Decreasing absorption of heavy metals: the role of phytates


Consumption of fish from marine environments is the main source of human exposure to mercury. Inorganic mercury is transformed into methylmercury accumulating through the food chain, leading to high concentrations at the top of the aquatic food chain. As such, larger, longer-living fish are frequently higher in methylmercury than smaller, shorter-lived fish at the bottom of the food chain. Many studies have shown the nutritional benefits of eating fish, which is not only a rich source of omega-3 but is also high in protein and other nutrients, including numerous vitamins and minerals. Concerns about chemical and environmental pollutants being found in fish, including mercury, PCBs and dioxins, has led to confusion among the public, raising the question ‘do the risks of eating fish outweigh the benefits?’ (Mahaffey et al, 2011)

The omega-3 polyunsaturated fats EPA and DHA are essential for normal cellular function and are also converted to hormone-like substances called ‘eicosanoids’ and ‘docosanoids’, which are involved in the regulation of immunity, platelet aggregation and inflammation. Marine sources provide our major dietary intake and we are advised that two portions of fish weekly are required to meet government recommendations of EPA and DHA of 0.45g/day. Given the wide-ranging and increasing evidence that deficiencies in omega-3 play a role in numerous health conditions and diseases, it is generally accepted that consuming fish is more beneficial than the risks encountered through contamination of mercury, PCBs and dioxins; importantly, it should be understood that it is possible to choose fish species that are rich in omega-3 but low in contaminants.

Although fish can be eaten raw (e.g. as sushi), a variety cooking methods are generally employed, including steaming, boiling, grilling, baking and frying, all of which influence the bio-availability of compounds such as methylmercury. Although cooking does not significantly modify methylmercury concentrations in fish compared to uncooked fish, it has a profound effect on bio-accessibility, or that which is absorbed during digestion. Interestingly, of the above methods frying or boiling fish have the greatest influence on decreasing the absorption of methylmercury when compared to raw fish, which has the highest absorption rate. Furthermore, it is noteworthy that drinking phytate-containing beverages such as green tea, black tea or coffee simultaneously with eating fish can also decrease fish mercury absorption. Decreasing absorption of heavy metals in fish and are chelating agents that can bind to certain dietary minerals including iron, zinc, manganese and, to a lesser extent, calcium, and slow their rate of absorption. We are advised not to consume tea or coffee with meals for this very reason; however the combined effect of cooking and the addition of tea or coffee can lead to very low levels of methyl mercury absorption when consuming fish (Ouedraogo & Amyot 2011).

Attempting to maximize dietary intake of omega-3 whilst minimising contaminant exposure can be achieved to some extent through careful food choices and through cooking methods utilised. However, boiled fish may not be to everyone’s liking, and frying fish can lead to loss of omega-3 during the cooking process. The simplest way to ensure your omega-3 needs are met is through the use of purified and concentrated fish oil, which offers a safe and convenient alternative to fish consumption itself and may be more suitable for those individuals who are actively seeking to avoid ingestion of heavy metals.

Igennus supplements are routinely independently batch tested and certified free of mercury, PCBs and dioxins.

1. Mahaffey KR, Sunderland EM, Chan HM, Choi AL, Grandjean P, Marien K, et al. Balancing the benefits of n-3 polyunsaturated fatty acids and the risks of methylmercury exposure from fish consumption. Nutr Rev 2011;69(9):493-508.
2. Ouedraogo O, Amyot M. Effects of various cooking methods and food components on bioaccessibility of mercury from fish. Environ Res 2011;111(8):1064-9.

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Dr Nina Bailey

About Dr Nina Bailey

Nina is a leading expert in marine fatty acids and their role in health and disease. Nina holds a master’s degree in Clinical Nutrition and received her doctorate from Cambridge University. Nina’s main area of interest is the role of essential fatty acids in inflammatory disorders. She is a published scientist and regularly features in national health publications and has featured as a nutrition expert on several leading and regional radio stations including SKY.FM, various BBC stations and London’s Biggest Conversation. Nina regularly holds training workshops and webinars both with the public and health practitioners.