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(CNN) -- In January, Carol Highsmith, 68, began a journey of threes. She had three milestones of 50 that she planned to reach by following three simple rules:
At 175 pounds, the 5-foot-1 Highsmith was at her heaviest weight. She vowed to lose 50 pounds so she could fit into a 50-year-old dress from high school. Determined to stun all her old classmates, Highsmith saw her invitation to Minnehaha Academy's 50th reunion as the catalyst to spark a lifestyle change.
Voted "Most Mischievous" by her classmates in 1964, the Takoma Park, Maryland, resident was determined to reclaim some of her youth.
"I wanted to go back [to high school] as I left," she says. "Still having fun in life... looking slim and feeling as good as I did back then."
Looking back, Highsmith would never have predicted she'd have weight problems.
"If I had seen a photo of myself as I look right now ... I would have died of embarrassment!"
But though she was thin, her eating habits were far from healthy.
"In my teens, I would go on all sorts of diets -- one time all I ate was hot dogs -- to make sure I fit into all my pretty dresses."
Once she started her career, those bad choices began to take their toll. She started to travel a lot and it became easy to eat what she calls "road food" frequently.
"I remember my first bite of a Krispy Kreme donut. It was heaven! I wanted more and many. One time I did a photo shoot at a Krispy Kreme place and they gave us two dozen donuts. I ate five in one sitting."
Her poor eating habits caused her health to slowly deteriorate -- both mentally and physically. She began to feel so self-conscious about her body that she only wore polyester pants and would never tuck her shirt in for fear of showing just how much weight she had gained.
When she received news of her upcoming reunion, Highsmith vowed to follow what she called the "WWW Plan" so that she could wear her favorite high school dress again.
Her first step was watching what she ate. She tried to eat only 1,300 calories per day of almost entirely unprocessed foods.
Step two was walking. She purchased a step tracker and made sure to log 10,000 to 25,000 steps per day, even if that required her to walk the halls and stairs of her hotel late at night.
The last step was drinking lots of water. She began to drink five to six bottles a day to ensure she was staying hydrated in the midst of all of her walking.
Complicating her mission, Highsmith knew she was going to be on the road during the months leading up to the reunion, working on a photography project for the Library of Congress, capturing photos of 21st century America for the Prints and Photographs Archive.
She would also be staying busy with her This is America! Foundation, which she founded to capture and catalog hundreds of thousands of photos of "slices of American life threatened by technological change, rampant development and widespread cultural homogenization."
She had to customize her weight loss strategy to her nomadic lifestyle. Although gas stations full of candy and other unhealthy snacks beckoned, Highsmith fought cravings by carrying unsalted nuts, canned baked beans, unsweetened Greek yogurt and fresh fruit.
For breakfast, Highsmith would generally eat fruit, poached eggs, ham and a little milk and coffee. Protein was key for keeping her full well into the afternoon.
Lunchtime was a less structured meal. Highsmith made a point to never eat lunch "just because it was lunchtime," but to wait until she genuinely felt hungry. Then she would eat some yogurt, fruit and nuts, or a fresh salad.
For dinner, she usually ordered grilled fish, sweet potatoes and vegetables. Sometimes she would allow herself to splurge on a carefully measured pat of butter for her sweet potatoes.
"Every time I thought about not walking all the steps or not drinking the water or having just one extra handful of nuts, I thought about how much fun it (would) be to go the Minnehaha Academy reunion and look like a million," says Highsmith.
Between her healthy eating habits and being constantly on her feet, Highsmith watched as the pounds melted away.
"Every day that I follow my weight loss plan I am thrilled," Highsmith wrote to CNN in the middle of her journey. "All of it helps me feel better about myself. When I look in the mirror and see a slimmer me, I am more confident and know I look good in my clothes."
She was careful, though, not to get distracted from her main goal: her health.
"I eat only when I am hungry, but if I get hungry, I need to eat," says Highsmith. "I am not on a starvation diet -- I am on a healthy, let me lose this weight and live longer journey. I never mention the word 'diet.'"
When the day of her 50th high school reunion arrived, Highsmith was ready and eager to show off her new physique. Her classmates were stunned with her transformation.
"I was very impressed," says former classmate Linda Bjorklund, who has stayed in touch over the years. "She was very disciplined about her food intake and her exercise. Carol usually does whatever she sets her mind to doing ... she always gives everything 115%."
Highsmith's message to her classmates? "Find a way to turn back the clock and wake up feeling good every day."
At 130 pounds, Highsmith's journey is not over. She plans to lose 20 more pounds by her birthday in May 2015, vowing to continue eschewing sweets, walking at least 10,000 steps per day, and eating and drinking properly.
But she is in no rush to see the numbers on the scale go down.
"I am not trying to lose it fast because I did not gain it fast," says Highsmith. "We are what we eat and I have decided for the rest of my life that if something goes into my mouth, it must be good for me."