A landmark new study has provided the strongest evidence yet that a predominantly plant-based diet has less environmental impact than one that is high in animal products. In addition, the research indicated that organic food was also beneficial for the planet, but only for those who consume a plant-based diet.

The report, published in the journal Frontiers in Nutrition, involved more than 34,000 people and is the first to examine the environmental impacts of both diet and farm production systems. In addition, it is also the first to investigate the impact of organic food on the environment using actual observed diets rather than diet models.

Diets rich in animal products have a high environmental impact due to the significant energy requirements needed for livestock farming, the greenhouse gas emissions produced by livestock and the biodiversity loss resulting from the widespread conversion of natural habitats for feed crops.

Consequently, many organisations – including the UN's Food and Agriculture Organization – advocate for an urgent transition to more sustainable diets worldwide.

For the study, researchers collected data on food intake and organic food consumption in more than 30,000 French adults, ranking them using a so-called 'pro-vegetarian' score to determine their preference for either plant-based or animal-based products.

They then carried out environmental impact assessments of the production life cycle at the farm level using three indicators; greenhouse gas emissions, cumulative energy demand and land occupation.

"Combining consumption and farm production data we found that across the board, diet-related environmental impacts were reduced with a plant-based diet - particularly greenhouse gas emissions," said Louise Seconda from the French Agence De L'Environnement Et De La Maitrise De L'Energie and the Nutritional Epidemiology Research Unit, an author of the article.

"The consumption of organic food added even more environmental benefits for a plant-based diet. In contrast, consumption of organic food did not add significant benefits to diets with high contribution from animal products and only moderate contribution from plant products."

The researchers note, however, that the study was limited by the fact that production systems were not uniform across the world, and can be affected by climate, soil types and farm management practices.

"We didn't look at other indicators such as pesticide use, leaching and soil quality which are relevant to the environmental impacts of productions systems," Seconda stated. "Therefore, future studies could also consider these as well as supply chain and distribution impacts of food production."