The decline in heart disease has plateaued – is this due to changes in our diets?

Published: 28 September 2023

The progress made with heart disease over the past 50 years in New Zealand appears to be coming to an end, as the decline in heart disease plateaus for the first time in decades. Three researchers have been awarded funding by the Heart Foundation to investigate the impact of food on heart health and will dig deeper into the impact of different types of foods and diets and what can be done to reverse this unfavourable trend.

Impact of new diet trends

Dr Kathryn Bradbury, from the University of Auckland, will investigate whether new trends in diets are contributing to higher blood fats that could explain the plateau.

Heart disease rates in New Zealand peaked in the late 1960s before declining steadily in the decades following. The previous decline was explained in part by a move to a heart-healthy diet and subsequent declines in blood fats and blood pressure.

"The statistics are currently moving in an unfavourable direction," Kathryn says. "We saw gains made in the past few decades where people consumed a simpler, low-fat diet, including switching to consuming alternatives to butter. Today, high fat diets are more popular and there is some confusion around how healthy a higher fat diet is."

The popularity of low carbohydrate diets - typically low in fibre, and high in fat and protein - in many countries appears to be increasing, as does the perception that butter and saturated fat does not increase the risk of heart disease.

Kathryn will examine trends over the past 15 years in intakes of saturated fat, polyunsaturated fat, sodium, potassium and fibre, as well as food sources of these nutrients. She will work with Auckland and Northland lab data to examine trends in blood fat levels over the past 10 years.

"The research will help us to understand to what extent heart disease is due to changes in diets and help to inform effective strategies to improve heart health. Then we can determine whether advice and guidelines, policies and programmes need updating."

"I hope, through my research, to introduce strategies that could significantly improve the heart health of New Zealanders once again."

Kathryn spent five years at the University of Oxford where she was a nutritional epidemiologist at the Nuffield Department of Population Health. She worked on large population studies, including EPIC-Oxford, and in 2018 brought that expertise to New Zealand. The EPIC-Oxford study is a major long-term research project looking at diet and health.

Researching ultra-processed foods

Early career researcher Dr Kelly Garton, also from the University of Auckland, will investigate if ultra-processed foods, which are often energy-dense and high in salt, fats and sugars, and their link with heart disease.

Kelly's research will look into why ultra-processed food consumption became and remains high in the typical New Zealand diet. She will explore what the levers for change are and hopes there is an opportunity for the results to feed into initiatives to improve nutrition. 

She will undertake analysis of prices, sales, imports, exports, and investment in ultra-processed foods in New Zealand over the past 30 years, and the institutions, interests and ideas driving their consumption.

Her findings will help inform a new understanding around ultra-processed foods and their consumption in New Zealand.

"By reducing policy inertia, and increasing the focus on disease prevention through healthier food environments, we may be able to go back to reducing the rates of heart disease morbidity and mortality," Kelly says.

"Over time, reducing incidence of these diseases in the population will allow people – especially those most affected such as Māori, Pasifika, and people in lower socioeconomic groups – to lead healthier, happier and longer lives."

"My research will highlight barriers to regulating unhealthy, ultra-processed foods and beverages, identifying strategies to overcome them, and present a roadmap for reducing consumption in New Zealand."

Deeper dive into school children's diets

With a focus on the younger generation, Dr Kathryn Beck, from Massey University, has received funding to investigate ultra-processed food consumption in 600 school children in Auckland and Waikato, and the potential contribution to poor heart health.

Over the past 20 years, there have been significant changes to the food environment and an increase in ultra-processed foods, which have little nutritional value and are high in ingredients that are harmful to health.

Many studies have shown that eating high amounts of ultra-processed food increases the risk of heart disease, obesity and diabetes, but there hasn't been any research done in New Zealand on the impact of ultra-processed foods on the health of children.

In a New Zealand-first study, Kathryn will investigate what and how much ultra-processed food tamariki are eating, explore what nutrients they are getting from foods, where they are getting ultra-processed food from, and the context in which ultra-processed foods are being eaten.

This research will also look at the impact of Ka Ora, Ka Ako (the Government's school lunch programme) on food intake and towards the nutrient intake of tamariki.

Kathryn says finding out this information will help to improve the diets of school children and in turn, improve their heart health as adults. Altering ultra-processed food intake is a translatable strategy to improve the future generations of New Zealanders.

"Ultra-processed foods are everywhere you look – supermarkets, dairies and school tuck shops. They're convenient, accessible and often cheaper. I hope that in future we can help kids to make the healthy choice, the easy choice." 

Heart Foundation Medical Director Dr Gerry Devlin says there have been global studies strongly linking ultra-processed foods to high blood pressure and heart disease, but there has been little research done here which specifically relates to our population.

"The research we're funding will hopefully help develop strategies and inform policy to enable a healthier future for all New Zealanders," he says.