Impact of a transition to diets from sustainable sources on micronutrient intakes and status
Background: A global transition to diets from sustainable sources is required for planetary health. This transition will result in greater reliance on plant-based protein sources coupled with reductions in animal source foods. The evidence base underpinning the formulation of nutrition policy lacks data on the feasibility, safety and effectiveness of translating sustainable dietary guidelines into practice in the population, which could pose risks to nutrition for large sectors, including females of reproductive age and children. Objective: The aim of this thesis was to explore of the impact of a transition to diets from sustainable sources on micronutrient (MN) intakes and status. Objectives were to systematically review the existing evidence assessing the impact of following environmentally protective diets on MN intakes and status (Chapter 2); design and conduct a first-of-its-kind dietary intervention trial of an environmentally protective diet (Chapter 3); assess the impact of the intervention on MN intakes (Chapter 4) and status (Chapter 5); and explore the potential for dietary modelling to assist the development of MN adequate diets from sustainable sources (Chapter 6). Methods: PRISMA guidelines were followed to conduct a systematic literature review (SLR) of studies reporting MN and environmental outcomes, searching seven databases from January 2011 to October 2022 (Chapter 2). Chapters 3 to 5 describe a 12-week, three-centre, single-blind, parallel, randomised controlled trial (RCT) among 355 healthy participants aged 18-64 years, known as MyPlanetDiet. The intervention provided participants with personalised dietary advice based on their dietary habits, in line with sustainable healthy principles (intervention arm) or dietary guidance based on the Irish and Northern Irish healthy eating guidelines (control arm). Outcomes included changes in dietary environmental impacts, energy, protein, MN intakes, the prevalence of inadequate intakes and changes in MN status throughout the intervention. Chapter 6 describes a narrative review of diet optimisation studies that design diets considering nutritional, environmental and context-specific constraints. Results: The SLR (Leonard et al., 2024) included 56 studies; one RCT which provided the only biomarker data; 10 dietary intake studies, and 45 dietary modelling studies, including 29 diet optimisation studies. Most studies suggested that intakes of zinc, calcium, iodine, and vitamins A, B12 and D would decrease, and total iron and folate would increase in a dietary transition to reduce environmental impacts, with similar findings for the prevalence of inadequate intakes, reported in only 10 studies. In the MyPlanetDiet RCT, dietary GHGE decreased from baseline to endpoint in both arms and was lower in the intervention arm at endpoint. There were changes in MN intakes in both arms over the 12-weeks, and at endpoint, the intervention arm had lower intakes of energy, protein, thiamin, riboflavin, niacin, vitamins D, B6, B12 and C, calcium, zinc, potassium, selenium and iodine, and higher intakes of vitamins A, E and K1 (P < 0.05) compared with controls. The prevalence of inadequate intakes of riboflavin, calcium, zinc, vitamins B6, B12 and C was higher, and of vitamin E and copper was lower (P < 0.05) among females in the intervention arm than controls. Among males, the prevalence of inadequate intakes of riboflavin, selenium and iodine was higher in the intervention arm than controls (P < 0.05). Changes in biomarkers of nutritional status analysed for this thesis were minimal over the 12 weeks. Our narrative review of diet optimisation studies (Leonard & Kiely, 2024) identified a range of diets that meet individual MN requirements, have reduced environmental impacts, and minimise deviation from culturally acceptable dietary practices. Although these are theoretical solutions, opportunities arising from the results of diet optimisation studies include supporting the development of food-based dietary guidelines and exploring food-based strategies to increase nutrient supply, such as fortification. Conclusions: The findings from our SLR, mainly based on observational data, and the MyPlanetDiet RCT aligned, identifying several key MNs that are at risk in the transition to diets from sustainable sources, particularly among females. Greater emphasis on meeting diverse MN requirements from appropriate dietary sources is required in the global discussion around developing diets from sustainable sources. Dietary modelling techniques, such as diet optimisation, can be a useful tool in the generation of hypotheses and diet solutions for testing in further intervention studies among diverse populations.
Micronutrients, Sustainable healthy diets
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