Weight-loss surgery is an effective option for obese patients with type-2 diabetes, a New Zealand study has found.

In one of the first studies to look at the long-term effects of bariatric surgery in obese patients, Wellington Hospital endocrinologist Dr Richard Carroll reviewed the cases of 120 Kiwis who had bariatric surgery at least five years ago.

They found that patients lost on average 25 to 30 per cent body of their body weight following gastric bypass surgery, and maintained this weight loss over the mean follow-up period of 10 years.

"What generally happens with bariatric surgery is that people lose weight very rapidly, hitting their lowest weight at about 18 to 24 months," said Dr Carroll, who collaborated with fellow endocrinologist Associate Professor Jeremy Krebs and bariatric surgery pioneer Professor Richard Stubbs on the study.


"There might be a little weight regain after this initial period, but most people maintained most or all of this weight loss over the follow up period.

"Any weight regain didn't appear to relate to the length of follow-up or whether people had surgery five years ago or 15 years ago - their weight appeared to be reasonably stable."

Although there were extremes - some people lost a huge amount of weight and maintained that while others didn't lose much weight - no one was heavier at the final follow-up appointment than they were just before surgery, despite all patients being at least five years older.

This was in "complete contrast" to what was observed with non-surgical interventions, where weight loss was usually modest, and where any significant weight loss was all too often followed by weight regain, Carroll said.

Further, many of those who had type 2 diabetes before surgery had found the condition was resolved afterwards.

Of those with type-2 diabetes before surgery, a quarter had normal glucose tolerance by the end of the study, while another 47 per cent of the patients had also shown improvement.

"To put that into context, only 5 to 10 per cent of patients who receive traditional medical interventions might normalise their glucose tolerance in the most rigorous clinical trials - and less than that in the real-world setting."

A large proportion of the 28 per cent of patients who still had type 2 diabetes at the end of the Health Research Council (HRC)-supported study also saw improvements.

At the time of their surgery, more than 90 per cent of this group were on medications for their diabetes to lower glucose.

But by the time of the study follow-up, only 42 per cent still needed to take these medications and only one person required insulin.

"Most of us agree that the majority of what we see early after bariatric surgery can be put down to restricting calories," Carroll said.

"However, there are some other features going on too - particularly in terms of how the body handles glucose - that are different from what we observe after non-surgical weight loss."

HRC chief executive Professor Kath McPherson said a number of diabetes and obesity societies around the world were now recommending bariatric surgery as an intervention.

Because there were significant associated costs associated, it was important to have long-term data to show that the health and economic benefits of these surgical procedures outweigh the initial expense, she said.

"Obesity and diabetes cause significant health problems for many New Zealanders, and place a considerable strain on our healthcare system," McPherson said.

Obesity was a risk factor for diabetes, cardiovascular disease, musculoskeletal disorders, and some cancers.

Complications from diabetes included increased risk of cardiovascular disease, nerve damage, and damage to organs with kidney failure being a very severe consequence.

"Investing in research that finds ways to prevent and address what are frequently debilitating, disabling and devastating health issues is crucial if we want fewer New Zealanders to experience these health issues and have optimal health and wellbeing."