While food production significantly contributes to this environmental footprint, the foods we choose to eat are just as important.
But it's easy to get bamboozled by all the conflicting advice out there about what to eat for nutritional reasons versus what to eat for environmental reasons.
In the middle of a cost-of-living crisis, our diets need to be affordable and, to ensure we can stick to them long-term, not too drastically different from what we are accustomed to eating.
Luckily, we know exactly what characterises a sustainable healthy diet.
The World Health Organization and the United Nations' Food and Agriculture Organization define sustainable healthy diets as "dietary patterns that promote all dimensions of individuals' health and wellbeing; have low environmental pressure and impact; are accessible, affordable, safe and equitable; and are culturally acceptable".
But designing diets that meet all these various, and sometimes conflicting, aspects is a complex problem which could take days, if not years, for the brain to solve.
That's why researchers at the Riddet Institute in New Zealand have taken a computer-based mathematical modelling approach to the problem instead.
Dietary optimisation modelling seeks to identify the best combination of foods to fulfil diet-related goals, such as meeting nutrient recommendations, while also adhering to certain conditions, such as cost and environmental impact limits.
It also allows researchers to design diets that meet all these conditions with a minimal shift from people's current dietary patterns and cultural preferences.
Dietary optimisation is hardly a new concept. It can be traced back to 1945 when economist Dr George J. Stigler tried to eat well while spending the least amount of money doing so.
Fast forward to today, and researchers are putting sustainable eating into action.
Imagine a tool that is accessible to everyone and can guide users — from conscientious consumers to policymakers — through the maze of diet advice and environmental worries.
The Sustainable Nutrition Initiative in New Zealand is developing an interactive dietary optimisation tool, called The iOTA Model, which will allow users to explore what it takes for a typical dietary pattern to be transformed into a nutrient-adequate diet and what the environmental implications of such a diet are.
All with minimal departure from the users' current dietary habits to ensure it will be easy enough for them to adopt the optimised diets without making too many changes to what they are used to eating.
Research suggests that optimising diets for nutrition and sustainability must have a country-specific focus to account for food availability, consumer habits and the dietary needs specific to different populations.
For example, when considering dietary habits in different countries, a one-size-fits-all approach may not always be appropriate: rice might be considered a staple in Nepal but potatoes make up the main energy source in Mexico.
The nutritional content of foods may also differ from place to place, especially when it comes to the micronutrients, as these are largely impacted by their growing environment.
We should also consider the differences between the nutritional requirements and dietary habits of people of different sexes and age groups — such as women of reproductive age needing more iron or elderly people needing more protein.
While this may all seem far too complex, if you're eating healthier and meeting nutritional recommendations, chances are, you are already eating better for the planet as well. For example, reducing your consumption of foods high in sugars and low in important nutrients, and replacing them with nutrient-dense wholefoods, is better for both your waistline and the planet.
What is consistent across almost all countries is that increasing the contribution of fruits, vegetables and starchy foods to the mix of foods we eat, while decreasing the contribution of sugar and fats, would help reduce diet-related emissions while providing essential energy and nutrients.
In other words, eating what we need and avoiding what we don't reduces some of our diet-related environmental impact.
It is important to note that even though animal-sourced foods are among those with the highest diet-related emissions, sustainable diets do not have to be exclusively plant-based.
A dietary simulation study in the UK showed that meat intake had to increase for a small number of people in the study in order to optimise the nutritional composition of their diets while still meeting the emission targets.
There is much more to the sustainability of our diets than only reducing the environmental impact.
Consumer wellbeing — from a nutritional, cultural, and economic perspective — should be at the front and centre of any efforts towards more sustainable diets.
This means food that is healthy, affordable but also respects the food habits of the culture it's part of.
Dr Mahya Tavan is a postdoctoral research fellow at Riddet Institute’s Sustainable Nutrition Initiative (SNi), hosted by Massey University in Palmerston North, New Zealand. She is working on the development of The iOTA Model, a dietary optimisation tool for designing sustainable diets that are nutritious, acceptable and affordable.
