Impact of consuming an environmentally protective diet on micronutrients: a systematic literature review

BACKGROUND: A global move toward consumption of diets from sustainable sources is required to protect planetary health. As this dietary transition will result in greater reliance on plant-based protein sources, the impact on micronutrient (MN) intakes and status is unknown. OBJECTIVE: Evaluate the evidence of effects on intakes and status of selected MNs resulting from changes in dietary intakes to reduce environmental impact. Selected MNs of public health concern were vitamins A, D, and B12, folate, calcium, iron, iodine, and zinc. METHODS: We systematically searched 7 databases from January 2011 to October 2022 and followed the PRISMA guidelines. Eligible studies had to report individual MN intake and/or status data collected in free-living individuals from the year 2000 onward and environmental outcomes. RESULTS: From the 10,965 studies identified, 56 studies were included, mostly from high-income countries (n = 49). Iron (all 56) and iodine (n = 20) were the most and least reported MNs, respectively. There was one randomized controlled trial (RCT) that also provided the only biomarker data, 10 dietary intake studies, and 45 dietary modeling studies, including 29 diet optimization studies. Most studies sought to reduce greenhouse gas emissions or intake of animal-sourced foods. Most results suggested that intakes of zinc, calcium, iodine, and vitamins B12, A, and D would decrease, and total iron and folate would increase in a dietary transition to reduce environmental impacts. Risk of inadequate intakes of zinc, calcium, vitamins A, B12 and D were more likely to increase in the 10 studies that reported nutrient adequacy. Diet optimization (n = 29) demonstrated that meeting nutritional and environmental targets is technically feasible, although acceptability is not guaranteed. CONCLUSIONS: Lower intakes and status of MNs of public health concern are a potential outcome of dietary changes to reduce environmental impacts. Adequate consideration of context and nutritional requirements is required to develop evidence-based recommendations. This study was registered prospectively with PROSPERO (CRD42021239713).