"I know you want to look your best on your wedding day," the trainer responded.
"If you don't hire me hire someone else. Those pictures last centuries. Your children's children will still have those pictures. You want to be the best you."
Young proceeded to smack down the trainer, calling him out for shaming her body which she admitted has taken "a long time" to love.
"I will look my best because I'll be so happy I get to marry the man I love," she responded.
"I know it's probably hard for you to understand this, but it's taken a long time for me to love my body. I am constantly shamed or reminded that I am heavy and should be embarrassed.
"The idea of me being embarrassed by my wedding photos because I might be 'fat' in them and people centuries from now will be ridiculing me? That's the insinuation and I say f**k that noise."
But instead of accepting Young's rejection - the trainer hit back.
"You can accept how you look but you can't be happy with the way you look," the trainer wrote.
"You can't lie to yourself.
"I just wish the whole big body acceptance people would accept the fact that they are not happy with their bodies...I have been there I know how it is that's why I can comment so openly about it."
Young questioned the trainer as to why she shouldn't be happy with her body, and that she felt "sad" that the person behind the messages was "wrapped up" by appearances.
"Not everyone wants to be chained to that insecurity," she wrote.
"You are projecting your feelings of your former fat self into every fat person and suggesting they should feel bad, and it's perpetuating a cycle of self-loathing that we're being taught by society.
"Once you see the truth - that it doesn't define you or devalue you - you'll realise that being fat doesn't define you or devalue you."
But again, the trainer responds - suggesting she will feel bad based off her wedding photos.
"It isn't society that tells us we look bad," the trainer said.
"We all have a conscious. You can see yourself in your wedding dress and know you don't like it not based off society but based off what you see.
"When it comes to "fat shaming" you can only be shamed if there is something to be ashamed of. When you get to the point where you have no conscious then you have no shame.
"When I look at your Twitter and Instagram you have so many posts about food. And it's all bad food. You love food and you know that's not the right way to live. So you feel ashamed."
Young's constant response is what angered 31-year-old - and prompted her to share the exchange with her 24k Instagram followers.
"I'm posting this because I want every woman and man to know that it does not MATTER what you look like," she wrote.
"You are worthy. Love is out there for you. Life is waiting with open arms. It doesn't matter if you're skinny or fat or between the two or willowy or broad shouldered or peer shaped or like a board or anything in between. You get good stuff in life by being YOU.
That's what matters."
Her post, which has received more than 1600 likes and 300 comments was met with praise and appreciation from her followers.
"Preach sister! What a chump this guy is," one person wrote.
"As a person that teaches fitness, trains people and competes, this is deeply upsetting. Almost unbelievable!" another added.
"This just made me cry. So proud of you for standing up for yourself instead of letting them bully you and feel sorry for yourself."
