What dietary factors determine the difference between self-selected nutritious diets that protect the environment versus those with an adverse impact?

Many dietary guidelines are currently revised to consider environmental concerns. To inform these revisions, the aim of the present study was to describe the dietary factors that distinguish nutritious diets protective of the environment from nutritious diets that adversely affect the environment.

Individual self-selected diets from a representative sample of French adults were classified according to their nutritional quality (assessed through nutrient-based indicators) and their environmental impact (assessed through an indicator called the Product Environmental Footprint single score). Diets which combine the best nutritional quality and the best environmental impact constituted the Nut+Env+ class and were considered "more sustainable". Their dietary characteristics were compared to those of diets from the Nut+Env- class (i.e., the best nutritional quality but the worst environmental impact) and from the Nut-Env+ class (i.e., the best environmental impact but the worst nutritional quality). All of the analyses were based on 2000 kcal adjusted diets.

The two classes of diets with the best nutritional quality represented 5.5% (Nut+Env+) and 11.3% (Nut+Env-) of the sample, respectively. They were both in line with guidelines for a healthy diet regarding fruits and vegetables (more than 400g/2000 kcal) and dairy products (between 2 and 3 portions of dairy products/2000 kcal), as well as regarding sweet and salty food and beverages (low amounts). However, the “more sustainable” diets (Nut+Env+) had an environmental impact 46% lower on average than the Nut+Env- diets. The only statistically significant differences between those two classes of nutritious diets regarding their food contents were that the Nut+Env+ diets contained much less ruminant meat (7.4g vs 62.8g/2000 kcal), less seafood (30.0 vs 56.1g/2000 kcal) and more whole grains (42.9g vs 19.8g/2000 kcal), but also (slightly) more sweet and salty foods (107.9 vs 73.4g/2000 kcal) than the Nut+Env- diets. Diets from the Nut-Env+ class had the lowest environmental impact but their food content was in contradiction with dietary guidelines with, notably, low amounts of fruits and vegetables (236g/2000 kcal) and high amounts of sweet and salty food and beverages (317g/2000 kcal).

This study confirmed that nutritious diets are not necessarily environmentally friendly (and vice versa). Moreover, it showed that, among self-selected nutritious diets, only amounts of certain foods, in particular ruminant meat, seafoods and whole grains distinguish nutritious diets protective of the environment from nutritious diets that adversely affect the environment, suggesting that these foods should be particularly looked at when including environmental considerations in the revision of food-based dietary guidelines.