Switching to greener diets can help cut emissions – but may also spell higher food bills for families who can afford it least, a first-of-its-kind Kiwi study finds.
The University of Auckland researchers behind the analysis say their findings show that if Kiwis are expected to shift to more sustainable diets, it needs to be affordable.
In the study, published in the journal BMJ Nutrition, Prevention and Health, the researchers calculated the cost and climate impact of four diet scenarios: current, healthy, flexitarian and vegan.
They recommended plenty of fruit and vegetables, grain foods, some milk, legumes, nuts, eggs and poultry and fish, and less than 500g of cooked red meat each week.
The other two diet scenarios were based on the Eat-Lancet Commission's "Planetary Diet", with "flexitarian" leaning mostly toward plant-based foods, and vegan being wholly based on them.
Study lead author Bruce Kidd said New Zealand needed to transition to a planetary diet, as the country's food system contributed to around half of our emissions, and poor diets were a large part of our health problems.
"However, we know that insufficient income and the cost of food are large influences on food choices."
In assessing each of the four diet scenarios, the researchers modelled multiple possible meals for a family of four over a fortnight.
"Each scenario had constraints on the number of serves of each food that was allowed and had to meet criteria on healthiness, for example, a maximum limit on the salt content."
As well, the team collected food prices from online supermarkets, and also calculated emissions from a recently-published life-cycle assessment database of different food and drink items in New Zealand.
Household food waste data was also included to account for the emissions associated with wasted food.
The results revealed that moving from current diets to more sustainable and healthy diets came with higher mean prices.
While a typical Kiwi diet cost the least of the four – around $584 for a family – it came with the highest mean climate impact, or 597kg of carbon dioxide equivalent (kgCO2e).
A healthy diet cost slightly more over a fortnight - $637 – but also had a slightly smaller carbon footprint of 452kgCO2e.
Yet the prices of the other two were much higher - $728 for flexitarian and $798 for vegan – although their climate impacts were as low as 263kgCO2e and 203 kgCO2e respectively.
"This was striking but predominately due to the increasing cost of dairy alternatives, larger servings of fruits and vegetables, and some plant-based protein alternatives, such as falafel and burger patties."
Kidd added that alcohol and takeaways, which accounted for about 27 per cent of household food spending, weren't included in any of the diets.
If they were, the "current" diet would've been more expensive than what was calculated in the study.
Elsewhere in their analysis, the researchers found that, within each diet type, households are generally able to reduce diet costs by increasing the proportion of plant-based foods.
"This includes foods such as beans and lentils which are low cost, have significantly lower [emissions] than animal-based products and are a healthy addition to any meal."
The study also pointed to some notable trade-offs.
"One of these included the trade-off between healthiness, cost and low emissions food such as substituting dairy milk for soy milk which was more expensive and supplemented the nutritional benefits of dairy milk, but had fewer emissions."
But ultimately he said, the findings pointed to concerning issues around equity – particularly for families that wanted to eat greener.
"For example, a household transitioning from a current to flexitarian diet would spend $144 more each fortnight, with the climate benefit of 334 kgCO2e less emissions," he said, adding this was far higher than the current price of carbon.
"There are food choices that you can make that are cheap, healthy and good for the environment such as substituting meat for beans or lentils, and increasing seasonal vegetables and whole grains.
"But we need to advocate to the Government for action to help everyone in Aotearoa, especially those who are the most disadvantaged, to make the transition towards sustainable healthy diets.
"As guided by the articles of Te Tiriti o Waitangi, this requires transforming our food system to ensure it protects and enhances the health of our people and planet and empower communities to have self-determination."
The study follows Otago University research that found that eating less red meat could be key to New Zealand not only significantly slashing emissions, but also saving billions of healthcare dollars over coming decades.
Specifically, they showed a population-level shift to diets rich in plant foods such as vegetables, fruits, whole grains and legumes could — depending on the extent of changes made — cut diet-related emissions by between 4 and 42 per cent annually.
More strikingly, if all Kiwis adopted an exclusively plant-based diet tomorrow, and avoided wasting food unnecessarily, we'd achieve what would be equivalent to a 60 per cent drop in emissions from cars.
As a bonus, Kiwis could collectively enjoy up to 1.5 million more "life years" — that's those equivalent to a year of optimal health — and save our health system between $14 billion and $20b over the lifetime of our current population.
There are already plenty of signs that a green shift is happening.
By 2016, the proportion of Kiwis who stated that all — or almost all — of the food they ate was vegetarian had grown by nearly a third from four years earlier.
The sharpest rises came from among 14- to 34-year-olds, North Islanders and, perhaps surprisingly, men.
More recent polling by Colmar Brunton indicated that about one in 10 of us were now largely shunning meat, amid a growing shift to sustainable lifestyles.