healthier."

Editor's note: This was originally published on Jan. 20, 2020.