Teenager Libby is desperately unhappy and believes her weight is the reason why.
The 14-year-old weighs 22stone 8lbs - almost double her sister, Issy, who at just 19 months older is a slim 12stone.
Libby, from Gosport, Hampshire, has been badly bullied because of her size with people making fun of her double chin and callig her a "whale.
And her self-image and confidence have taken a serious pounding
Libby admits: "I hate myself. I don't like my body, or my legs, or my arms, or my double chin.
"I just feel everyone judges me - even my family."
And Libby copes with the heartbreaking bullying by comforting eating, which makes her problems worse.
Overweight since she was a child, Libby, who loves to snack on whole loaves of bread, places the blame for her size firmly at her parents' door.
But she has a plan - she wants to overhaul her diet and for her family to join her in her weight loss journey.
The family's efforts are shown at 9pm tonight on 5Star's It's Your Fault I'm fat.
In an emotional message to her parents, Lisa and Bill, and sister, Issy, Libby says: "I sometimes feel like you are embarassed of me and you feel Issy is the perfect daughter and that you show her off more than you show me off."
She says the fact her parents used to lock treats in the garage made them more desirable and lead to the start of her problems.
Not only that but there are FIVE fridges in the family home, each one stuffed full of food.
Mum, Lisa, is utterly heartbroken at her daughter's admission and the whole family instantly agree to support her in her diet journey.
But Lisa, who herself used to be obese and still weights 16stone, is also at a loss as to how her two daughters have such different figures.
She says: "I've brought two children up withi 19 months of each other and done all the same things.
"How is it that one is overweight and one isn't?"
But both Libby's dad, Bill, and her sister, Issy, have a different theory as to why the teenager is struggling with her weight.
Issy says: "Libby does like to pass the blame, nothing is ever her fault."
And Bill adds: "Libby doesn't know when to stop eating hen she's full, whereas Issy will stop when she's full."
Although Libby is determined to prove her family wrong and says she's "excited" with her new regime - even when she learns she'll be swapping her 4,000 calories a day feasts for just 1,500.
Her parents will also be embarking on a strict fasting diet, where they eat just 500 calories a day for two days a week.
And the whole family will be embarking on an exercise programme with personal trainer, Becky, while Libby has been told to use her trampoline and walk 10,000 steps a day to boost her weight loss.
Despite a positive start with dinner and an exercise session, the family run into problems on day one of the challenge when Libby and Issy share an entire loaf of French bread between them.
The setback leaves a devastated Lisa in tears and Bill describing the girls' behaviour as "madness".
And during the first two weeks, Libby struggles to get on board with the weight loss plan - admitting she had a pizza on a night out with friends and tucking into a Subway salad with Caesar dressing and a packet of crisps.
But then personal trainer Becky steps in with a one-on-one session and reveals she used to weigh 18 stone.
It's a huge moment for Libby who finally finds her motivation.
She says: "Becky sharing her story with me has been really inspirational because it shows you can lose the weight."
The next few weeks are a new Libby, with her making sensible diet choices and exercising whenever she can.
And it pays off, not least with her relationship with her mum.
As a birthday treat in week four of the six week challenge, Lisa and Libby treat themselves to a girls' pamper day.
Libby says: "I can't thank you enough for making me do this and for helping me."
There's an even bigger surprise later that night at LIbby's birthday party - the outfit she has ordered is too big and has to be tied at the back to make it fit.
It's also in a pretty pink colour, something she would never have considered a few weeks ago when she would drown her frame in baggy, black clothes.
To help her stick to her diet, dad Bill has created a birthday cake out of tiny cupcakes so she can havea treat and not bust her calories.
And then the family's six weeks are up.
Bill had shed an impressive 9lbs, dropping from 24stone 9lbs to 24stone.
Lisa has lost almost a stone, dropping from 16stone to 15stone 1lb.
But it's Libby who's seen the biggest change.
The teenager has dropped from 22stone 8lbs to 21stone 11lbs - and she's delighted.
She said: "I can see changes in my face and in my waist. I feel so confident about myself and I'm actually looking in the mirror.
"I can't wait to see where I am next year."
But there's a bigger realisation - that she was the one responsible for her weight gain, not her family.
Libby said: "I was blaming my mum but this has made me realise that I'm the one who controls what I put in my mouth so it's no one else's faul but mine.
"I feel bad for blaming everyone else becayse they just want the best for me."
It's Your Fault I'm Fat is on 5Star at 9m tonight.