Shifting to healthier diets is also better for planet health, simulation research flags

29 Mar 2024 --- Using a computer model, researchers determine that a flexitarian diet increases the feasibility of reaching climate goals set in the Paris Agreement, most notably staying within a 1.5°C temperature increase. At the same time, they caution that considerable challenges still need to be addressed in policies supporting healthy diets, social inclusion and compensation schemes. 

According to the report, if the world shifts to a flexitarian diet such as the EAT-Lancet Planetary Health Diet by 2050, greenhouse gas (GHG) emissions will be reduced. These reductions would increase the compatible carbon budget, allowing the world to achieve the same climate outcome with less carbon dioxide removal and less stringent CO2 emission reductions in energy, reducing pressure on GHG prices, energy prices and food expenses. 

“We find that a more sustainable, flexitarian diet increases the feasibility of the Paris Agreement climate goals in different ways,” says Florian Humpenöder, a scientist at the Potsdam Institute for Climate Impact Research (PIK) and co-lead author of the study. 

“The reduction of greenhouse gas emissions related to dietary shifts, especially methane from ruminant animals raised for their meat and milk, would allow us to extend our current global CO2 budget of 500 gigatons by 125 gigatons and still stay within the limits of 1.5°C with a 50% chance.” 

Healthier diets 
In the study published in Science Advances, PIK scientists investigated how dietary shifts would contribute toward the feasibility of staying within the 1.5°C increase, comparing scenarios with and without a global shift to flexitarian diets in 2050. 

As a model for healthier diets, they used the EAT-Lancet Planetary Health Diet, shown in earlier research to align with climate needs.

Co-author Isabelle Weindl from PIK comments: “The EAT-Lancet Planetary Health Diet is a flexitarian diet predominantly featuring a wide variety of plant-based foods, a marked reduction of livestock products especially in high- and middle-income regions, and restricted intake of added sugars, among other things.” 

However, the diet has also faced criticism in recent years due to its high content of phytate — an anti-nutrient found in plants — and dietary gaps in six essential micronutrients: zinc, iron, calcium, folate, vitamin A and vitamin B12. 

If the global population shifts to a flexitarian diet by 2050, it is more feasible to stay within the 1.5°C increase.The report also compared the costs of healthy diets to current diets, suggesting that in upper-middle to high-income countries, more nutritious diets are 22–34% cheaper, while they are 18–29% more expensive in low and lower-income countries, currently including a population of over three billion people. 

In these countries, the researchers suggest that shifting to healthier diets requires additional support, such as transfer payments or (revised) food distribution schemes. However, the study does not account for such transfer schemes or their potential costs. 

Sustainable impact 
According to the report, shifting to flexitarian diets could increase the economic and physical feasibility of 1.5°C pathways. 

Earlier this year, PIK researchers argued that a food system policy overhaul could mitigate climate change, as food systems are “destroying more value than they create.” Despite pledges, GHG emissions from the meat and dairy sector are still rising yearly, according to research released last year. 

“Our results show that compared to continued dietary trends, a more sustainable diet not only reduces impacts from food production within the land system, such as deforestation and nitrogen losses. It also reduces GHG emissions from the land system to such an extent that it cuts economy-wide 1.5°C-compatible GHG prices in 2050 by 43%,” explains co-lead author Alexander Popp, leader of the working group land-use management at PIK. 

“Moreover, healthy diets would also reduce our dependence on carbon dioxide removal in 2050 by 39%,” he adds. 

Policy recommendations 
At the same time, the study authors caution that implementing healthy diets at a global scale faces considerable difficulties. Decision-making in food policies is often dispersed across institutions and ministries, which hinders a coherent implementation of policies for healthier diets. In addition, social inclusion and compensation schemes are essential to transition to these diets, especially in lower-income countries. 

Implementing healthy diets at a global scale requires food policies, social inclusion and compensation schemes.The model presented also does not account for transaction costs for policy making, implementation and monitoring. 

The report includes several recommendations based on available research on actionable strategies for dietary shifts. For example, adding a high tax on beef and lamb meat, which have the highest GHG emissions across all animal products, could contribute to emission reductions while being less controversial than taxing all meat consumption.

According to the report: “Even more promising are policy instruments that, rather than changing the monetary incentive structure, change food environments (e.g., food provision in canteens and food distribution schemes) or target the preferences of consumers as such (e.g., advertisement bans, education, or nutrition counseling).” 

The authors emphasize that more research on policy instruments targeting food environments and consumer preferences is needed. 

“The results indicate that a shift in our diets could make a considerable difference if we do not want to crash through the 1.5°C limit in the next 10 to 15 years. This calls for globally concerted efforts to support the transition toward sustainable healthy diets,” concludes Johan Rockström, PIK director and co-author of the study. 

By Jolanda van Hal