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"International research has highlighted the climate and health co-benefits that arise from consuming a diet that is rich in plant foods like vegetables, fruits, whole grains and legumes.
"We wanted to understand if this holds true here in New Zealand, and to tease out which eating patterns could offer the greatest co-benefits in this context."
The research team developed a New Zealand-specific food emissions database that, in estimating greenhouse gas emissions arising from foods commonly consumed here, considered important parts of the life cycle of each food, including farming and processing, transportation, packaging, warehousing and distribution, refrigeration needs, and supermarket overheads.
Using its database, the team was then able to model climate, health, and health system cost impacts stemming from a range of dietary scenarios.
As a general rule, the climate impact of animal products, particularly red and processed meats, tended to be substantially higher than that of whole plant-based foods, including vegetables, fruits, legumes, and whole grains.
"Fortunately, foods that are health-promoting tend also to be those that are climate friendly. Conversely, certain foods that carry known health risks are particularly climate-polluting. Red and processed meat intake, for instance, is associated with an increased risk of cardiovascular disease, type-2 diabetes and certain cancers," Dr Macmillan said.
The research ultimately showed that a population-level dietary shift could, depending on the extent of changes made, offer diet-related emissions savings of between 4% to 42% annually, along with health gains of between 1million to 1.5million quality-adjusted life-years (a single quality-adjusted life-year is equal to one year of optimal health) and cost savings to the health system of $14billion to $20billion over the lifetime of the current New Zealand population.
Mr Drew said the analysis revealed emissions savings equivalent to a 59% reduction in New Zealand’s annual light passenger vehicle emissions could be possible if New Zealand adults consumed an exclusively plant-based diet and avoided wasting food unnecessarily.
"All of our scenarios were designed to meet New Zealand’s dietary guidelines."
The pair began with a baseline scenario where they looked at minimal dietary changes required, relative to what New Zealanders were consuming now, to meet the guidelines.
"These changes included increased intake of vegetables, fruits, whole grains and milk, along with decreased intake of highly processed foods. From there, we tailored our dietary scenarios to be progressively more plant-based — that is, substituting animal-based foods with plant-based alternatives.
"We thought it was important to show what was possible if people were willing to make changes to their eating pattern, and what would be possible if our entire population made a significant shift in that same direction," Mr Drew said.
"As our modelled dietary scenarios became increasingly plant-based and therefore more climate-friendly, we found that associated population-level health gains and healthcare cost savings tended also to increase."
A scenario that replaced all meat, seafood, eggs, and dairy products with plant-based alternatives, and that also required people to cut out all unnecessary household food waste was found to offer the greatest benefit across all three of these parameters.
Mr Drew said this was exciting because we could now better understand what it meant to promote a climate-friendly eating pattern in the New Zealand context.
"Essentially, the message is highly comparable to that being delivered in other countries already, and we should be rapidly looking for ways to effectively support our population in making eating pattern changes."
The researchers argued the findings should prompt national policy action, including revising the New Zealand dietary guidelines to include messaging on climate-friendly food choices.
They also advocated for the implementation of other policy tools, such as pricing strategies, labelling schemes, and food procurement guidelines for public institutions.
"Well-designed public policy is needed worldwide to support the creation of a global food system that no longer exacerbates the climate crisis, or the burden of non-communicable disease," Mr Drew said.