Radio stars Chrissie Swan and Meshel Laurie have taken aim at fitness expert Michelle Bridges over her claim she has never met anyone who is morbidly obese and happy.

Bridges, who stars on The Biggest Loser weight loss reality show and has been described as Australia's most influential health and fitness expert, made the remarks on Monday night's Australian Story.

The comments sparked fiery debate on social media, with users accusing the star of fat shaming, and also drew criticism from former Biggest Loser host Ajay Rochester, who accused her of being "fat-phobic".

"It might be seen that I have this agenda on people who are overweight or people who are deemed fat," Bridges said on the program, during which she also spoke about becoming a mother and her fight against the sugar industry.

"Honestly, if you are happy where you are, more power to you.

"But I can tell you, I'm yet to meet someone who is morbidly obese and happy."

Melbourne-based Swan, a former reality TV star, questioned the remarks, saying she had known Bridges "for years".

Michelle Bridges has sparked controversy after an appearance on Australian Story ( Supplied: Michelle Bridges )

"Hi, Michelle, if you are listening, remember me? I've known you for years. We have met many, many times. You can take it back now. I'm happy."

The DJ said it was "equally ridiculous" to view all obese people as jovial, adding: "All we are saying is you should not judge someone's entire character by what they look like."

Comedian Laurie also addressed the remarks, saying that while they may reflect the feelings of Bridges' clients, they did not reflect those of society as a whole.

"[Bridges is] in the business of meeting people who have come to her because they are unhappy," she said.

The KIIS 101.1 DJ also mentioned a conversation she had recently had with her young son.

"He said to me, 'mummy, you're fat'. I said, 'Yeah ... and that's OK. I'm really happy. I'm a really happy person'. I meant it from the absolute pit of my soul," she said.

"I'm such a lucky person. I've got two arms that work, two legs that work. A brain that's sharp.

"It is actually possible to be fat and happy, I promise you."

Rochester accused Bridges of making bigger people feel worthless, and said everyone had ups and downs in life, regardless of their weight.

"Do NOT let this woman tell you that you are not worthy simply because of your weight or the space you take up. That's her problem not yours," Rochester wrote on her blog.

Bridges has not responded to the criticism.

You can watch the Australian Story episode on ABC iview.