A foul-mouthed New Zealand surgeon has been reprimanded after swearing at a severely obese patient.

A 44-year-old mother filed a complaint about the doctor after a tense consultation with him last year, reports.

The doctor said f--- at least three times to the Maori woman after she told him she didn't like the word "diet" and preferred the term "lifestyle".

He told her she was, "going on a f---ing diet".

In the letter of complaint, the woman wrote: "[The doctor] said if I couldn't handle the word diet then he challenged my motivation and stated that I would never survive surgery because I was still bullshitting myself and therefore my thinking was still f---ed".

In response to the woman's concerns, the doctor said they no longer had a "therapeutic relationship" and scratched her from the gastric bypass waiting list.

New Zealand's Health and Disability Commissioner, Ron Paterson, said the doctor, who admitted using bad language, had been unprofessional and insulting.

AAP