Amanda Townsend, 45, wrote an open letter 'To the couple in Sports Direct Blackpool at 12.30 on Sunday who totally belittled me' on her Facebook page, making it clear how much their words had hurt.
'I just wanted to say how much your cruel snigger and whispers to your wife upset me, not just upset me a little bit but has made me feel totally and utterly crap inside and out,' Amanda wrote.
'Yes I am a huge size 22 and weigh 20 stone and yes I was wearing Nike pink patchwork running leggings and pink Asics trainers and I was looking colourful with red rosey cheeks but what you didn't realise was that I had just ran a 10k race 15 mins earlier, also that I have only been running for the last 7 months and have lost a massive 6 stone in that time!'
She then recalled how she had confronted the pair, who 'shot off at a rate of nots looking shocked and embarrassed'.
'So next time you feel the need to be horrible to ANYONE please think before you look at someone and whisper to your wife to look too. Fat people have feelings too you know.'
Since Amanda shared her emotional post at the end of April, it has received over 2,700 shares and hundreds of supportive comments applauding her positive attitude and dedication to exercise.
'Good on ya you're doing fantastic and look great. To hell with those ignorant very sad people,' one said, while another agreed, 'People are so narrow mined and cruel. But what you have achieved is commendable. Keep it up. Well done.'
'I was really upset. I wasn't just wearing running pants and a training top for fashion reasons. I was probably still purple from the run,' Amanda later explained.
'I know I'm fat but at least I'm doing something about it. There was no need for this couple to make comments like that when they clearly don't know how hard I'm working.
'I did the London Marathon in 2005 when I was 24 stone and it took me eight hours, but I still did it. Now I get up at 4.30am every day and run 5km.'
However, despite her initial devastation at the jibe, Amanda, who trains with her twin daughters Lisa and Megan, added that the response to her message had been 'overwhelmingly positive.'
'The running community is really friendly and I think people can see that I'm actively trying to do something about my weight.
'I've had 3,200 messages from people and it's been shared more than 2,000 times. Maybe the message will get back to the person who said it.
'We were so buzzing after the race and what this man said left me feeling like I'd been kicked in the face. It's sad that someone feels the need to do that.'