A few days after my 21st birthday, I glanced through the dozens of photos that had been taken. More than 150 of my family and friends had gathered to help me celebrate. I should have been smiling with delight as I flicked through the shots. Instead, I was fighting back tears.

A couple of weeks later, I went to see my GP for a routine check-up. After taking my blood pressure, her face was serious. ‘It’s very high,’ she explained. ‘It’s not good for you.’ Stunned that I could have worryingly high blood pressure so young, I asked what I could do. And, in all kindness, she told me the best thing would be to lose weight.

I knew there and then that I didn’t want to spend the rest of my life feeling unhealthy and unhappy. And if I wanted to do something about it, I’d need to make some real changes.

In 2010, I started university, studying for a degree in technological education. By then I was a size 20-22 and weighed around 18st. I’d moved to Glasgow, some 100-odd miles from our family home in rural Castle Douglas, and, as a country girl, I felt lost in such a big city. Because Mum was no longer cooking my dinners, I started relying on ready meals, plus two or three chip-shop or Chinese takeaways a week.

I found myself struggling to fit in socially, too. Despite the distance, I’d end up going home almost every weekend to see my family and my boyfriend, Steven.

Life begins at... 21

It was with that 21st birthday revelation, in March 2013, that everything finally changed.

I decided that joining a Slimming World group would suit me best... and my timing couldn’t have been better – a new group was starting in Castle Douglas. In June 2013, I decided to give it a try and convinced my best friend, Lizzie, to come along.

I wasn’t sure what I weighed. I hadn’t stepped on the scales in years and was absolutely mortified when 17st 5½lbs flashed up on the screen.

My Consultant, Grant, was extremely sensitive and kind, reassuring me that soon this number would be a thing of the past.

That night, I left group and went straight to my nearest supermarket. Instead of my usual pile of ready meals, I filled my trolley with punnets of blueberries, strawberries and grapes, along with bags of fresh vegetables, Free yogurts, lean meat and jars of dried herbs and spices. It was the healthiest food shop I’d ever done!

From then on, I was hooked. I discovered loads of recipes, such as Diet cola chicken and Slimming World curries. It made me realise that I didn’t need to get a takeaway – I could make healthier versions that were just as delicious.

Because I was enjoying all these tasty new foods, I found it easier than I’d expected to stick to the plan 100 per cent... and in a week I’d lost 8½lbs.

For the first time I could remember, I felt really proud of myself, and pleased with what I was eating. It was just the inspiration I needed to carry on going week after week.

When I did go back to uni that September, I’d already lost nearly 3st. I couldn’t believe I’d changed my body that much in just one summer... it felt amazing. My friends complimented me on my slimmer figure and a few of them almost didn’t recognise me!

Becoming me

With every half-stone I lost, I felt so much happier. My mood was the best it had been since I was a child. And I got the clothes-shopping bug!

My energy levels increased and my biggest dream, to play netball again, finally came true. I joined a local team near home, and this time I wasn’t at all self-conscious – I actually felt really good!

To my delight, in August last year, I reached my target of 11st 5½lbs – something I’d once thought was impossible. Since then my weight has fluctuated a little. It doesn’t worry me, though – ultimately, I’m the one in control of it and I know exactly how to get right back on track again.

Health-wise, I’m in a much better place. I no longer have high blood pressure.

I’m now a technology teacher at my old school. As well as being slimmer, I’m so full of energy and I’m constantly smiling. The pupils laugh at me as I never sit still during a lesson – I’m always up and down and dashing between the tables.

For a long time, it was as though my personality had gone into hiding. Now, I feel like the real me. And do you know what? I really like her!

My stay-on-track tips

Kirsteen shares the little things that have helped her on her weight-loss journey.

  • Draw up a meal plan every week, before doing your shopping. It really helps me stay on plan, as I know exactly what I’m eating each day and won’t get caught short.

  • When you’re going to a restaurant, check out the menu online beforehand if you can.

  • Use social media. I love Instagram and post my meals every day (@healthy.happy.teacher) – a bit like a food diary. It keeps me motivated and I get lots of tips and new ideas from followers.

  • Keep your eyes on the next prize. As a teacher I know how motivating an award can be, and that was definitely my own experience as I worked towards the next half-stone award.

  • Treats are important, and they don’t have to be food! I’ll go shopping for clothes, make-up or a blingy piece of jewellery as a reward for staying focused, or as a little pick-me-up. I think it’s just as important to be kind to yourself when you’re having a tricky week as when you’re feeling great.

*Weight loss will vary due to your individual circumstances and how much weight you have to lose.