Healthy and sustainable diets in the 21st century from an individual and societal perspective

The first part of this thesis focused on the individual perspective of healthy and sustainable diets. Here, we investigated the association between adherence to various healthy and/or sustainable dietary patterns in relation to cardiovascular disease, all-cause mortality and environmental impact indicators. We observed that adherence to the Dutch dietary guidelines (Chapter 2) and adherence to the DASH diet (Chapter 3) were significantly associated with lower risk of heart failure in the EPIC-NL cohort. Additionally, we observed that adherence to the EAT-Lancet Healthy Reference Diet, a set of dietary recommendations which have been proposed to co-benefit human and planetary health, was associated with lower risk of coronary heart disease and all-cause mortality in EPIC-NL (Chapter 4). With regard to sustainability, high adherence to the Healthy Reference Diet was associated with 1.7% lower impact from greenhouse gas emissions, 3.2% less land use, 0.5% less freshwater eutrophication, 3.5% less marine eutrophication, 6.3% less terrestrial acidification, but with 31.4% more blue water use (Chapter 4). Similarly, we observed that high adherence to the Healthy Reference Diet was associated with a lower risk of coronary heart disease and stroke the pan-European EPIC cohort (Chapter 5).
The second part of this thesis focused on the societal perspective of healthy and sustainable diets, zooming in on the role of the food environment. In Chapter 6, we systematically reviewed evidence on the effectiveness of nudges in promoting healthy dietary choices within real-life food purchasing environments. Additionally, we explored evidence for a moderating role of SEP. Information and position nudges showed modest tendencies towards beneficial effects, although findings were not meta-analyzed due to the substantial heterogeneity in underlying evidence encountered. The scarcity of evidence and the use of different proxies of SEP made it difficult to draw firm conclusions on the potentially moderating role of SEP. In Chapter 7, we studied the association between relative exposure to fast-food restaurants and diet quality, overweight, and obesity in the EPIC-NL cohort, revealing null associations. In Chapter 8, we aimed to explore how the determinants of food choice shape the perceptions regarding supermarket-based nudging strategies among adults with low SEP. In a qualitative study including 15 interviewees with lower SEP, we observed that interviewees evaluated supermarket-based nudging strategies more positively when they aligned with their product preferences, information needs and beliefs about the food environment. At the same time, we observed that some interviewees distrusted supermarket engagement in health-promoting initiatives, suspecting ulterior motives.
From this thesis, it is concluded that on an individual level, consuming dietary patterns rich in plant-based foods and including moderate amounts of animal-sourced foods may benefit both cardiovascular and planetary health. The food environment is an important determinant of food choice, but it remains difficult to quantify its effects. The complex systems perspective acknowledges that causes for poor diets are multifactorial and dynamic, stressing the need for policy action on multiple levels. As such, the food environment can be leveraged as entry-point for promoting healthy and sustainable food choices at a societal level.