The Brazil nut is the largest known plant supplier of selenium. The range of the Brazil nut tree is in the tropical rain forests of South America.
It is interesting to note that the capsular fruits do not come from plantations, but exclusively from wild crop collections. During the rain period, they are collected on the ground and brought to collection sites. There are only three countries in the world that produce significant quantities of Brazil nuts: Brazil, Bolivia, and Peru.
Brazil nuts have a high protein and fat content – up to 70 %. Compared to other types of nuts, the Brazil nut also has a very high share of mineral substances and trace elements (calcium, magnesium, copper, phosphor, selenium, and zinc). [1]
The selenium content in Brazil nuts is so high that the consumption of larger quantities poses the risk of an overdosage. Depending on where the Brazil nut tree has grown, a single Brazil nut can contain up to 400 micrograms of selenium. [1] For comparison: The German Nutrition Society (DGE) recommends only 70 micrograms selenium daily.
Besides selenium, the Brazil nut tree also enriches natural radioactivity in the form of radium. Brazil nuts can have a radium content that is 1,000 times higher than the total nutrition in Germany.
As a result, even the consumption of two Brazil nuts per day can increase the radiation load of food by about half. This alone does not indicate, however, that anyone has to expect negative consequences to their health. Nevertheless, the German Federal Office for Radiation Protection (BfS) advises against assuming the risk of an additional radiation load and, instead, recommends the intake of dietary supplements to cover the selenium requirement. [2]
Besides, Brazil nuts are particularly susceptible to aflatoxines. [1] Even in minor quantities, these mycotoxines can be carcinogenic and mutagenic. Again and again, official controls have detected aflatoxine values in Brazil nuts during official controls that go far beyond the limit values specified by the EU. For this reason, there are import restrictions in the EU for Brazil nuts. [1]
On the Internet, one can see this recommendation everywhere: “Eat two Brazil nuts a day to cover your selenium requirement.” But caution is advised here. Studies have shown: Even just one Brazil nut a day can raise the selenium level far beyond the recommended reference range within two months. [3, 4]
References:
[1] Cardoso BR et al. Food Res Int. 2017 Oct; 100(Pt 2): 9-18. Brazil nuts: Nutritional composition, health benefits and safety aspects.
[2] Bundesamt für Strahlenschutz, Stand November 2022
[3] Donadio JLS et al. Clin Nutr. 2018 Mar 23. pii: S0261-5614(18)30123-7. Genetic variants in selenoprotein genes modulate biomarkers of selenium status in response to Brazil nut supplementation (the SU.BRA.NUT study).
[4] Rita Cardoso B et al. Eur J Nutr. 2016 Feb; 55(1): 107-16. Effects of Brazil nut consumption on selenium status and cognitive performance in older adults with mild cognitive impairment: a randomized controlled pilot trial.
