Iodine concentration of fortified and unfortified plant-based alternatives to milk, dairy products, eggs and fish

Animal foods, especially dairy products, eggs and fish, are the main source of iodine in the UK. However, the use of plant-based alternative products (PBAP) is increasing owing to issues of environmental sustainability. We previously measured the iodine content of milk-alternatives (1) but data are lacking on the iodine content of other plant-based products and there is now a greater number of iodine-fortified products. We aimed to compare: (i) the iodine concentration of fortified and unfortified PBAP and (ii) the iodine concentration of PBAP with their animal-product equivalents, including those not previously measured such as egg and fish alternatives. The iodine concentration of 50 PBAP was analysed in March 2022 at LGC using ICP-MS. The products were selected from a market survey of six UK supermarkets in December 2021. Samples of matrix-matched (e.g. soya/oat) fortified and unfortified alternatives to milk (n = 13 and n = 11), yoghurt (n = 2 and n = 7) and cream (n = 1 and n = 5) were selected for analysis, as well as egg- (n = 1) and fish-alternatives (n = 10). We compared the iodine concentration between PBAPs and data on their animal-product equivalents (2) . The iodine concentration of fortified PBAPs was significantly higher than that of unfortified products; the median iodine concentration of fortified vs. unfortified milk alternatives was 321 vs. 0.84 µg/kg (p<0.001) and of fortified and unfortified yoghurt alternatives was 212 µg/kg vs 3.03 µg/kg (p = 0.04). The fortified cream alternative had a higher iodine concentration than the unfortified alternatives (259 vs. 26.5 µg/kg). The measured iodine concentration of the fortified products differed from that of the product label (both lower and higher); overall, the measured iodine concentration was significantly higher than that stated on the label (mean difference 49.1 µg/kg; p = 0.018). Compared to the animal-product equivalents, the iodine concentration of unfortified PBAPs was significantly lower for milk (p<0.001) and yoghurt (p<0.001), while there was no difference with fortified versions of milk (p = 0.28) and yoghurt (p = 0.09). The egg alternative had an iodine concentration that was just 0.6% of that of chicken eggs (3.38 vs. 560 µg/kg). Three (30%) of the fish alternatives had kelp/seaweed as ingredients and the median iodine concentration of these products was (non-significantly) higher than those without (126 vs 75 μg/kg; p = 0.83). However, the iodine content of all fish-alternative products was ten-times lower than that of fish (median 99 vs. 995 µg/kg; p<0.001). The majority of PBAP are not fortified with iodine but those that are fortified have a significantly higher iodine concentration than unfortified products and are closer to the value of their animal equivalents. From an iodine perspective, unfortified plant-based alternatives are not suitable replacements and consumers should ensure adequate iodine from other dietary sources. Manufacturers should consider iodine fortification of a greater number of plant-based alternatives.