A mum who weighs a whopping 273kg is planning to almost double her size to become the world's fattest woman.

American Donna Simpson is determined to pile on the pounds in her bid to reach 450kg in only two years.

The 42-year-old mum-of-one insists she's healthy, despite needing a mobility scooter to leave the house, reports the Daily Mail.

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Donna, who lives in New Jersey, already holds one record - in 2007 she became the world's fattest mother when she gave birth to daughter Jacqueline. She needed a team of 30 medics to help with the risky C-section but found her way into the Guinness Book of Records as a result.

Now she's making a bid to become the largest woman on the planet - despite only being able to move six metres before she gets out of breath and has to rest.

"My favourite food is sushi, but unlike others I can sit and eat 70 big pieces of sushi in one go," Donna, who wears XXXXXXXL dresses, told the UK newspaper. "I do love cakes and sweet things, doughnuts are my favourite."

To achieve her larger-than-life goal, Donna says she needs to eat up to 12,000 calories a day (the average recommended amount for women is 2,000.)

So to fund her hefty $750 weekly food shop, she runs a website where men pay her to watch her eat fast food.

But don't expect her long-term partner Phillippe to tell her to slim down, adds the paper.

The pair met on an online dating site for plus-sized people and Phillippe, who is a self-confessed fat admirer, actively encourages her to eat more.

Donna insists she isn't sorry for her weighty goal, despite the pressures it is placing on her body and the risks to her health.

"I love eating and people love watching me eat," she adds. "It makes people happy, and I'm not harming anyone."