Development and validation of an individual sustainable diet index in the NutriNet-Santé study cohort

SDI Index

The Nutrition Society Paper of the Month for June is from the British Journal of Nutrition and is entitled ‘Development and validation of an individual sustainable diet index in the NutriNet-Santé study cohort’ by authors Louise Seconda, Julia Baudry, Philippe Pointereau, Camille Lacour, Brigitte Langevin, Serge Hercberg, Denis Lairon, Benjamin Allès and Emmanuelle Kesse-Guyot.

Changes in dietary patterns observed in recent years have played an important role in over-reaching planetary boundaries and increasing global inequalities. Thus, in order to ensure a healthy diet for a growing population while also balancing planetary resources and maintaining social and cultural aspects related to food, the FAO define sustainable diets as those “protective and respectful of biodiversity and ecosystems, culturally acceptable, accessible, economically fair, and affordable; nutritionally adequate, safe, and healthy; while optimizing natural and human resources”.

Recently, extensive studies have focused on the identification of more sustainable dietary patterns. Many indicators have been proposed to assess the sustainability of diets at the individual level. However, despite the growing interest in this topic, the identification of more sustainable diets remains challenging because of the use of few indicators concomitantly, most of which are related to the environmental or nutritional dimensions of sustainability, while a notable under-representation of social or economic indicators has been highlighted. Moreover, authors report potential tensions between some indicators.

The purpose of this study was thus to develop a validated index, the sustainable diet index (SDI), to assess and compare the sustainability of dietary patterns in the NutriNet-Santé French cohort taking into account multiple indicators based on current scientific knowledge and covering the four dimensions of diet sustainability: environmental, nutritional, economic and sociocultural. The SDI’s content validity was tested to estimate the content representativeness or relevance of the index indicators. The construct validity of the index was also assessed by using external sustainable guidelines.

In our sample, the SDI was highly correlated to all dimensions, and all sub-indexes substantially contributed to the participants’ ranking. The environmental and economical sub-indexes were the most and least correlated with the SDI respectively. Dietary patterns of those participants with a high SDI (considered as more sustainable) were concordant with already published sustainable diet guidelines. That is to say, we observed a smaller contribution of animal food (meat and processed meat, dairy products and milk, seafood and fish), alcoholic beverages, fruit juices, soups, sweet foods and high contribution of fruits, vegetables and legumes in diets when the SDI increases.

In conclusion, the SDI could be a useful tool to easily assess the sustainability of diets, to follow sustainability-related changes in dietary patterns, to study the associations with long-term health outcomes and to help in guiding future public health policies.