Do individual sustainable food purchase motives translate into an individual shift towards a more sustainable diet? A longitudinal analysis in the NutriNet-Santé cohort

Many studies have demonstrated the environmental and health weaknesses of the food systems and the need for transformation is now recognised. Although some consumer segments seem to be more aware of sustainability issues, sustainable motives do not systematically translate into purchasing behaviour. The aims of this study were to identify a typology of dietary changes and to analyse whether these actual dietary changes towards more sustainable consumption during the years 2014–2018, (considering nutritional quality, plant-based foods and organic consumption) were related to a set of consumer food purchase motives measured in 2013. In the French NutriNet-Santé cohort, 13,292 individuals completed a food frequency questionnaire in 2014 and 2018 and a validated food purchase motives questionnaire in 2013, with a particular focus on sustainability. A typology was built to identify clusters using a Reduce Rank Regression (RRR) statistical model, with differences in food consumption as predictor variables and a set of dietary scores (reflecting nutritional quality, plant-based food and organic consumption) as response variables. Associations between dietary changes and food purchase motives were evaluated using ANCOVA. Participants with the most sustainable diet in 2014 and that has continued to improve over time (increased healthy plant-based foods and organic consumption) showed higher sustainable food-purchase motives. These were more often women, young and graduates. Participants with the lowest sustainable motives had at the same time a rather unsustainable diet and changed to a greatly improved diet in 2018. Participants with strong motives related to price, innovation and convenience showed a decrease in diet quality over time (increase in unhealthy plant- and animal-based food, alcoholic drinks, decrease in organic consumption). This cluster had the highest proportion of men, less educated and older than 65. Our results indicate that a part of the population was interested in sustainable food purchase and improved the sustainability of their diet over a short period of time. Some participants, with specific socio-demographic characteristics, were unaware of their diet's sustainability. Therefore, targeting awareness of food sustainability to a certain part of the population is essential.