Publicly funded surgery for New Zealanders struggling with serious obesity is a "postcode lottery".

That's according to a University of Auckland-led study showing "extreme inequalities" for accessing bariatric surgery by geographic region.

The University's associate professor of endocrinology, Rinki Murphy, said the surgery, which includes stomach stapling and gastric bypass, is the most effective treatment for obesity.

"It leads to lasting weight lost, improved quality of life, remission of type 2 diabetes and reduced heart disease and cancer risk," Murphy said.

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Yet, in some regions of New Zealand the operation is more accessible than other areas.

Researchers compared the region's population with the number of people who were seriously obese, and stacked those figures up against the number of surgeries each DHB was performing each year, between 2012 and 2014.

They also looked at the Ministry of Health's target number for the number of surgeries that should be performed at each DHB.

Murphy said the findings were shocking because the study revealed the number of surgeries performed at each District Health Board did not align with their population prevalence of morbid obesity.

"At the moment, your chances of getting bariatric surgery are influenced by where you live," Murphy said.

She compared Canterbury DHB to Waitematā DHB. Both regions had a similar population and morbid obesity rate but the number of surgeries being done at Waitemata was far higher.

In 2012, Waitematā's population was 439,850 and the number of people with a Body Mass Index (BMI) over 40, which correlates to being morbidly obese, was 11,788.

Between July 2013 and June 2014, 104 surgeries were performed - against a Ministry of Health target of 36.

In Canterbury, the population was 411,690 at that time and 11,857 had a BMI over 40.

Only 13 surgeries were performed, against a Ministry of Health target of 3.

This shows that you are considerably more likely to be able to get the surgery if you live in the Waitematā region, than if you live in Canterbury.

In Waikato, there were a lot more people who were morbidly obesity (17,732) but far fewer surgeries being done (18).

Canterbury DHB's executive director planning, funding and decision support Carolyn Gullery did not think there was a "postcode lottery", saying each South Island DHB had its own strategy for population health and surgery was just one solution.

"Examining the use of one separate surgical solution is not telling the full story in the context of all the Canterbury Health System tries to do and has done to maintain or minimise the rate of obesity within its population," she said.

Renda Ranzow before her surgery.
Renda Ranzow before her surgery.

She said all five South Island DHBs pooled their bariatric funding and the most in-need patients throughout the South Island received the surgery.

"All DHBs agree that, overall, the South Island region is better off if we use our bariatric funding in this manner.

"However this does mean the most in-need patients don't always reside in Canterbury DHB's catchment area, which would affect our delivery if you looked at isolated years," Gullery said.

Waitematā and Canterbury DHB were funded the same for bariatric surgery from the Ministry of Health for the 2013/14 year, Gullery said.

The Ministry of Health's acting manager of electives and national services, Simon Duff, said DHBs were responsible for assessing the needs of their populations and providing the appropriate mix of planned care services to address those needs, including bariatric surgery.

"All patients referred for publicly funded bariatric surgery are prioritised on the National Bariatric Prioritisation tool, a set of criteria which scores patients' need and ability to benefit," he said.

The ministry did not hold information on the number of people being referred for bariatric treatment. "This information is held locally by District Health Boards."

The cost of the surgery through the publicly funded system, is around $15,000.

Murphy said most DHBs delivered a higher number of surgeries than the Ministry of Health funded targets.

Overall New Zealand's national rates of public-funded bariatric procedures at 2.7 per 1000 morbidly obese patients is less than half the rate in the UK and Australia.

"The health system needs to respond to the rising numbers of people affected by obesity," Murphy said.

"We need to work harder to eliminate inequalities by geographic region, and to provide better and more transparent approaches to prioritising patient selection for this limited resource, along with more research to understand how to best serve our populations."

Renda's story:

Renda Ranzow says her quality of life has improved drastically after bariatric surgery. Photo / Doug Sherring
Renda Ranzow says her quality of life has improved drastically after bariatric surgery. Photo / Doug Sherring

Until 2009, Renda Ranzow led a relatively healthy life.

She was able to play soccer with her grandkids, felt happy in her own body and getting out of the house to exercise wasn't a problem.

Then, she was diagnosed with type two diabetes, started taking insulin and everything changed.

"I was battling with my sugar intake so I gained a lot of weight, I was very tired all the time and became depressed.

"I didn't want to go out. My quality of life was not good and my family was worried my diabetes would get so bad I might need a foot amputation or something," Ranzow told the Herald.

The 65-year-old Aucklander was offered publicly funded gastric bypass surgery last year - though it was not an easy process.

Every month she had to attend group sessions with bariatric nurses, psychologists, dietitians and other patients to make sure she was up to it.

"[They] explained what was going to happen over and over again, and each time I was given the opportunity to opt out," Ranzow said.

But she had already tried many diets and was becoming increasingly concerned about her long-term health so opting out was not an option for her.

"I knew this was what I wanted," she said.

For the three weeks leading up to the surgery, Ranzow was only allowed to have protein shakes.

In that time she lost 9kg. Then, after the surgery, which she had in February, she could only eat pureed food for three weeks.

Before the operation she weighed 125kg. After she weighed 104kg and is expected to lose a further 20kg.

"Getting that surgery has been life-changing. I am having fun for the first time in a long time. I feel a lot calmer and I'm able to enjoy time with my family, who have been so supportive."