Aucklander Katie Jones doesn't mind sharing her story. "I could go on forever about my weight loss and exercise programme as it has been a big part of my life for the past few years," she says proudly.

The research manager has lost 40kg in the past two years. She went from not being able to run at all to completing 10km races. In 2010, Jones was 130kg and a size 22. Last week, she reached 89kg and is now a size 14 for the first time in 15 years. These days the feeling of getting out for a run is "just brilliant".

"I always feel like I have accomplished something at the end of a run," she said. "Whether it is a short, fast run or a long run where I am trying to go a certain distance, I always feel proud of myself."

What was the catalyst for your weight loss?

The true catalyst was falling pregnant with my son almost three years ago.

Before that my weight had yo-yoed since my teens and in January 2010 I saw some photos from a friend's wedding that really hit home to me just how much weight I had put on. I decided then to lose weight but, to be honest, I did not really commit. A year later I found out I was pregnant and the health implications of my size really hit home. My pregnancy was not going to be easy due to my size - I was close to 130kg. I was told to not put on any weight and, unfortunately, I still developed gestational diabetes. I was forced into a good eating plan. I swore I would maintain that once my son was born.

You lost 40kg in two years, how did you achieve this?

My son was born in October 2011. And I kept my promise. Three months after he was born I was 10kg lighter than my pre-pregnancy weight. I walked a lot, I watched what I ate, however, I still tried my best to be healthy - I needed to for my son.In January 2012 I joined Weightwatchers. My good habits were starting to slip a little. I have been on Weightwatchers online ever since. Initially, eating well and occasional walking was enough for me to lose weight. However, over time it became harder. Last summer I began walking three to four times a week for an hour at a time. In March 2013, I felt my fitness was good enough to start the Couch to 5km programme. In nine weeks I went from not being able to run 1km to running for 30 minutes. From there I concentrated on extending my time, and with the support of my best friend Denise Lotze as a running buddy, we signed up to the Onehunga 10km as a goal.

Did you think losing this amount of weight was going to be possible?

I hoped it was possible but it was such a huge goal that I don't think I ever fully comprehended just how much weight it was. I had set myself a goal of 90kg initially, and I just tried to keep losing weight each week, even if only 100g. I still have 10-15kg to lose. That seems much harder than the initial 40 to be honest.

How hard has it been keeping it off and maintaining your fitness?

This has always been a lifestyle change. I try not to diet or do things I can't maintain. That is why I took up running this year. I needed a form of exercise that I could walk out my front door and do in 40 minutes. I don't do well in gyms - I can't commit when I have to travel. I am also vocal about my goals. I have the support of all my friends and family and my husband is constantly reminding me to go for my runs. The more I lose the more motivated I feel. It is an amazing feeling to be able to run for an hour, knowing a year ago I would have laughed if anyone had suggested that.

How hard was it at the start to get into the fitness?

Very hard. It felt like a chore and in the beginning I was not fit enough to run so I had to commit to walking for over an hour. With a young family that was hard work three to four days a week. And not very satisfying. Now I am fitter and I have achieved some of my goals I find regular exercise enjoyable.

It must have been pretty special when you completed a 10km race?

I did not believe until the ninth kilometre that I was actually going to finish the race. Denise was running it with me and we kept encouraging each other. At the finish line we were pretty emotional. It was a first for both of us, and made more special because we did it together. I still want to shout my accomplishment from the rooftops! I even followed it up with an 8km race a week later.

How has your weight loss changed your life?

It is almost indescribable how much my life has changed. I have more energy. I sleep better. I am happier. My self-confidence has also improved, which has benefited both my personal life and my work.

What is it you enjoy about running or trail running?

The immediate sense of accomplishment. There is always a new goal to work towards. Just a little bit faster, or a little bit further, or a new environment to explore.

What advice would you offer people who are looking to lose weight?

Take it slow. Set gradual goals. They don't have to be big. I started off with small things, like not taking the lift at work and committing to exercising in some form three times a week. Make sure you can maintain your diet beyond weight loss. And try different things - some people love gyms, some don't. Figure out what you enjoy. And don't give up when setbacks occur. My weight plateaued for three months at one point - I lost less than 1kg. But I kept going, tried different things, and asked my friends for help.