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There is a deficit of mineral micronutrients in global food systems, known as ‘hidden hunger’, especially in the global south. This review focuses on zinc (Zn) and iron (Fe), whose entry into food systems depends primarily on soil and crop factors. Approaches to increase dietary supplies of Zn and Fe include: (1) supplementation, (2) food fortification, (3) dietary diversification, and (4) crop biofortification, including breeding and fertilizer-based approaches. Supply-based estimates indicate that Zn deficiency might be more widespread than Fe deficiency in sub-Saharan Africa, although there are major knowledge gaps at an individual biomarker level. Recent analytical advances, including the use of stable isotopes of Zn and Fe, can play an increasing role in improving our understanding of the movement of micronutrients in food systems, and thereby help to reduce the immense human cost of ‘hidden hunger’. [ABSTRACT FROM AUTHOR]

• Total Se in crops was increased by c. 10x after addition of fertiliser enriched with Se. • Soil and fertiliser-derived Se were transformed into similar species in edible portions of crops. • More than 90% of extracted species were in an organic form, dominated by selenomethionine. • Legumes (cowpea and groundnut) accumulated more Se than cereals (maize). The purpose of this research was to explore the speciation and bioaccessibility of native soil-derived selenium (Se) versus Se applied via fertiliser in the edible portions of maize, groundnut and cowpea grown in Malawi. Fertiliser-derived Se, applied as isotopically labelled selenate, contributed 88–97% of the total Se in the edible portions. Both soil and fertiliser-derived Se were transformed into similar species, with more than 90% of the extracted Se in an organic form. The main form of fertiliser-derived Se in grain was selenomethionine with an abundance of 92.0 ± 7.6% in maize, 63.7 ± 6.2% in cowpea and 85.2 ± 1.9% in groundnut. In addition, cowpea contained 32.7 ± 6.2% of Se-methyl-selenocysteine. The mean bioaccessibility of fertiliser-derived Se was 73.9 ± 8.5% with no statistically-significant difference across all crops despite some variation in speciation. Understanding the contribution of fertiliser-derived Se to the formation of organic forms of Se in crops is crucial, given that organic Se species are more bioaccessible than inorganic forms. [ABSTRACT FROM AUTHOR]