According to the FAO, a sustainable diet is one that has little impact on the environment, is nutritionally adequate, culturally acceptable, and affordable. But are these criteria compatible? Researchers from INRA and the Aix-Marseille University1 have simulated the impact of cutting back on the greenhouse gases (GHG) of diets on nutritional quality and price.
To conduct this model-based research, scientists used data gathered from the French INCA2 study2 on the consumption of 1,899 adults. They crossed those figures with data on the carbon footprint of 402 of the most popular foodstuffs in France, the average price of each foodstuff, and indicators of its nutritional quality. The researchers defined and analysed three types of models:
- the first imposed no nutritional constraints (FREE), the only requirement being a gradual decline in greenhouse gas emissions with no change in calorie intake;
- the second model imposed a reduction in greenhouse emissions and maintenance of the macronutrient balance: proteins, lipids, carbohydrates (MACRO);
- lastly, a nutritionally adequate model (ADEQ) imposed not only an equilibrium of macronutrients but also maintaining the recommended dietary allowances in vitamins, minerals, trace elements, fibre, and essential fatty acids, and maximum recommended values for sodium, saturated fat, and free sugars.
The scientists found that with the FREE and MACRO models, the reduction in greenhouse gas emissions of more than 30% lowered the price of modelled consumption, but took a toll on nutritional quality.
This goes to show that compliance with recommendations on macronutrients is not enough to guarantee nutritional quality. It is the ADEQ model that will generate nutritionally adequate consumption while ensuring that greenhouse gas emissions are steadily decreased:
- For nutritional needs to be met, there must be an immediate increase in the quantity of fruits and vegetables consumed.
- To reduce greenhouse gas emissions while maintaining the nutritional value of diets, the quantity of meat, and especially the meat of grazing animals and delicatessen meats, must be gradually diminished.
- Lastly, to reduce greenhouse gas emissions by more than 40%, meat and dishes containing meat must be entirely phased out, and the amount of starchy foods (potato and grains) increased. It is even feasible, in theory, to reach a 60% reduction in greenhouse gas emissions with the ADEQ model. But social acceptability, which is a cornerstone of sustainable diets, risks being seriously undermined, as the consumption proposed here is a far cry from established norms.
This study therefore reveals that nutritional quality must be taken into careful consideration and recognised as a key indicator when it comes to boosting the sustainability of diets. Since sustainable diets must also be realistic diets, a 30% cut in greenhouse gases seems a reasonable goal, attainable through better food choices. Improving food production and transforming food systems are also avenues that should be explored, to further cut back on the environmental impact of human food consumption.
A hybrid methodology for a standardised evaluation of the carbon footprint of diets
The same INRA team, working hand in hand with AgroParisTech, also recently published in the journal PLOS ONE a study1 designed to compare and assess the strengths and limits of two databases on the greenhouse gas emissions of the most popular foods in France. The first consisted of data on greenhouse gas emissions from scientific literature (Life Cycle Assessments (LCA) published for specific foods), while the second was obtained using a hybrid method (LCA and an Output-Input approach) allowing for a standardised assessment of the environmental impact of generic foods. This study revealed the advantages of the hybrid method, supporting its use for the analysis of sustainable foods in epidemiological studies.
Bertoluci G, Masset G, Gomy C, Mottet J, Darmon N. How to build a standardized country-specific environmental food database for nutritional epidemiology studies. PLOS ONE. April 7, 2016.
1This study was financed by the French National Research Agency’s OCAD project (Offrir et Consommer une Alimentation Durable) on sustainable diets, and by the Daniel and Nina Carasso foundation, within the framework of the AVASUN project (assessing the bio-availability of nutrients in sustainable diets).
2Individual and national study on food consumption, carried out in France in 2006-2007.
Pérignon M, Masset G, Ferrari G, Vieux F, Maillot M, Amiot MJ, Darmon N. How low can dietary greenhouse gas emissions be reduced without impairing nutritional adequacy, affordability and acceptability of diet? A modelling study to guide sustainable food choices. Public Health Nutrition, 8 April 2016