Trial shows weight loss from plant-based diet

27 March 2017

With the highest obesity and Type 2 Diabetes rates in the country, Gisborne has been subject of successful new dietary study. 

MEDICAL research published this week in Nutrition & Diabetes journal shows Gisborne participants lost an average 11.5kg in one year, the largest weight loss of any randomised control trial where participants had no restriction on calories and did not have to exercise. 

Newshub video on the diet

The participants of the BROAD study, patients at City Medical, swapped their standard fare for a low-fat, whole-food, plant-based (WFPB) diet.

Gisborne has the highest rates of obesity and Type 2 Diabetes in New Zealand. The researchers, Gisborne GPs Dr Nick Wright, Dr Luke Wilson and study co-ordinator Morgen Smith (with oversight from Hauora Tairāwhiti public health physician Dr Bruce Duncan and GP trainer Dr Patrick McHugh), decided this made Gisborne perfect for a dietary intervention.

The BROAD Study targeted patients with obesity, or who were overweight and had heart disease or diabetes.

The 65 participants were split randomly into two groups.

Thirty-three participants ate a whole-food plant-based diet, and were compared with a control group of 32.

Foods eaten by the diet change group included: potatoes, pasta, beans, bread and spreads, soups, salads, stir fries and rice.

Participants following the whole food plant-based diet received cooking classes and lifestyle change education during the 12-week intervention.

Food was not provided, and participants were instructed to eat whenever they were hungry, and until they were full.

The diet programme excluded animal foods and refined oils, in favour of unlimited amounts of whole grains, legumes, vegetables and fruits.

Dr Nicholas Wright said the whole-food, plant-based approach shows very promising weight loss results that appear to be sustained over time.

“People don’t have to worry about going hungry and can still lose weight.”

At 12 months, as well as the weight loss, those who changed their diet decreased their waist circumference by an average of 9cm and their medication usage by an average of 29 percent.

Two out of four patients with diabetes reduced their dosage or reliance on diabetes medications, including one who no longer required insulin.

“We’re starting a second trial to look specifically at the benefits of a plant-based diet for people with Type 2 Diabetes,” said programme director Morgen Smith.

Future research will be funded by Turanga Health and Eastland Community Trust.

Dr Wright says not only is a plant-based diet great for health, it also reduces environmental impact by using less land and water.

During the study, environmentalists James Cameron (the noted film director) and Suzy Amis Cameron gave their support to BROAD study participants via a special video message.

The patients

The patients who agreed to be part of the trial had obesity, diabetes, heart disease or a combination of those. They came from all walks of life: farming, forestry, teaching, and retirees.

How many in the whole foods plant-based diet group?


How many in the control group?


Did all of the patients make it through?

At six months, eight people had dropped out from each group.

How long was the trial?

The article follows the effects over the course of one year.

Participants from the intervention group are being followed for three years in total.

What were the key findings for the whole food plant-based diet group?


  • Average 11.5kg weight loss at one year (25lb) which is greater weight loss than any other trial that does not limit energy intake or mandate regular exercise.
  • Improved self-esteem and quality of life.
  • Decreased medications from 94 across the diet group on a normal day to 67.
  • One patient out of four with diabetes was able to stop taking his insulin. Two of the four diabetics improved their condition to the point where they no longer met the diagnostic criteria for diabetes.


Could the plant-based diet participants eat as much as they wanted?

Yes. Participants were advised to eat as much as they liked, whenever they were hungry. Participants were provided with education but were responsible for making their own food choices.

Did they have to exercise?

No, exercise was not mandatory.

What, if any, dietary supplements were required?

Participants in the intervention group took 50mcg a day of vitamin B12.

What will the follow-up research look at?

Further research will be done into diabetes following promising results from our research and results from research done overseas.

Don’t all diets lead to weight loss if you stick with them?

Some diets that do succeed in the short-term often fail in the long-term or are not intended to be maintained. Participants in the BROAD study were introduced to and supported to make, a diet change. This change was intended to be able to be continued long-term.

Why is a plant-based diet more environmentally friendly?

A plant-based diet requires less farmland and water. Eating fewer animal products increases the number of people that can be supported by existing farmland. Growing fruit and vegetables doesn’t produce as much greenhouse gas as raising cattle or livestock.

Nutrition & Diabetes is a peer-reviewed, online, open-access journal bringing to the fore outstanding research in the areas of nutrition and chronic disease, including diabetes, from the molecular to the population level. See the journal article on The BROAD study: A randomised controlled trial using a whole food plant-based diet in the community for obesity, ischaemic heart disease or diabetes