WASHINGTON (CNN) -- Growing up, Heather Davis wasn't the kind of kid people would have called fat or even chubby.
Heather Davis weighed 250 pounds and wore a size 22 at her heaviest. She lost 110 pounds and wears a size 4.
Like many children, Heather studied hard, did her homework and played sports after school. During elementary school, she remembers being thin -- but things started to change as she approached adolescence.
"My bad eating habits began during my 'latchkey kid' years," says Davis. "In high school and middle school, I played sports, but with a diet of Doritos and soda for lunch ... large family dinners ... I became overweight."
During her senior year in high school, Davis, who is 5 feet 9 inches tall, weighed 200 pounds.
"We had a meat-and-potatoes family. We had dessert every night and I was a member of the 'clean your plate club,' remembers Davis. "It caught up with me."
By the time she was 22 and attending graduate school, Davis' weight had ballooned to 250 pounds. Davis says her weight gain was caused by major life transitions -- triggered by emotional eating, a junk-food diet and lack of exercise.
Davis dreaded shopping for clothes and said she found it hard to find stylish, age-appropriate clothing for her bigger body. She says it was a struggle to look neat and put together as most of her shirts "hugged every roll." Looser-fitting clothing, she says, made her feel as if she were wearing a tent.
The additional weight also began to take a physical toll. Everyday tasks such as walking up stairs or in the shopping mall started to become difficult. Davis says she was constantly hot and any physical exertion would cause her to sweat, even in below-freezing temperatures.
Life became a constant struggle.
"I would get hot a lot because of the extra weight I was carrying. Picture yourself with a 100-pound backpack on," says Davis. "That was what it was like climbing the escalator. My knees hurt. My back [and] shoulders hurt a lot."
Davis, who lives in Washington, says she had tried everything to lose weight, such as low-carb and low-fat diets and even starvation. But one day, something clicked.
"I was on the campus shuttle and saw the Gold's Gym," Davis says, "And, I said 'I can go down into the Metro and go home and eat my Ben & Jerry's [ice cream]. Or, I can go over there and really do this. Just do this!'" Watch Davis' dramatic weight loss transformation
1. Never let anyone tell you "You can't." Yes, you can.
2. Get as much social support as possible. Going to the gym with others is fun and motivating.
3. You will not be the biggest person in the gym and everyone will not be staring at you.
4. Some thin people in the gym used to be really heavy and they will applaud you.
5. Lose weight for you. Not because someone else tells you to. Also, know when to stop losing.
6. If you lose your way (fall off your diet), get right back into the saddle and try again.
7. Keep a calendar. Mark off every day you exercise and eat right. You will see the days rack up, and it will make you proud.
8. When you do lose weight, save one item from your heaviest weight. Look at it when you feel discouraged and you'll see how far you've come.
9. Don't let friends or family derail you. If you don't want to eat something, it is OK to politely decline, but don't go crazy. You don't want to be "that person" at the lunch table.
10. If you want cheesecake or a sweet treat -- eat it in moderation. Don't deprive yourself of anything or you will get discouraged.
Davis remembered her grandmother -- with whom she'd been extremely close -- who had died from heart failure brought on by years of unhealthy eating and lack of exercise.
"She will never get to see my wedding, children or experience other joys in her life," Davis says.
Davis says there wasn't any defining experience or "lightbulb" moment that forced her to make a change. It was the realization that after years of failed diets and the physical toll of obesity, she'd had enough.
During her first visit to the gym, Davis says she could barely handle 15 minutes on the treadmill. But she stayed on track by reminding herself that weight loss was going to be hard work and there was no easy way out.
She did cardio exercise for two weeks and began modifying her diet by cutting out starches, ice cream and pizza. Within the first two weeks, she had lost 8 pounds. She was motivated by the positive results and gradually increased her cardio, incorporated weight training and continued to change her diet.
Davis remained determined, and over the next 12 months, with the support of her family and regular check-ins with a gym trainer, she lost 110 pounds.
She went from wearing a plus-size 22 to wearing a size 4 or 6. The weight loss and healthier lifestyle boosted the 31-year-old's self-confidence and gave her access to a richer, fuller life.
"My days of treating my body badly are over," says Davis. "I focus on things I enjoy such as European travel, language classes and beach vacations."
Staying healthy for Davis means eating in moderation and incorporating fun forms of exercise into her daily life. She no longer owns a vehicle and enjoys long walks in downtown Washington.
She's also set another goal for herself -- a second graduate degree -- which she hopes will allow her to help others.
"I'm working on my master's in public health because all of this health awareness has made me want to help other people," Davis says. "Obesity is reaching epidemic proportions and I will take pleasure using both experience and scientific knowledge toward planning and evaluating programs designed to help people incorporate healthy behaviors into their lives."
Davis is training to run a half-marathon and is running up to 6 miles. She says even though she's lost 110 pounds, she's still the same person -- outgoing, and more importantly -- happy.
She's also become an inspiration for people who desperately want to lose weight.
"If I can do it, anybody can do it," says Davis.
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Matt Sloane contributed to this report.