The Essex brunette - who has just topped the country music charts with her two new music singles - was recently the target of cruel comments after snaps showed her looking slim while filming her new reality show.
Explaining she was 'in and out of hospital' prior to filming her show There's Something About Megan, the 24-year-old didn't hold back as she described battling with the lifelong illness, coeliac disease - the real reason for her weight loss.
Coeliac disease is a common digestive condition where the small intestine becomes inflamed and is unable to absorb nutrients found typically in wheat, barley and rye.
Following the weight jibes from followers Megan hit back in the comments section, writing: 'So you lot would never bully someone about being over weight but think it's acceptable to call them anorexic and look like a skinny rat.
'When I have coeliac disease and problems with my stomach. #oneruleforone I eat a healthy amount of food a day, and I'm under the hospital. Leave me alone.'
One fan apologised once the star was very honest about her health implications: 'extremely sorry for calling you that! I actually thought you went down to this weight because you wanted to. Didn't know about the health issue ! I apologise'.
'Can't believe people are saying she looks too skinny 😂 everyone is built differently, and she has celiacs. Get a grip 🙄', said another fan.
Many followers were supportive of the reality star: 'I'm sure you know this already but don't listen to anyone negative I completely agree with you being called skinny hurts just as much as I'm sure it would to a bigger person being called fat,' one exclaimed to Megan directly. 'Keep strong and never feel the need to explain to anyone. Your stunning!! X'
'Women should be bigging each other up, not dragging one and other down. What kind of world do we live in! It's disgusting and embarrassing to read. @megan_mckenna_ you haven't got to explain yourself to anyone 🙂👋', argued another follower.
Talking to The Sun, Megan - who suffers from coeliac disease and has recently been diagnosed with Irritable Bowel Syndrome - said: 'It's not nice as no one would call someone fat, but they think it's OK to call me anorexic.'
She continued: 'I was so ill with my belly before I went to Nashville and I was in and out of hospital and no one knew what was wrong with me, so yes I was thin as I was unwell.
'People need to realise I'm always going to have problems with this and not troll me.'