PhD Defence by Anna E. Jacob

Principal supervisor:

• Senior Researcher Lea Sletting Jakobsen

Co-supervisors:

• Senior Researcher Sara M. Pires
• Associate Professor Marianne Uhre Jakobsen
• Professor Olivier Jolliet

Examiners:

• Senior Researcher Ellen Trolle, DTU Food
• Professor Lukas Schwingshackl, Universitätsklinikum Freiburg
• Docent Elinor Hallström, Research Institute of Sweden

Moderator at defence:

• Senior Researcher Morten Poulsen

Resume
Current diets have negative effects on our environmental footprint and chronic disease burden. This has sparked a growing interest in more plant-forward diets (such as vegan, vegetarian, flexitarian, etc.) as an avenue to achieve sustainability targets. According to the WHO and FAO, weighing the benefits and potential risks of these diets is a key step to their adoption and transformation of the food system.

This thesis explored the health and environmental impacts of sustainable diets through five scientific papers. First, the existing research was reviewed to scope how different dietary patterns were defined and what evidence existed in terms of health outcomes (Paper I). In the data-focused investigations, a food-specific database of greenhouse gas emissions was updated (Paper II), and a harmonised database of dietary risk factors was established (Paper III). Findings from these background and foundational efforts supported the final two modelling studies, which examined how shifting to more plant-forward diets might affect population health in Aotearoa New Zealand (NZ) and Denmark (DK), respectively.

Using similar dietary scenarios, two separate modelling approaches were applied. In NZ, a multi-state life table model (Paper IV) demonstrated increasing health, environmental, and healthcare cost benefits with increasingly plant-forward eating. However, a risk-benefit assessment applied (Paper V) to the Danish population, which incorporated food safety aspects, providing conflicting results. This model suggested that more plant-forward diets could lead to negative health outcomes, although there was considerable uncertainty in these estimates.

Together, these findings show that the choice of risk data and modelling method play a major role in conclusions from dietary assessments. Newly emerging evidence, such as links between dairy or fish intake and lower dementia risk, can shift result directions and highlight important trade-offs. Simple advice to eat more plant-forward, without considering food substitutions and changes in behaviour, may not be sufficient for improved public health. Insights from this thesis can support decision makers in the development of food-based dietary guidelines and policy interventions.

A copy of the PhD thesis is available for reading at the department.