Nearly 100 pounds lighter than the day her beloved sister passed away from complications of epilepsy and morbid obesity, Medford resident Jennifer Cook has made dramatic changes to her own health in a quest to show her children a better way to live.

Nearly 100 pounds lighter than the day her beloved sister passed away from complications of epilepsy and morbid obesity, Medford resident Jennifer Cook has made dramatic changes to her own health in a quest to show her children a better way to live.

From an overweight child to an uncomfortable, 5-foot, 222-pound adult in 2002, the 39-year-old has spent the past decade transforming her body into that of a 120-pound fitness instructor and competitive bodybuilder.

Born in Medford, Cook grew up on a farm eating large quantities of meat, fried foods, processed snacks and "lots and lots of soda."

"The way I grew up was, 'Clean your plate,' meaning if it's on your plate, you eat every bite," she says.

"It wasn't, 'Eat until you're full or eat nutritious food,' which is much healthier. By the time I was 8, I was overweight, and I didn't know why. I had no idea I was being overfed."

Because of her family's poor eating habits, Cook and her sister developed similar body types and health concerns. Cook's epiphany came with the death of her sister, Meegan, in 2005.

"When my sister died, I was sitting with her autopsy report, and it said that basically her morbid obesity contributed to a myriad of medical issues. She was epileptic, too, but her obesity was a major contributing factor," Cook says.

Pregnant with a son, Cook adopted her newborn nephew after Meegan died, leaving her with five children to care for.

"It was like, 'Oh, my God, I have to get my weight under control. If I don't, I'm going to die and be only 30 years old and leave all my kids without a mother. And I can't help them be better if I don't make me better,' " she recalls.

Starting gradually, Cook lost small amounts of weight by learning about healthful eating and becoming more active. An invitation from a friend to work out at Rogue Valley Family YMCA — child care provided — spurred Cook to use the facilities regularly and begin taking classes.

As her weight dropped, Cook became almost addicted to her new lifestyle.

"Once you start exercising and you realize the physical changes that it's making, it does give you this euphoric feeling, and it releases endorphins," she says.

"After you get over the part where it feels like it hurts, it feels like it's what you're supposed to be doing to be healthy. The way my life is now, even when I go on vacation, I find some way to fit in exercise wherever I'm at."

When she became pregnant with a son in 2009, Cook continued her exercise routine throughout her pregnancy and "hit the gym again, three weeks after he was born."

The busy mother's constant presence in YMCA fitness classes led to an opportunity to become an instructor.

With her burgeoning health and commitment to exercise, Cook, however, still didn't realize how far she had come. Attending a bodybuilding show in support of a friend, Cook declared to YMCA trainer Tammy Miller, "No way would I ever get up onstage and have people gawk at my body!"

"But she said, 'You know you have the body type for this, right?' And she stood me in front of a mirror and asked, 'What do you see?' " Cook says.

"I just laughed her off at the time, but I realized I really hadn't looked at myself in the mirror — and I mean really looked at myself — and acknowledged my changes."

What she saw really opened her eyes.

"It didn't happen right away, but I put a bug in her ear and just waited. She finally came to me and said, 'OK, I'm ready. Let's do this,' " Miller says.

With one competition under her belt — Cook also competed in an Ironman event in May — she's already looking toward her next competition.

"I knew she'd get the bug once she started this," Miller says. "The first time she got up on that stage, she was just a natural. Her stage presence is phenomenal, which is usually something that has to be learned."

Jeni Beck, fitness director for Rogue Valley Family YMCA, says that given Cook's predisposition to obesity and other health concerns, her commitment to change is especially inspiring.

"Jen doesn't have genetics on her side, but one thing I think she really has going for her is that she does really enjoy exercising. Some people really struggle with exercising or diet. Jen is just consistent and faithful with both her exercise and her diet, and she wouldn't have the results she has without both those things," Beck says.

"You obviously can't pick your genetics, and they play so much into what you're going to look like and how hard you're going to have to work. Jen is proof that if you want something badly enough, and you have the discipline, you can accomplish your goals."

In spite of what she's accomplished for herself, Cook says her proudest accomplishment is helping others to achieve better health.

She says she occasionally gets confused looks from people who knew her in what seems like a past lifetime, when she wore size-22 clothes.

"People who only knew me heavy are a little shocked, and a lot of them don't even recognize me. I was in Walmart one day, and a girl who grew up right next door to me walked right past me," Cook says.

"So I said, 'Hi.' And she looked at me like I had three heads."

Now a mother of six, Cook says she looks forward to living — rather than wondering whether she will.

"Now I don't have to worry about if I'm going to live longer than my kids or wondering if I'll be healthy enough to enjoy watching them grow up," she says.

"It's like marking one of those things off the list. I'm healthy and fit. No way am I ever going back!"