Cost and greenhouse gas emissions of current, healthy, flexitarian and vegan diets in Aotearoa (New Zealand)

Abstract

Objective

To compare the costs and climate impact (greenhouse gas emissions) associated with current and healthy diets and two healthy and environmentally friendly dietary patterns: flexitarian and vegan.

Design

Modelling study

Setting

Aotearoa (New Zealand).

Main outcome measures

The distribution of the cost and climate impact (kgCO ₂e/kg of food per fortnight) of 2 weekly current, healthy, vegan and flexitarian household diets was modelled using a list of commonly consumed foods, a set of quantity/serves constraints for each, and constraints for food group and nutrient intakes based on dietary guidelines (Eating and Activity Guidelines for healthy diets and EAT-Lancet reference diet for vegan and flexitarian diets) or nutrition survey data (current diets).

Results

The iterative creation of 210–237 household dietary intakes for each dietary scenario was achieved using computer software adapted for the purpose (DIETCOST). There were stepwise differences between diet scenarios (p<0.001) with the current diet having the lowest mean cost in New Zealand Dollars (NZ$584 (95% CI NZ$580 to NZ$588)) per fortnight for a family of four) but highest mean climate impact (597 kgCO ₂e (95% CI 590 to 604 kgCO ₂e)), followed by the healthy diet (NZ$637 (95% CI NZ$632 to NZ$642), 452 kgCO ₂e (95% CI 446 to 458 kgCO ₂e)), the flexitarian diet (NZ$728 (95% CI NZ$723 to NZ$734), 263 kgCO ₂e (95% CI 261 to 265 kgCO ₂e)) and the vegan diet, which had the highest mean cost and lowest mean climate impact (NZ$789, (95% CI NZ$784 to NZ$794), 203 kgCO ₂e (95% CI 201 to 204 kgCO ₂e)). There was a negative relationship between cost and climate impact across diets and a positive relationship within diets.

Conclusions

Moving from current diets towards sustainable healthy diets (SHDs) will reduce climate impact but generally at a higher cost to households. The results reflect trade-offs, with the larger constraints placed on diets, the greater cost and factors such as nutritional adequacy, variety, cost and low-emissions foods being considered. Further monitoring and policies are needed to support population transitions that are country specific from current diets to SHD.