The little known side-effect of losing weight: divorce.

It took almost two decades for Kate Williams to agree to marry her boyfriend Phil. It wasn’t because she had any doubts about their relationship, it was because she couldn’t cope with the thought of having to wear a wedding dress at her size.

“I couldn’t bear to be seen bursting out of a huge wedding dress,” she told UK newspaper ExpressSo she got a tummy tuck and a boob lift, lost an incredible 63 kilos, and walked down the isle healthy and proud.

Then the trouble began. Her new husband became insanely jealous of all the attention Kate was getting due to her new body, particularly from other men. “But I started to get more attention when I was out and Phil became jealous,” she said. “I kind of started becoming more of his possession than his wife.”

Kate and Phil are now in the process of getting divorced, after just two years of marriage. Kate has a new boyfriend, Jack, who is supportive of her in every way possible. “I’m happier than I have been in years,” she said.

You might be tempted to judge Kate's former husband, however his reaction to her radical change is common. When it comes to any kind of extreme makeover of a partner's appearance, many struggle to cope.

I went on my own weight loss journey in my early twenties and something similar happened to me, except it wasn't as extreme as Kate's. Firstly I only lost 20 kilos, not 63 and secondly, there was no plastic surgery involved, just lots and lots of lovely new clothes in much smaller sizes that I had ever worn before.

When I first set out on my weight loss journey, it never occurred to me that my boyfriend might feel insecure if I lost weight. I was "chubby" when we met and he was super fit, constantly cycling and surfing. I couldn't believe he wanted to date me. We just clicked. Eventually we moved in together and he encouraged me to take up some exercise, but he never once commented on my eating habits. I would have died a thousand death's if he did. If anything, he encouraged me to eat as much as I wanted, as long as I agreed to join him cycling the next day.

I lost the weight and my boyfriend was my biggest supporter. We'd roller blade together and go to the beach and eat healthier food.

In the end I didn't lose the weight for him. I lost it for me, and because I was offered an incredible job that I wanted to look my best for. I lost the weight and my boyfriend was my biggest supporter. We'd roller blade together and go to the beach and eat healthier food. We'd also indulge from time-to-time with the running gag that he'd take the biggest serving of ice cream to "support me in my weight loss efforts".

As a result of my weight loss I became more outgoing. Where as previously we'd be happy to eat take away at home watching reality shows, I wanted to put on some of my new clothes and go out all the time.

My boyfriend pointed out to me that more men were paying me attention. I hadn't really noticed. The only attention I was interested in receiving was from my boyfriend. He confessed that he felt a bit insecure. While he was fit and healthy, he was a decade older than me. He said he was worried I'd leave him for someone younger. I laughed it off at first but then I realised he was being serious.

I went out of my way to reassure him that he was the only one for me and that one of the best things about losing weight was sort of matching him. Before I always felt like the fat chick standing next to the really hot bloke, with everyone wondering what he was doing with me. Now I felt as though I looked good together.

Reality TV shows like Bulging Bridges took advantage of some women's desires to slim down ahead of their big days. Article continues after this video.

Video via Slice

Psychologist Rebecca Cushway from Careers Excelled says that while reactions like this to extreme weight loss in relationships aren't normal, they are common. "In a healthy relationship both partners would want the best of the other partner and feeling healthy and good about yourself would be a part of that."

She is right about reactions like this being common. To lose the weight I used a food delivery service which worked really well because my boyfriend and I were working really long hours and didn't have a lot of time to shop for food and cook. I became quite close to one of the women who worked for the company and when I confided in her the problems my weight loss had caused in my relationship she said it was quite common and that the company often received angry phone calls and email from boyfriends and husband who were upset that their girlfriends and wives had lost a lot of weight and started going out more often.

Many relationships broke down as a result of one of the partner's dramatic weight loss. As far as I was concerned, any relationship that would break up over someone improving themselves was probably doomed from the beginning. Whilst a little insecurity seems fine and normal, some of the husbands were angry and offended that the person they'd initially hooked up with had gone and changed on them.

Cushway says oftentimes it's not the partner who decides to end the relationship but the person who has undergone the transformation. "Many would argue that someone who has struggled with long term weight issues and has successfully managed to lose the weight has probably had a shift in their our self-perception. It is not uncommon in that process to evaluate relationship which can also change the dynamic of the relationship which could impact both partners."

Then there are the scenarios like my own when someone is left feeling less. "Other theories talk about co-dependence and power in relationships. Perhaps the partner who didn't lose the weight now doesn't feel needed by the other partner and has not found a way to contribute." This was certainly the case with my boyfriend and I. After being my weight loss buddy and my fitness coach we found ourselves on more equal footing and it took us a little bit of time to find out how to navigate that.
For Kate, it became more sinister. Cushway says that for some is is about losing control over the partner. Kate's reference to her former husband treating her as a "possession" and his extreme jealousy certainly points to that.