It wasn't until a girlfriend pointed out on social media "that bump is organs".
"So, that bump? It SHOULD be there and it isn't wrong," she wrote.
"A girlfriend posted this in the SociEATy recently and I realised that there is SO many people who don't realise this!
"Our stomachs? They shouldn't necessarily be flat! That's your uterus (and fat and other organs obvi like intentioned, stomach, etc, let's not get too into anatomy here. Simply saying our tummies and pelvis house V important things) down there!"
"Welp, the answer is part of that bumps is organs."
However, people bombarded her post to tell her she was wrong, including medical experts.
"Fat is 100 per cent normal, but saying the bump is your uterus just simply isn't medically accurate," UK doctor Joshua Wolrich responded.
"I don't think it's getting 'too into anatomy' to point out that this simply isn't true," another follower demanded.
"Your uterus sits below the pubic bone until about 12 weeks' gestation, so the uterus itself does not make a bump unless you are pregnant.
"But there ARE other organs there and also fat that is intended to protect those organs so the bump is still absolutely normal," the follower continued.
A woman who said she was a gynaecologist, wrote: "Unless your uterus is enlarged somehow — fibroids, post-partum, etc — this isn't true," while a midwife told Colleen it was "belly fat".
The US nutritionists' post also attracted the likes of British comedian Sofie Hagen, who shared the post on Twitter, with a sarcastic caption.
"Hey, not to brag, but apparently I've got a pretty huuuuuuge uterus. You may now no longer call me fat. I am #UterusGifted," she said.
One woman replied: "It's definitely not her uterus. The bladder sits on top of your uterus, so it's just a load of wee she's holding in!"
Colleen, who referred to her friend's uterus claim as "mind-blowing" is yet to respond to the feedback.
Some, however, believed the claims writing: "Wait what. This explains SOOO much. It doesn't matter how many crunches, etc I do, it's always there. Well, now I know why!"
"The womb tilts slightly forwards too which increases the bump. Great post," another agreed.
