The impact of dietary changes targeting environmental metrics on micronutrients status: a systematic literature review

Sustainable dietary practices are at the forefront of current discussions in nutrition, with much attention being drawn to environmental metrics such as greenhouse gas emission (GHGE). However, the definition of sustainable diets is multifaceted and encompasses cultural acceptability, affordability, and importantly, health and nutrient adequacy. Given the global high prevalence of micronutrient deficiencies across diverse economic contexts, there is mounting concern about the risk of nutrient inadequacies when dietary recommendations exclusively prioritize environmental factors. This approach can lead to the substitution of animal-source foods, which are often high in bioavailable micronutrients, with plant-based foods, which often have different nutrient profiles or reduced bioavailability.

To this effect, a 2024 systematic review of 56 studies (1 randomized control trial and 55 observational studies published between 2011-2022) examined how dietary modifications that target environmental metrics impacted the intake of the following 8 micronutrients: zinc, calcium, iron, iodine, folate, and vitamins A, D, and B₁₂.

Overall, the review’s findings indicate generally lower intakes of zinc, calcium, and vitamins B₁₂, A and D following the replacement of animal protein with plant-based proteins. In fact, according to the randomized control trial, when 70% of protein intake came from plants sources, the risk of inadequate intakes of zinc, iodine, and vitamin B₁₂ increased. Moreover, despite an observed increase in total iron and folate intake, authors noted that this iron had low bioavailability. 

Importantly, the authors underscore the high prevalence of baseline micronutrient inadequacies, further emphasizing the importance of considering nutrition when making sustainable dietary recommendations, in order to address nutrient inadequacies rather than exacerbate them. Lastly, it is critical to consider the different micronutrient needs throughout the life cycle and the importance of adapted dietary guidance, as certain vulnerable groups are at higher risk of deficiencies. For example, this review found an increased prevalence of inadequate calcium intake among children and adolescents with reduced dairy intake, as well as the inability of the Planetary Health Diet by the EAT Lancet in meeting both calcium and vitamin D needs in children. 

In light of their findings, the authors discuss the importance of considering bioavailability when assessing micronutrient intake due to the fact that certain nutrients in plant-based foods have reduced absorption, which only a few studies considered. They also note the benefits of distinguishing plant-protein sources, as there is great variability in micronutrient and protein content and for many imitation products, inconsistent fortification practices. 

The authors mention important challenges with data synthesis, in part due to variability in methodology between studies and inconsistent reporting of micronutrient intake outcomes, thus highlighting the need for further robust studies.