Mark Mitchell distances himself from Judith Collins' obesity comments, Gerry Brownlee says his weight is his responsibility

National MP Mark Mitchell has distanced himself from comments made by Judith Collins and Gerry Brownlee about obesity, saying he thinks the issue is more nuanced than either politician claims.

On Tuesday Collins told reporters that obesity is a "weakness" for which people must take "personal responsibility" - comments which received swift backlash from health experts.

Mitchell told Newstalk ZB on Wednesday Collins' idea that obesity is a "personal choice" is partly true - "but it's a lot more complex than that".

"Some obesity is related to medical conditions, even psychological conditions that need treating, so it's a more complex issue."

But Brownlee, the party's campaign manager and deputy leader, agrees with Collins, saying his own obesity is no one's problem but his.

"To say that there should be some state-mandated action enforcing people to be a particular size, I think that's a step too far," he told Newstalk ZB.

Collins has also doubled down on her comments, telling The AM Show on Wednesday that "any decent GP will say it's not that complicated".

"It's all about what we put into our mouths - calories in and calories out. I realise that there are a very few number of people that have medical conditions that make them obese, but actually most of us, we have to take some personal responsibility... don't blame a system when it's not the system sticking the big carbs in your mouth."

Her comments have been widely condemned by health experts, with one telling Newshub it was "disgraceful".

Health advocate and obesity specialist Kate Berridge says the comments are "utterly simplistic and totally disrespectful".

She says the comments from Collins' show a "pretty unfair" view of a global problem.

"It's so much more complex than just 'step away from the pies' - it is going to take policy and attitude changes."

Collins' comments were also rejected by Jacinda Ardern, who also called them "simplistic".

"I think if you're so simplistic to call it an issue of collective responsibility then it will never be an issue that we can collectively resolve," she told Newshub.

"I think it's wrong, and if you talk to experts in the sector they would reject [those claims] and so do I."